Why do people develop allergies?

More Adults are Waking Up with Brand New Allergy Symptoms

For the lucky majority of Americans who’ve never suffered from allergies, spring and summer are usually uncomplicated stretches of natural bliss. Unencumbered by watery eyes and runny noses, they get to frolic amongst blooming vegetation or tussle with the denizens of local dog parks with abandon. But every now and then, one of these smug adults will step outside, take a deep breath, and feel a wholly unexpected nasal irritation or a welling of tears for the first time in his or her life.

As these unlucky few soon learn, adults can develop allergic symptoms at any time, even fairly late in life. No one knows for sure how many of us will fall victim to this unexpected pain in the ass, but the risk theoretically hovers over everyone, no matter how remote it may be. And some reports suggest the number of adults suddenly manifesting environmentally triggered sniffles could be on the rise. The reality that one could live life carefree one day and wake up the next in bleary fatigue is hard to contend with, especially when so few of us understand how or why these sudden latter-day allergic responses could be triggered.

An estimated 30 to 40 percent of Americans will likely suffer from allergies at some point, most of them triggered by airborne irritants like pollen outside or pet dander or dust mites inside and only a comparative few of them triggered by foods. According to Stephen Tilles, president of the American College of Allergy, Asthma, and Immunology, these folks are born with a genetic predisposition for allergies, but then triggered when they’re exposed to a specific allergen—although sometimes that trigger is dependent on additional, little-understood epigenetic triggers. These allergens, although factually harmless, lead prone immune systems to overreact, producing a glut of histamines that can cause irritation in localized areas, or in extreme causes lead to full-body reactions and life-threatening airway closures. Even mild allergies can still lead to real misery and temporary impairment.

The vast majority of people develop allergies as children, when first exposed to triggering allergens. Some people’s allergic responses might fluctuate through their teenage years as their bodies—namely their hormones—change rapidly. But Tilles says most people will have developed a stable allergic profile in their 20s. If they “haven’t developed allergies by the time they’re 30,” he adds, “it’s very unlikely they’re going to later on.” In fact some research actually suggests that as people age their allergies tend to decrease or vanish, although that is unfortunately due to the weakening of the immune system over time.

Beyond this point, Tilles says, most people will only develop allergies if they make a major life change, like a move to a new region, that finally exposes them to a substance they’ve always been predisposed to have an allergic reaction to. It’s also possible that people who haven’t moved or encountered a new environment are just manifesting allergies they had when younger, but then went dormant for an oddly longer period of time (perhaps beyond the usual teenage years of hormonal flux) and were only reactivated by some mysterious trigger.

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It’s also possible, some doctors speculate, for someone with perhaps a minor allergic inclination to undergo some health event that causes an upheaval in their immune system later in life that might suddenly make it newly sensitive to an allergen. This could be anything from pregnancy to an infection to a major and sickening stretch of stress. (These events may help explain why some people’s latent and forgotten or previously minor childhood allergies surge back, too.)

“We are still humble about this,” Tilles says. “We’ll still skin test for allergies in elderly patients who come in with new onset symptoms. But it’s relatively rare for them to have proven allergic causes if they’ve never had any. It certainly can happen, but it’s not common.”

It’s far more common, Tilles says, for adults to develop non-allergic nasal allergy symptoms out of nowhere. Although indistinguishable symptomatically from allergies for patients, this issue, which Tilles says accounts for about a third of any allergist’s patients, is triggered not by distinct allergens and the antibodies they conjure up but by general irritation. “There are sub-groups that are, for example, only triggered by barometric pressure changes,” he explains, “and others that are only triggered by irritants or something like that. There are others that look like allergic inflammation, but we just can’t determine that there’s an allergen .”

We do know, Tilles says, that smokers or workers in industrial jobs involving airborne irritants they aren’t protected from are at increased risk of “non-allergic rhinitis,” as allergists refer to this broad nasal irritation. It’s also possible the same factors that re-trigger or newly awaken adult-onset allergies, or play a role in the emergence or development of childhood onset allergies, could trigger lifelong general sensitivity in people who aren’t genetically disposed to outright allergies.

Beyond that, it’s honestly a bit of a crapshoot who suffers when and who doesn’t. Long story short, adult onset allergies aren’t really a discrete thing. They’re the murky common symptom of a ton of different possible exposures or exacerbations, many of which even the nation’s foremost allergists only have a basic grasp on. For those wishing to avoid the unique pain of developing allergic symptoms late in life, that is not useful information. Unless one wants to build a bubble of environmental consistency and can somehow avoid major immune system shifts, the risk of waking up snuffling, fatigued, and miserable will always lurk in life.

But on the limited bright side, Tilles says, allergic symptoms are rarely dangerous. They do suck—massively. Still, there are a number of solid treatments available, many of them over the counter. Most treatments meant for allergies will be effective for non-allergic rhinitis as well. And most irritants can be avoided with a bit of planning. Managing irritant exposure risks and symptoms is far from ideal. We just have to deal with the realities of chaotic bodies as best we can.

Read This Next: The Living Hell of a Latex Allergy

Peanut allergies typically develop during childhood, and children less commonly outgrow them than they do other food allergies. Peanut allergy appears to be equally prevalent among American adults and children.

It has been well established that kids develop allergies to the “top eight” foods: milk, egg, wheat, soy, peanut, tree nuts, fish and shellfish. Most of the reactions in adults occur to the top eight foods as well, according to Dr. Sharon Chinthrajah, an assistant professor at the Stanford University School of Medicine and medical director of the Sean N. Parker Center for Allergy and Asthma Research, which was involved in shaping the survey. That said, shellfish allergy is more common among adults than among children, as it tends to appear later in life.

Several patterns have been observed that are unique to adults who develop new food allergies. One is called oral allergy syndrome, which occurs in a small percentage of adults who have seasonal allergies. It “involves your body getting tricked,” said Dr. Chinthrajah. She explained that some adults might have allergies to tree pollen, for example, and some of the tree proteins are similar to those in fruits and vegetables, “so when your body eats the raw form of those foods, it thinks you’re eating tree pollen.” Birch tree pollen, for instance, bears similarities to proteins found in fruits like peaches, apples and cherries. The main symptom is typically an itchy mouth or throat. Interestingly, if the fruit is first processed or cooked in any way, it denatures the protein and does not produce the same reaction.

Many adults who develop a new food allergy wonder what caused it — the “turn-on switch” as Dr. Gupta calls it. Anecdotal reports suggest that pregnancy, for example, can trigger new allergies, leading some to hypothesize that a hormonal connection may be at play. Other patients report they noticed a new allergy after getting a viral infection. Still, it is not yet clear what causes a new reaction to a food after someone has eaten it for decades without incident.

Importantly, an allergic reaction is not the same as a food intolerance. An allergic reaction is characterized by marked symptoms, such as itching, hives, swelling, trouble breathing or vomiting, within two hours of consuming the food in question. Symptoms that appear the next day may be characteristic of a food intolerance, which Dr. Chinthrajah said researchers do not yet understand as well as they understand food allergies.

