Food allergies causing diarrhea

Food Problems: Is it an Allergy or Intolerance

What is a food allergy?

A food allergy is an immune system response. It is caused when the body mistakes an ingredient in food — usually a protein — as harmful and creates a defense system (antibodies) to fight it. An allergic reaction occurs when the antibodies are battling an “invading” food protein. The most common food allergies are shellfish, nuts, fish, eggs, peanuts, and milk.

What is food intolerance?

Food intolerance is a digestive system response rather than an immune system response. It occurs when something in food irritates a person’s digestive system or when a person is unable to properly digest, or break down, the food. Intolerance to lactose, which is found in milk and other dairy products, is the most common food intolerance.

How common are food allergies and intolerances?

Food allergies affect about 1 percent of adults and 7 percent of children, although some children outgrow their allergies. Food intolerances are much more common. In fact, nearly everyone at one time has had an unpleasant reaction to something they ate. Some people have specific food intolerances. Lactose intolerance, the most common specific food intolerance, affects about 10 percent of Americans.

How can you tell the difference between an allergy and intolerance to food?

Food allergies can be triggered by even a small amount of the food and occur every time the food is consumed. People with food allergies are generally advised to avoid the offending foods completely. On the other hand, food intolerances often are dose related; people with food intolerance may not have symptoms unless they eat a large portion of the food or eat the food frequently. For example, a person with lactose intolerance may be able to drink milk in coffee or a single glass of milk, but becomes sick if he or she drinks several glasses of milk. Food allergies and intolerances also are different from food poisoning, which generally results from spoiled or tainted food and affects more than one person eating the food. Your health care provider can help determine if you have an allergy or intolerance, and establish a plan to help control symptoms.

What are the symptoms of a food allergy?

Symptoms of a food allergy can range from mild to severe, and the amount of food necessary to trigger a reaction varies from person to person. Symptoms of a food allergy may include:

  • Rash or hives
  • Nausea
  • Cramping stomach pain
  • Diarrhea
  • Itchy skin
  • Shortness of breath
  • Chest