May/June 2015

Late-Onset Food Allergies
By Larissa T. Brophy, MS, RDN, LD
Today’s Geriatric Medicine
Vol. 8 No. 3 P. 8

As individuals age, so do their immune systems. With the significant increase in life expectancy, it’s projected that by 2050, more than 80 million adults will be aged 65 or older while another 20 million adults will be aged 85 or older. This rapidly growing geriatric population will experience immunosenescence, the aging of the immune system.

Immunosenescence affects the innate and adaptive immune system, causing specific changes in the various cell types of the immune system. For mast cells, a key cell type involved in the food allergy reaction, aging reduces degranulation and causes dysregulation in function. The latter change can result in new food allergy development, whereas the former may diminish physical symptoms of a food allergy and delay medical attention. Food allergy is an increasing health concern in the geriatric population.

In the elderly, the prevalence of food allergies is estimated at 5% to 10%,1,2 but is likely underestimated and underdiagnosed, and thus undertreated. A study reported that 24.8% of geriatric nursing home patients (mean age of 77) were positive (skin test) for food allergens.3,4 It is speculated that 25% to 30% of adults self-diagnose food allergies, but the true prevalence is approximately 5% in industrialized countries.4,5 Notably, food allergies can develop at any time and are not limited to manifestation in the pediatric population.

In the elderly, confounding factors include decreased stomach acid (leading to decreased protein digestion and increased in vivo exposure to absorbed allergenic epitopes) and an age-related decrease in total serum immunoglobulin E (IgE).

Conversely, alcohol consumption greater than 14 units per week significantly increases total serum IgE concentrations, which correlates with positive food allergen tests. These various factors may induce de novo sensitization to food allergens, increasing the need for continuous screening and diagnosis. In the geriatric population, typical diagnostics may be insufficient to detect a food allergen but should continue to be the starting point as shown in Table 1. Self-diagnosis needs to be eliminated because the subsequent self-management may lead to nutritional inadequacy, potential nutrient deficiencies, and increased frailty from over-restricting food intake.

Malnutrition, another significant concern in the elderly, plays a critical role in immune system maintenance and efficiency. The three micronutrients of concern are vitamin D, zinc, and iron. An insufficiency or deficiency in calcitriol, the active form of vitamin D, may negatively affect food-related IgE reactions (nonlinear association). Poor zinc bioavailability (absorbed from food) and in vivo homeostasis may further alter the immune efficiency, favoring the development of food allergies. Iron deficiency has also been associated with immune system issues, decreasing antibody responses and increasing the risk of food allergy. In these cases, correcting any deficiencies through vitamin and/or mineral supplementation should improve outcomes and possibly reduce the incidence of any deficiency-related allergies. Blood measurements for zinc, iron, and vitamin D are easily obtainable. (Note: zinc measurements may not indicate a deficiency and should be coupled with risk factors and symptoms.)

Symptoms of food allergies can range from mild to severe. A person experiencing anaphylaxis will seek immediate medical attention that results in an easier diagnosis. However, the elderly are less likely to experience anaphylaxis, making detection more difficult. The elderly report mild symptoms that are often nonspecific and can be related to numerous causes. The most common food threats are shown in Table 2.

Health care professionals may not identify the reported symptoms as potential food allergies. Symptoms can involve the skin, nasal passages, eyes, mouth/lips, ears, gastrointestinal tract, or respiratory and cardiovascular systems. The specific symptoms can be incorrectly mistaken for problems with medication(s), sleep deprivation, environmental allergies, gastrointestinal issues, viruses, autoimmune disorders, or attributed to general aging effects. Undiagnosed food allergies (and celiac disease) can contribute to malaise, malabsorption, and inflammation, further exacerbating the risk of frailty. The keys are an accurate diagnosis and appropriate management in the elderly.

Taking Action
Once a food allergy has been diagnosed, the only approved method for effective management is avoiding the allergen. It is important to note that once a food allergen is totally eliminated from the diet, reactions can become more obvious and will usually increase in severity. As to avoidance, some foods are easier to eliminate than others. Food labels containing ingredient lists are essential tools for prepackaged foods. However, when older adults dine out or visit well-intentioned friends and family, avoidance becomes a bit more challenging.

Lack of knowledge and cross-contamination of foods can lead to a reaction. Caution is necessary and may require an individual to ask various questions. Requesting to see an ingredient list from a package or in a recipe may be crucial. If the establishment or the individual is unable to answer questions or produce the requested food label, then it is best to avoid the unknown unless the individual is prepared to deal with a reaction.

For anaphylaxis, injectable epinephrine is required, followed by immediate medical treatment after exposure. For more mild symptoms, antihistamines can be effective in reducing symptoms, but only time will heal. Food allergy management requires vigilance and due diligence to remain safe at all times. Proper food tip recommendations to ensure patients’ safety include the following:

• Read all food labels and recheck periodically, as ingredients will change. It’s important to avoid if uncertain.

• Modify recipes. Many websites provide appropriate substitutions and/or modified recipes.

• Ask questions. Knowledge is essential for management.

• Avoid cross-contamination by cleaning food preparation areas, utensils, dishes, pans, and kitchen appliances. Consider safe equipment when needed (eg, toaster).

• Check out a restaurant’s menu before arrival. If several menu items contain the food allergen, cross-contamination is highly probable.

• Bring safe food to a function, outing, cookout, or holiday dinner. If shared, discard any leftovers, as cross-contamination is likely. Eat a snack or meal prior to attending.

Additional Considerations
Other factors to consider include correcting any nutritional deficiencies, especially iron, zinc, and vitamin D. Supplementation of a daily multivitamin (providing antioxidant vitamins, including A, C, and E; B-complex vitamins; and trace minerals), coenzyme Q10, probiotics, omega-3 fish oil, and L-glutamine may also be beneficial. Use caution with the elderly and prevent overdosing (nutrients more than 100% of the Daily Value) unless deficient.

Some herbs are recommended for immune-enhancing and anti-inflammatory effects, such as green tea, milk thistle, bromelain, turmeric, and cat’s claw, but patients should use extreme caution because of the potential for interactions.

Patients should consume diets rich in omega-3 fats, such as fatty fish including salmon, tuna, mackerel, sardines, and herring, and plant-based sources such as flax, chia seeds, walnuts, canola oil, and fortified foods. In addition to drinking six to eight glasses of filtered water daily and increasing daily probiotic intake by consuming yogurt or kefir, patients should choose fiber-rich foods. Plant-based foods also are sources of phytochemicals, which are compounds that may help.

Other recommendations include avoiding trans fats, which are found in commercial baked goods, processed foods, and stick margarine; aiming for 30 minutes of physical activity, five days per week; and reducing alcohol intake to moderate levels or abstaining altogether. Moderate alcohol intake is defined as one drink per day for women and two drinks per day for men. One drink equals 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proof liquor.

Advise patients to monitor nonfood substances for the food allergen, which can be present in lotions, cosmetics, medications, and hair products. Additionally, patients should use proton pump inhibitors and antacids with caution.

Dietitians who specialize in food allergy management may be able to assist in detection of potential offenders by comparing detailed food logs with self-reported symptoms. A specialized dietitian can ensure nutritional adequacy and balanced menu planning.

— Larissa T. Brophy, MS, RDN, LD, is an assistant professor at Mount Carmel College of Nursing, adjunct faculty at Columbus State Community College, and continues to provide nutritional counseling at Rite for You Nutrition Center. A dietitian for more than 20 years, she suffers from severe adult-onset food allergies.

All About Allergies

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What Are Allergies?

Allergies are abnormal immune system reactions to things that are typically harmless to most people. When a person is allergic to something, the immune system mistakenly believes that this substance is harming the body.

Substances that cause allergic reactions — such as some foods, dust, plant pollen, or medicines — are known as allergens.

Allergies are a major cause of illness in the United States. Up to 50 million Americans, including millions of kids, have some type of allergy. In fact, allergies cause about 2 million missed school days each year.

How Do Allergies Happen?

An allergy happens when the immune system& overreacts to an allergen, treating it as an invader and trying to fight it off. This causes symptoms that can range from annoying to serious or even life-threatening.

In an attempt to protect the body, the immune system makes antibodies called immunoglobulin E (IgE). These antibodies then cause certain cells to release chemicals (including histamine) into the bloodstream to defend against the allergen “invader.”

It’s the release of these chemicals that causes allergic reactions. Reactions can affect the eyes, nose, throat, lungs, skin, and gastrointestinal tract. Future exposure to that same allergen will trigger this allergic response again.

Some allergies are seasonal and happen only at certain times of the year (like when pollen counts are high); others can happen anytime someone comes in contact with an allergen. So, when a person with a food allergy eats that particular food or someone who’s allergic to dust mites is exposed to them, they will have an allergic reaction.

Who Gets Allergies?

The tendency to develop allergies is often hereditary, which means it can be passed down through genes from parents to their kids. But just because you, your partner, or one of your children might have allergies doesn’t mean that all of your kids will definitely get them. And someone usually doesn’t inherit a particular allergy, just the likelihood of having allergies.

Some kids have allergies even if no family member is allergic, and those who are allergic to one thing are likely to be allergic to others.

What Things Cause Allergies?

Common Airborne Allergens

Some of the most common things people are allergic to are airborne (carried through the air):

  • Dust mites are microscopic insects that live all around us and feed on the millions of dead skin cells that fall off our bodies every day. They’re the main allergic component of house dust. Dust mites are present year-round in most parts of the United States and live in bedding, upholstery, and carpets.
  • Pollen is a major cause of allergies (a pollen allergy is often called hay fever or rose fever). Trees, weeds, and grasses release these tiny particles into the air to fertilize other plants. Pollen allergies are seasonal, and the type of pollen someone is allergic to determines when symptoms happen.
    Pollen counts measure how much pollen is in the air and can help people with allergies predict how bad their symptoms might be on any given day. Pollen counts are usually higher in the morning and on warm, dry, breezy days, and lowest when it’s chilly and wet.
  • Molds are fungi that thrive both indoors and outside in warm, moist environments. Outdoors, molds can be found in poor drainage areas, such as in piles of rotting leaves or compost piles. Indoors, molds thrive in dark, poorly ventilated places such as bathrooms and damp basements. Molds tend to be seasonal, but some can grow year-round, especially those indoors.
  • Pet allergens are caused by pet dander (tiny flakes of shed skin) and animal saliva. When pets lick themselves, the saliva gets on their fur or feathers. As the saliva dries, protein particles become airborne and work their way into fabrics in the home. Pet urine also can cause allergies in the same way when it gets on airborne fur or skin, or when a pet pees in a spot that isn’t cleaned.
  • Cockroaches are also a major household allergen, especially in inner cities. Exposure to cockroach-infested buildings may be a major cause of the high rates of asthma in inner-city kids.

Common Food Allergens

Up to 2 million, or 8%, of kids in the United States are affected by food allergies. Eight foods account for most of those: cow’s milk, eggs, fish and shellfish, peanuts and tree nuts, soy, and wheat.

  • Cow’s milk (or cow’s milk protein). Between 2% and 3% of children younger than 3 years old are allergic to the proteins found in cow’s milk and cow’s milk-based formulas. Most formulas are cow’s milk-based. Milk proteins also can be a hidden ingredient in prepared foods. Many kids outgrow milk allergies.
  • Eggs. Egg allergy can be a challenge for parents. Eggs are used in many of the foods kids eat — and in many cases they’re “hidden” ingredients. Kids tend to outgrow egg allergies as they get older.
  • Fish and shellfish. These allergies are some of the more common adult food allergies and ones that people usually don’t outgrow. Fish and shellfish are from different families of food, so having an allergy to one does not necessarily mean someone will be allergic to the other.
  • Peanuts and tree nuts. Peanut allergies are on the rise, and as are allergies to tree nuts, such as almonds, walnuts, pecans, hazelnuts, and cashews. Most people do not outgrow peanut or tree nut allergies.
  • Soy. Soy allergy is more common among babies than older kids. Many infants who are allergic to cow’s milk are also allergic to the protein in soy formulas. Soy proteins are often a hidden ingredient in prepared foods.
  • Wheat. Wheat proteins are found in many foods, and some are more obvious than others. Although wheat allergy is often confused with celiac disease, there is a difference. Celiac disease is a sensitivity to gluten (found in wheat, rye, and barley). But a wheat allergy can do more than make a person feel ill — like other food allergies, it also can cause a life-threatening reaction.

Other Common Allergens

  • Insect allergy. For most kids, being stung by an insect means swelling, redness, and itching at the site of the bite. But for those with insect venom allergy, an insect sting can cause more serious symptoms.
  • Medicines. Antibiotics are the most common type of medicines that cause allergic reactions. Many other others, including over-the-counter medicines (those you can buy without a prescription), also can cause allergic reactions.
  • Chemicals. Some cosmetics or laundry detergents can make people break out in hives. Usually, this is because someone has a reaction to the chemicals in these products, though it may not always be an allergic reaction. Dyes, household cleaners, and pesticides used on lawns or plants also can cause allergic reactions in some people.

Some kids also have what are called cross-reactions. For example, kids who are allergic to birch pollen might have symptoms when they eat an apple because that apple is made up of a protein similar to one in the pollen. And for reasons that aren’t clear, people with a latex allergy (found in latex gloves and some kinds of hospital equipment) are more likely to be allergic to foods like kiwi, chestnuts, avocados, and bananas.

What Are the Signs and Symptoms of Allergies?

The type and severity of allergy symptoms vary from allergy to allergy and person to person. Allergies may show up as itchy eyes, sneezing, a stuffy nose, throat tightness, trouble breathing, vomiting, and even fainting or passing out.

Kids with severe allergies (such as those to food, medicine, or insect venom) can be at risk for a sudden, potentially life-threatening allergic reaction called anaphylaxis. Anaphylaxis can happen just seconds after being exposed to an allergen or not until a few hours later (if the reaction is from a food).

So doctors will want anyone diagnosed with a life-threatening allergy to carry an epinephrine auto-injector in case of an emergency. Epinephrine works quickly against serious allergy symptoms; for example, it reduces swelling and raises low blood pressure.

Airborne Allergy Symptoms

Airborne allergens can cause something known as allergic rhinitis, which usually develops by 10 years of age, reaches its peak in the teens or early twenties, and often disappears between the ages of 40 and 60.

Symptoms can include:

  • sneezing
  • itchy nose and/or throat
  • stuffy nose
  • coughing

When symptoms also include itchy, watery, and/or red eyes, this is called allergic conjunctivitis. (Dark circles that sometimes show up around the eyes are called allergic “shiners.”)

Food, Medicines, or Insect Allergy Symptoms

  • wheezing
  • trouble breathing
  • coughing
  • hoarseness
  • throat tightness
  • stomachache
  • vomiting
  • diarrhea
  • itchy, watery, or swollen eyes
  • hives
  • swelling
  • a drop in blood pressure, causing lightheadedness or loss of consciousness

Allergic reactions can vary. Sometimes, a person can have a mild reaction that affects only one body system, like hives on the skin. Other times, the reaction can be more serious and involve more than one part of the body. A mild reaction in the past does not mean that future reactions will be mild.

How Are Allergies Diagnosed?

Some allergies are fairly easy to identify but others are less obvious because they can be similar to other conditions.

If your child has cold-like symptoms lasting longer than a week or two or develops a “cold” at the same time every year, talk with your doctor, who might diagnose an allergy and prescribe medicines, or may refer you to an allergist (a doctor who is an expert in the treatment of allergies) for allergy tests.

To find the cause of an allergy, allergists usually do skin tests for the most common environmental and food allergens. A skin test can work in one of two ways:

  1. A drop of a purified liquid form of the allergen is dropped onto the skin and the area is scratched with a small pricking device.
  2. A small amount of allergen is injected just under the skin. This test stings a little but isn’t painful.

After about 15 minutes, if a lump surrounded by a reddish area (like a mosquito bite) appears at the site, the test is positive.

Blood tests may be done instead for kids with skin conditions, those who are on certain medicines, or those who are very sensitive to a particular allergen.

Even if testing shows an allergy, a child also must have symptoms to be diagnosed with an allergy. For example, a toddler who has a positive test for dust mites and sneezes a lot while playing on the floor would be considered allergic to dust mites.

How Are Allergies Treated?

There’s no cure for allergies, but symptoms can be managed. The best way to cope with them is to avoid the allergens. That means that parents must educate their kids early and often, not only about the allergy itself, but also about the reactions they can have if they consume or come into contact with the allergen.

Telling all caregivers (childcare staff, teachers, family members, parents of your child’s friends, etc.) about your child’s allergy is also important.

If avoiding environmental allergens isn’t possible or doesn’t help, doctors might prescribe medicines, including antihistamines, eye drops, and nasal sprays. (Many of these also are available without a prescription.)

In some cases, doctors recommend allergy shots (immunotherapy) to help desensitize a person to an allergen. But allergy shots are only helpful for allergens such as dust, mold, pollens, animals, and insect stings. They’re not used for food allergies.

Airborne Allergies

To help kids avoid airborne allergens:

  • Keep family pets out of your child’s bedroom.
  • Remove carpets or rugs from your child’s room (hard floors don’t collect dust as much as carpets do).
  • Don’t hang heavy drapes and get rid of other items that allow dust to build up.
  • Clean when your child is not in the room.
  • Use special covers to seal pillows and mattresses if your child is allergic to dust mites.
  • If your child has a pollen allergy, keep the windows closed when pollen season is at its peak, have your child take a bath or shower and change clothes after being outdoors, and don’t let him or her mow the lawn.
  • Keep kids who are allergic to mold away from damp areas, such as some basements, and keep bathrooms and other mold-prone areas clean and dry.

Food Allergies

Kids with food allergies must completely avoid products made with their allergens. This can be tough as allergens are found in many unexpected foods and products.

Always read labels to see if a packaged food contains your child’s allergen. Manufacturers of foods sold in the United States must state in understandable language whether foods contain any of the top eight most common allergens. This label requirement makes things a little easier. But it’s important to remember that “safe” foods could become unsafe if food companies change ingredients, processes, or production locations.

Cross-contamination means that the allergen is not one of the ingredients in a product, but might have come into contact with it during production or packaging. Companies are not required to label for cross-contamination risk, though some voluntarily do so. You may see statements such as “May contain…,” “Processed in a facility that also processes…,” or “Manufactured on equipment also used for ….”

Because products without such statements also might be cross-contaminated and the company did not label for it, it’s always best to contact the company to see if the product could contain your child’s allergen. Look for this information on the company’s website or email a company representative.

Cross-contamination also can happen at home or in restaurants when kitchen surfaces or utensils are used for different foods.

Reviewed by: Jordan C. Smallwood, MD Date reviewed: October 2016

Allergy Overview

What are allergies?

Allergies are your body’s reaction to a substance it views as a harmful “invader.” For example, coming into contact with what is normally a harmless substance, such as pollen, might cause the immune system (the body’s defense system) to react. Substances that cause these reactions are called allergens.

What is an allergic reaction?

An “allergic reaction” is the way the body responds to the allergen. A chain of events occur that result in an allergic reaction.

The first time an allergy-prone person is exposed to a specific allergen (such as pollen), the body responds by producing allergic (IgE) antibodies. The job of these antibodies is to find molecules of the offending substance in the bloodstream and tissues and to usher them to the body’s mast cells (a type of white blood cell) for destruction. As the mast cells destroy the allergens, a chemical called histamine is released into the bloodstream. A large amount of histamine swells body tissues (inflammation), causes itching, enlarges blood vessels, increases secretions, and causes bronchospasm (tightening of muscles that surround the airways).

What are the types of allergies and how are they treated?

People can be allergic to a wide variety of substances; the most common are pollen and dust mites. Other airborne allergens include molds and animal dander.


Seasonal allergic rhinitis, or hay fever, is an allergic response to pollen. It causes inflammation and swelling of the lining of the nose and of the protective tissue of the eyes (conjunctiva).

Symptoms include sneezing, congestion (feeling stuffy), and itchy, watery eyes. Treatment options include over-the-counter and prescription antihistamines, anti-leukotrienes, nasal steroids, and nasal cromolyn. Some people may have allergic asthma symptoms (wheezing, shortness of breath, chest tightness) caused by exposure to pollen.

Symptoms can be reduced by avoiding pollen. Stay indoors when pollen counts are high, close windows, and use air conditioning. Immunotherapy (“allergy shots”) also may be used to treat pollen allergy.

Dust mites

Dust mites are tiny organisms that live in dust and in the fibers of household objects, such as pillows, mattresses, carpet, and upholstery. Dust mites especially love warm, humid areas.

The symptoms of dust mite allergy are similar to those of pollen allergy. To help manage dust mite allergies, try using dust mite encasements (airtight plastic/polyurethane covers) over pillows, mattresses, and box springs. Also, remove carpet, or vacuum frequently with a high-efficiency filter vacuum cleaner. Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance methods and medications.


Molds are parasitic, tiny fungi (like Penicillium) with spores that float in the air like pollen. Mold is a common trigger for allergies. Mold can be found indoors in damp areas, such as the basement or bathroom, as well as outdoors in grass, leaf piles, hay, mulch, or under mushrooms. Mold spores reach a peak during hot, humid weather.

Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance and medications.

Animal dander

Allergic reactions can be caused by the proteins secreted by sweat glands in an animal’s skin, which are shed in dander, and (to a lesser extent) by the proteins in an animal’s saliva. Avoidance measures don’t work as well as simply removing the pet from the home. However, because many people are reluctant to do this, second-best measures include keeping the pet out of the bedroom, using air cleaners with HEPA filtration, and washing the pet (cat or dog) frequently.

Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance methods and medications.

Other allergens include:


Some people can develop a latex allergy after repeated contact with latex. Rubber gloves, such as those used in surgery or home cleaning, are a major source for causing this type of reaction. Skin rash, hives, eye tearing and irritation, wheezing, and itching of the skin may occur in people with latex allergy.

Allergic reactions to latex can be mild, such as skin redness and itching. More severe reactions can occur if the mucosal membranes are exposed, such as during an operation or a dental or gynecologic exam.

Treatment of latex reactions begins by removing the offending latex product. If you have latex allergy, it is important for you to wear a Medic Alert bracelet and carry an emergency epinephrine kit. All procedures should be carried out in a “latex-safe” fashion. There is no cure for latex allergy, so the best treatment for this condition is prevention.

Certain foods

Food allergies develop when the body develops a specific antibody to a specific food. An allergic reaction occurs within minutes of eating the food, and symptoms can be severe. In adults, the most common food allergies are shellfish, peanuts, and tree nuts; in children, they include milk, egg, soy, wheat, shellfish, peanuts, and tree nuts.

Symptoms of food allergy include itching, hives, nausea, vomiting, diarrhea, breathing difficulties, and swelling around the mouth.

The only treatment is to avoid the foods that cause allergy symptoms. If you (or your child) have a food allergy, your doctor may prescribe injectable epinephrine (adrenaline) for you to carry at all times. This is necessary in case foods that cause allergies are accidently eaten.

Insect venom (stings)

In a bee sting, the bee usually injects a sac of venom and may leave a stinger in the victim’s skin. If the stinger is still in the skin, gently scrape it out with a fingernail or a stiff-edged object like a credit card. Do not pull on the stinger, as this will cause the release of more venom into the skin.

A normal reaction will result in pain, swelling, and redness around the sting site. A large, local reaction may occur that will result in swelling that extends beyond the sting site. For example, a person stung on the ankle may have swelling of the leg.

The most serious reaction to an insect sting is an allergic one, which needs immediate medical attention. Symptoms of an allergic reaction to an insect sting include:

  • Difficulty breathing.
  • Generalized (widespread) hives that appear as a red, itchy rash that spreads to areas other than the area that was stung.
  • Swelling of the face, throat, or mouth tissue.
  • Wheezing or difficulty swallowing.
  • Restlessness and anxiety.
  • Rapid pulse.
  • Dizziness or a sharp drop in blood pressure.

If the patient has a reaction like this, a re-sting can cause a serious reaction that can be life-threatening.

An allergic reaction is treated with epinephrine (adrenaline). Anyone who has had allergic reactions from bee stings should be seen by a board-certified allergy/immunology doctor to confirm by skin and/or blood testing to bee venom that they have an allergy. Venom immunotherapy is recommended when venom allergy is confirmed. This will help reduce the possibility that a re-sting will cause a serious reaction.

What is allergic rhinitis?

Nasal allergy symptoms and hay fever are referred to as “allergic rhinitis.” Seasonal allergic rhinitis is nasal allergies that change with the seasons because of pollen from plants (trees, grasses, or weeds). Seasonal symptoms arise during the pollinating seasons for particular plants. Because you can be allergic to more than one thing, your symptoms may get worse at different times throughout the year, or may be constant.

Does everyone get allergies?

No. Most allergies are inherited, which means they are passed on to children by their parents. People inherit a tendency to be allergic, although not to any specific allergen. If a child develops an allergy, it is very likely that at least one of his or her parents has allergies.

How common are allergies?

More than 50 million Americans (1 in 6) suffer from all types of allergies, including indoor/outdoor allergies, food and drug, latex, insect, skin and eye allergies. The number of people who have allergies continues to increase across all ages, sex, and racial groups.

What are the symptoms of allergies?

Allergy symptoms can be classified as mild, moderate, or severe:

  • Mild reactions include local symptoms (affecting a specific area of the body) such as a rash or hives; itchiness, watery/red eyes, hay fever, and runny nose. Mild reactions do not spread to other parts of the body.
  • Moderate reactions include symptoms that spread to other parts of the body. Symptoms may include itchiness, hives, and/or swelling, and trouble breathing.
  • A severe allergic reaction, known as anaphylaxis, is a rare, life-threatening emergency in which the body’s response to the allergen is sudden and affects the whole body. Anaphylaxis may begin with severe itching of the eyes or face. Within minutes, more serious symptoms appear, including throat swelling (which could cause problems with swallowing and breathing); abdominal pain; cramps; vomiting; diarrhea; hives; and swelling (angioedema). The person may also have mental confusion or dizziness, since anaphylaxis may cause a drop in blood pressure.

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Allergies and the Immune System

Allergic disease is one of the most common chronic health conditions in the world. People with a family history of allergies have an increase risk of developing allergic disease. Hay fever (allergic rhinitis), eczema, hives, asthma, and food allergy are some types of allergic diseases. Allergy symptoms can range from mild to a serious, life-threatening allergic reaction (anaphylaxis).

Allergic reactions begin in your immune system. When a harmless substance such as dust, mold, or pollen is encountered by a person who is allergic to that substance, the immune system may over react by producing antibodies that “attack” the allergen. The can cause wheezing, itching, runny nose, watery or itchy eyes, and other symptoms.

What is the immune system?

The purpose of the immune system is to defend itself and keep microorganisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious microorganisms that do invade the body. The immune system is made up of a complex and vital network of cells and organs that protect the body from infection.

The organs involved with the immune system are called the lymphoid organs. They affect growth, development, and the release of lymphocytes (a type of white blood cell). The blood vessels and lymphatic vessels are important parts of the lymphoid organs. They carry the lymphocytes to and from different areas in the body. Each lymphoid organ plays a role in the production and activation of lymphocytes.

Lymphoid organs include:

  • Adenoids (two glands located at the back of the nasal passages)

  • Appendix (a small tube that is connected to the large intestine)

  • Blood vessels (the arteries, veins, and capillaries through which blood flows)

  • Bone marrow (the soft, fatty tissue found in bone cavities)

  • Lymph nodes (small organs shaped like beans, which are located throughout the body and connect via the lymphatic vessels)

  • Lymphatic vessels (a network of channels throughout the body that carries lymphocytes to the lymphoid organs and bloodstream)

  • Peyer’s patches (lymphoid tissue in the small intestine)

  • Spleen (a fist-sized organ located in the abdominal cavity)

  • Thymus (two lobes that join in front of the trachea behind the breast bone)

  • Tonsils (two oval masses in the back of the throat)

How does a person become allergic?

Allergens can be inhaled, ingested, or enter through the skin. Common allergic reactions, such as hay fever, certain types of asthma, and hives are linked to an antibody produced by the body called immunoglobulin E (IgE). Each IgE antibody can be very specific, reacting against certain pollens and other allergens. In other words, a person can be allergic to one type of pollen, but not another. When a susceptible person is exposed to an allergen, the body starts producing a large quantity of similar IgE antibodies. The next exposure to the same allergen may result in an allergic reaction. Symptoms of an allergic reaction will vary depending on the type and amount of allergen encountered and the manner in which the body’s immune system reacts to that allergen.

Allergies can affect anyone, regardless of age, gender, race, or socioeconomic status. Generally, allergies are more common in children. However, a first-time occurrence can happen at any age, or recur after many years of remission. Hormones, stress, smoke, perfume, or environmental irritants may also play a role in the development or severity of allergies.

What is anaphylactic shock?

Anaphylactic shock, also called anaphylaxis, is a severe, life-threatening reaction to certain allergens. Body tissues may swell, including tissues in the throat. Anaphylactic shock is also characterized by a sudden drop in blood pressure. The following are the most common symptoms of anaphylactic shock. However, each person may experience symptoms differently. Other symptoms may include:

  • Itching and hives over most of the body

  • Feeling warm

  • Swelling of the throat and tongue or tightness in throat

  • Difficulty breathing or shortness of breath

  • Dizziness

  • Headache

  • Pain or cramps

  • Nausea, vomiting, or diarrhea

  • Shock

  • Loss of consciousness

  • Feeling light-headed

  • Anxiety

  • Abnormal heart rate (too fast or too slow)

Anaphylactic shock can be caused by an allergic reaction to a drug, food, serum, insect venom, allergen extract, or chemical. Some people who are aware of their allergic reactions or allergens carry an emergency anaphylaxis kit that contains injectable epinephrine (a drug that stimulates the adrenal glands and increases the rate and force of the heartbeat).

For information about food allergies please visit the following pages:

  • Food allergy

  • Food allergies in children

What Causes Allergies? The Role of Antibodies:

The immune system is similar to a sensory system in that it receives input from the environment and produces an adaptive response. Its purpose is to recognize foreign invaders, such as bacteria and parasites, and launch an attack to neutralize the threat of infection. It also recognizes and disposes of ill or defective internal cells, to prevent a disease from spreading.

The way the immune system accomplishes this is by recognizing what is foreign or abnormal, and separating it from what is normal. This is done through a complex process that produces millions of unique antibodies which serve as recognition agents that can trigger an immune response.

After an antibody becomes activated through recognition/interaction with a foreign protein it is then mass produced by immune cells and circulates the body to form an immunological memory. This is how vaccinations work, where exposure to weakened or partial components of disease-causing microbes allows the body to prepare itself for launching a large immune response when the microbe is encountered in the future.

During production by the immune system, these antibodies are supposed to be edited to remove ones that attack the self. In cases where this does not occur, autoimmune disorders, such as multiple sclerosis, result. In cases where the antibodies react to non-threatening proteins, such as those found in grass pollen, then allergy results. In a sense, allergy can be thought of as one extreme on a spectrum that has autoimmune disorders on the other. Health is the balance between the two where the immune response is always appropriate and controlled.

How Do Allergies Evolve?
Allergic disease and autoimmune disorders occur because the immune system gets conditioned to respond to inappropriate targets. If it attacks the body, it is an autoimmune disorder, and if it attacks a harmless environmental protein, then it is an allergy. In the case of allergy, pollen seasons can produce an enormous immune response because of the significant amount of exposure. Interestingly, these problems appear to be much more common in wealthy, industrialized nations. One theory about why this occurs is called the Hygiene Hypothesis.

In population studies, prevalence of allergy is low in developing countries, which lack the advanced sanitation found in wealthy countries. This lack of sanitation leads to an early exposure to parasites and other microbes that is likely similar to what humans have experienced over centuries of evolution. Since our immune systems evolved over long periods of time under constant exposure to microbes, if those microbes are removed, the system’s potential is still active but no longer has a suitable target.

Studies have shown that early immune system exposure to parasites and other microbes allows the system to develop the regulatory mechanisms that keep it focused and under control. In the normal course of childhood development, the immune system is supposed to shift away from the anti-parasitic inflammatory pathway predominant at birth toward the anti-bacterial non-inflammatory pathway. In clean environments that lack parasite exposure, this transition fails to occur and the child predisposed to allergy begins to develop an inflammatory immune response against harmless environmental proteins.

This is not to romanticize unsanitary conditions, of course. Though rates of allergy are low in developing countries, rates of preventable diseases are much higher. This suggests that biological systems require balance, where overcorrection from one problem has unforeseen negative consequences.

What makes some people susceptible to allergies?

Why some people are allergic to certain things while others are not can be a difficult topic to understand. For example, a dog can jump into your lap and, just like that, you will start to sneeze and your eyes will drip. All of this will force you to toss Fido aside in search of a tissue box. Meanwhile, your friend or neighbor experiences none of the above effects.

Why is this? Why are some people more susceptible to allergies than others? This article will help you understand why allergies target some more than others.


It’s in the Genes

Allergies can often be blamed on mom and dad. The tendency to become allergic is inherited, and the chances that you also will be allergic increase from about 50 percent when one parent is allergic to 75 to 80 percent when both parents have allergies.

Tell your friends you’re “atopic,” meaning that you have inherited the tendency to have an allergy. (And hope that none of your friends know Greek, as “atopic” derives from the Greek word for “strange.”) But you needn’t feel strange…or alone. The American College of Allergy, Asthma and Immunology (ACAAI) estimates that as many as 50 million Americans suffer with asthma, hay fever, or other allergy-related conditions.

So, the family genes are stacked against you. Does this mean instant sniffles? Not always. Don’t forget, even if you have a 60 percent chance of developing allergies, you also have a 40 percent chance of not developing them. That’s why Fido turns your nose and eyes into streams while your brother is pretty much dry. In the genetic roll of dice, he came out the winner.

On the next page, learn about allergies in the environment.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

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From the Allergic Living Archives. First published in 2008.

If you have a child with peanut allergies, other parents will say to you: “Nobody was allergic to peanut butter when I was a kid.” If a cat swishing through a room starts you wheezing, you’ll get asked: “How come so many people have asthma?”

Both are reasonable questions, variants on the broader million-dollar one: “Why do so many people have allergies today?”

If you want an easy answer, allergy experts will simply say they don’t know. But what they mean is – they don’t know entirely. The fact is that scientists understand a lot more about allergic disease than they did a decade ago. There are still gaping holes in their knowledge, but as they continue to fill in the pieces to the puzzle, what they are finding is fascinating and often surprising. In the following investigation, Allergic Living examines what science knows so far about why allergies occur.

In the Beginning

When a baby is born, its immune system is a work in progress. “You’re born with a naive, allergic-skewed immune system,” explains Dr. Michael Cyr, an allergist and immunologist at McMaster University in Hamilton, Canada. This is what scientists call the Th2 mode.

During the first days, weeks and months of life, as the baby comes into contact with various germs, bacteria, viruses and infection. The immune system is supposed to start learning to distinguish between what is harmful and what is benign.

Some allergists liken the emerging immune system to a toggle switch or a reset button. We’re all born in that Th2 mode and then that first bout of sniffles at eight weeks or the ear infection at four months begins to “switch” the immune system over from Th2 to Th1 mode or fighting bacterial infection mode.

But in the person with a genetic inclination to allergy, something misfires and the switchover doesn’t happen properly. Cyr, who’s a researcher with AllerGen (the Allergy, Genes and Environment Network), says that why this process happens easily for some people but not for others remains unclear, and may depend on a confluence of factors.

The young child who doesn’t get switched over is now atopic – predisposed to developing an allergic response to a trigger such as cat dander or ragweed pollen or peanuts. After breathing in or consuming one of those, the child’s immune system creates allergy antibodies – specifically Immunoglobulin E or IgE antibodies – to guard against the offending trigger. The next time the immune system encounters it, the IgE will go on the defensive, setting off a cascade of allergic symptoms.

Though genetics are a large contributing factor to whether a person becomes allergic, scientists haven’t found one specific allergy gene. “It’s becoming clear that it’s not a gene, it’s a whole series of genes,” says Cyr. Something has changed to increase the number of us who are developing allergies, says Dr. Dennis Ownby, a professor of pediatrics and the head of allergy and immunology at the Medical College of Georgia in Augusta.

“What seems to have happened over the last three decades, at least in developed countries, is that genetic ability has become more prominent,” he says.

Just how much have allergies and asthma grown? Figures from the World Allergy Organization reveal the global prevalence of asthma has increased by an astounding 50 per cent every decade for the past 40 years. In North America today, leading allergy organizations estimate that about 24 million Americans and three million Canadians have asthma.

In the past decade alone, the prevalence of food allergy, once an uncommon condition, has skyrocketed. Prevalence studies estimate that about 15 million* Americans, along with 2.5 million Canadians, now contend with the disease.

In our modern world, allergy has spread like wildfire. Scientists are certain that genes alone can’t be the whole reason why. “The genetic pool does not dramatically change over decades,” notes Cyr. “So it’s obvious there’s something else going on.” And that something appears to be our environment.

Getting to the Dirt

While references to asthma date back to ancient Chinese medical texts, the real story of our modern understanding of allergy begins in earnest in 1989. It was a heady year, with the fall of Berlin Wall and the beginning of the opening up of the former East bloc. A team of German scientists decided this presented a great opportunity to compare the prevalence of asthma in Leipzig (former East Germany) and Munich (former West Germany).

Here were two highly similar gene pools of people who had been living in very different societies and conditions. “At that stage, everyone, including us, believed that air pollution was causing asthma and allergies,” says Dr. Erika von Mutius, who was then a young pediatrician and team leader, and who today is a professor and head of the asthma and allergy department of Munich University’s Children’s Hospital.

When the findings began coming back showing that there was considerably more asthma in modern, Western, hygienic Munich than among the study group living in Leipzig with its billowing factory smokestacks, the researchers were incredulous.

“It was so opposite what we’d anticipated,” recalls von Mutius on the phone from Munich. “We didn’t believe it, so we thought it was a mistake in data entry and re-entered all the data.” But the data were right, and the results were published in 1992.

That year, von Mutius took her research with her to Tuscon, Arizona, where she worked on a fellowship at the University of Arizona under her mentor, Dr. Fernando Martinez, the well-known asthma researcher who today is the director of the Arizona Respiratory Center. One day he read a medical paper out of Britain about something called “the hygiene hypothesis”.

The author of that paper, an epidemiologist named David Strachan, had conducted a study of over 17,000 British children and found that youngsters who had older siblings and were exposed to more infections and bacteria early in life were less likely to develop hay fever or eczema. Writing in that same pivotal year of 1989, Strachan had theorized that smaller family sizes and higher levels of hygiene in modern Western homes may have been contributing directly to the increased prevalence of allergy.

Martinez was intrigued. What, he asked, would happen if von Mutius took into account the sizes of her East German and West German families? The data were incomplete, but it was the less allergic East Germans who clearly had more children per family. She and Martinez followed up with a study comparing family sizes and allergy in Munich and Leipzig (and a neighboring city).

A pattern emerged: the most allergic were the Munich kids with one or no siblings; the least allergic were the East Germans with two or more brothers and sisters. Children in the larger families were being exposed to more germs. It fit with this rudimentary hygiene hypothesis. “It took off from there,” says von Mutius.

Back to the Land

Where the hygiene theory took off to was a place caught in a time warp: the traditional European farm, where father, mother and children still do all the manual labor, from milking to sweeping out the stables. The idea to look at the family-run farm actually came from a school doctor in a Swiss village. He noticed that farm children under his care, unlike other kids, never seemed to get hay fever.

Struck by this observation, he began writing to allergy experts in Basel, research colleagues of von Mutius. At first they were skeptical of the rural doctor’s notion, but then a few Swiss professors ran a small study. The findings were compelling: there was markedly less allergy and asthma on the farms in question. This merited further examination.

And so in 1998, von Mutius began her long-running involvement in a series of European farm studies that have become the underpinning of current allergy research. The first was ALEX (the Allergy and Endotoxin Study), involving scientists from Germany, Austria and Switzerland. The team began gathering and publishing data, and the central findings were consistent: children who lived on these farms were significantly less inclined to have allergies and asthma than children in the neighboring village.

Then came other major studies of the family farms: the multi-center PARSIFAL study of children enrolled in Steiner schools (akin to Waldorf education), which involved 6,600 pupils in five countries; and the PASTURE study, which examined children’s exposure to microbes on farms across Europe. With each study, with each new set of samples of stable and mattress dust, with each new set of blood-test results for environmental and food allergies, a little more was known. “We are getting somewhere,” says von Mutius, taking stock for a moment. “There are now 17 papers that all show the same things.”

They reveal what’s termed “the farming effect,” a phenomenon that protects against allergic disease. Von Mutius and her colleagues have narrowed the effect down to three key factors: livestock (specifically cows, pigs or poultry); type of fodder (for instance, whether it’s fresh grass or hay); and drinking of raw farm milk.

The findings have been generally consistent – about 1 to 2 per cent of the farm children in the studies had asthma compared to 12 per cent of local, non-farm children in control groups. “I’m completely convinced that this is real,” says von Mutius. “The question is – are we going to be able to solve the puzzle.”

To that end, today von Mutius is co-leader of a massive European Commission project called GABRIEL, which involves 14 countries and 40,000 test subjects. Among its goals is to identify what in those three key elements of livestock, fodder and unpasteurized milk confers protection against allergy, whether it acts alone or in combination with other farm factors as well as the genetic background, and how this all takes place.

For a while, some thought a key was endotoxin in the barns – that’s the membrane of certain bacteria that stimulates the immune system and can cause illness. But fungal spores are also proving important. At this stage, von Mutius finds endotoxin a minor player. “It’s not just endotoxin. We think it is microbial factors on the farms – it’s probably anything that’s bacterial, or molds, maybe yeasts. We’re trying to develop new tools to measure those exposures.”

While her researchers are dealing in microscopic levels and minute interactions, von Mutius remains keenly aware of the bigger picture, of the “why” of allergies.

“Mankind has evolved with farm animals for thousands of years, and so probably there is an evolutionary system here that tells the immune system – ‘this is normal,’” she says. “Maybe that’s something the immune system needs in order to know that – this is harmless, this is nothing that needs to be recognized. In the absence of these factors, all of a sudden these proteins are being recognized as foreign where the immune system starts to mount an IgE response.”

Timing is Everything

What also appears to be important is when a child is first exposed to an environment that affords protection against allergies. It seems the earlier, the better. In 2001, the journal The Lancet published ALEX research in which children who were exposed to farm life from birth to age 5 were tested for allergies. Those children’s results were compared to levels from children who first came to live on a farm between the ages of 1 and 5. The most protected by far were the children who had lived on farms all of their lives until the age of 5, with fewer than 1 per cent developing either asthma or hay fever.

Von Mutius and her colleagues have deduced that the protective “farming effect” begins even before the baby is born. On the traditional farms, women continue to do chores through pregnancy, spending much time in the barn and around cattle. The exposure to the protective stimuli “already starts in utero, and we think the first two years in life are the most important ones,” says von Mutius.

Evidence of immunity before birth could be clearly seen in the umbilical cord blood of 922 babies in the five-country PASTURE study. The blood belonging to the farm babies was much less likely to contain allergy-causing antibodies to airborne triggers such as grass.

A consensus is forming around the importance of cord blood to allergy research. Back across the Atlantic, Cyr has been focusing on this at the McMaster University Medical Centre. His findings indicate that “the more allergic that mothers are, the less mature the cord blood’s stem cells appear to be in terms of the receptors that are important to the Th2-Th1 switch.” This could be a clue to future allergic status.

“It may well be that cord-blood stem cells are a marker,” Cyr says. They could indicate that “even from the day allergic kids are born, their immune systems are already less mature than kids from non-allergic parents.”

Umbilical cord blood will be examined in as many as 5,000 Canadian babies as part of the CHILD (Canadian Healthy Infant Longitudinal Development) study that recently received $12 million in funding from the Canadian government and AllerGen. The four-city study is designed to follow this group of children from pregnancy to the age of 5, and the first-phase of the project is well underway in Vancouver.

Dr. Stuart Turvey leads that pilot project, nicknamed Mini-CHILD, and he speaks excitedly about the prospect of having access to the cord blood of so many children and seeing “the quality of the immune response on the day the babies are born.” A pediatric allergist-immunologist at the University of British Columbia and B.C. Children’s Hospital, he, too, views the period from fetal development in the womb to 2 years of age as crucial, even in those individuals who don’t develop allergies until later.

What is in an Environment?

The primary interest of the big Canadian study is to identify environmental factors in urban living that put children at greater risk for allergies and asthma. In conversation, people tend to use the word “environment” as a catchall for the great outdoors and pollution or perhaps to mean one’s living space. But to epidemiologists and immunologists it’s much more. The womb, for instance, is one environment.

When Turvey speaks of the “environment” that the families enrolling in CHILD are exposed to, he breaks it down into several sub-categories. First, he sees the physical environments – the home, the daycare, the level of pollution outside them; the levels of dust, mold, tobacco smoke and chemical exposures inside; and whether pets are owned.

“And I think the infectious environment is important – factors such as cold viruses and bacteria in a baby’s body,” he says. He even views diet as another environment of stimuli that may influence immune responses: “environment is everything we’re exposed to.”

Turvey also describes a psycho-social environment, and here, he’s largely talking about the amount of stress on the mother in pregnancy or in the home after birth. Is there, for instance, a financial burden or might her support network be lacking?

“There’s evidence that stress can make asthma worse and may even set the scene for asthma predisposition in infants,” he says. He thinks these aspects, even in utero, “should not be underestimated.”

CHILD’s researchers are examining all the environments of the babies. They collect dust, mold, air and blood samples, and will retest at specified intervals for comparison. The researchers ask for the very first bowel movement of newborns in the study. This is no joke: they want to know what bacteria the brand new baby has in his gut, and then compare those bacteria to what’s found in the intestines over time, up until the age of 5. They are trying to understand, Turvey says: “Are there protective bacteria or bad bacteria?”

Bacterial exposures are fascinating if complicated. Dr. Malcolm Sears, the epidemiologist who is director of the CHILD project, explains that how a person’s immune system will respond to a given bacteria will vary, and may depend on which bacteria and the quantity involved. “Certain genetic structures may make a substance like endotoxin, for instance, protective in some people and increase allergies in others. It’s not neutral, it can go either way depending on the genetic background,” says Sears, who is a professor of medicine at McMaster University.

When we speak of “good” bacteria, probiotics leap to mind, those so-called “friendly” micro-organisms that are beneficial to the gastrointestinal system. Could introducing them to a diet contribute to allergy prevention? Von Mutius sees indications that probiotics “might work,” but says the definitive study has yet to be produced.

There is something more apparently protective about the raw milk in the European farm studies, but von Mutius and her team do not yet know precisely what bacteria are making a difference, or whether the heating and denaturating of proteins is at play. She is not promoting the drinking of untreated farm milk, noting there are good reasons for wanting to kill pathogens in such a dietary staple. However, pasteurization as we know it has had a good run; Louis Pasteur invented it back in the 1860s.

In future, there may be practical applications from the European findings about raw milk. “You don’t want the pathogens, but maybe there are other ways,” she says. “I think we need to be clever and creative and find ways to do it.”

Like the researchers in CHILD, she and her team consider the farms they’ve studied to be a specific environment. This is a cloistered and natural environment – a big Petri dish of microbes and clues from a time that’s largely passed. We can’t all go back to live on the farm, but this unique environment may divulge answers to help bring the allergy epidemic under control.

From Cows to Dogs

In the urban environment, of course, there is one similarity to the traditional farm. We do still live among animals: those we keep as pets. As news spread from the European farm studies that exposure to cows, pigs and poultry was helping to protect against allergic disease, scientists began to wonder – could this protection be elicited from non-working animals, specifically dogs and cats?

Dr. Dennis Ownby is one of the leading researchers in this area. In 2002, he and a team of researchers from Henry Ford Hospital published findings in the Journal of the American Medical Association that were surprisingly contrary to the long-held belief that pets in the home would lead infants to develop allergies.

Ownby’s group conducted a study of 474 healthy Detroit children from birth to age 6, examining how exposures to cats and dogs affected the participants’ rate of sensitization to common allergens, including the animals themselves, mold, ragweed, grass and dust mites. The results showed that when infants in the first year of life lived with two or more dogs (or dogs and cats in combination), their risk of developing allergies at 6 or 7 years old was less than half (15.4 per cent) that of kids who hadn’t had any pet exposure (33.6 per cent).

In an interview, Ownby said: “There is something about being around an animal that changes the immune system so that you’re less likely to be allergic to anything.” (However, what remains the case is that if an individual in a household develops pet allergies, the animal should be found a new home.)

The topic had been contentious, with some studies making the case for, and some against pets as protective against allergies. However lately, research on dog exposure in early life has been uniformly positive. For instance, scientists in Munich in 2008 examined data from 3,150 children in two large population studies. The results, published in the European Respiratory Journal, revealed that in blood tests at the age of 6, children who had dogs in their homes during the first year of birth showed markedly lower rates of sensitization to inhaled allergens, such as dust mites, cats, grass and birch pollen.

The findings with cats have been more inconsistent, though a 2007 study of New York City children saw some latent positive effects. Scientists from Columbia University found that kids who had infant exposure to cats were more likely to develop antibodies to the animals and wheeze by age 3. Yet, those same children showed signs of a protective effect and were less likely to wheeze by the time they had turned 5. The researchers suggest that prolonged exposure to cats may produce a tolerance to the allergen.

What’s clear from the published research is that if there is a protective benefit to pet ownership, as with livestock, it happens early in life.

Next: Allergy’s Relationship to Life in the Big City

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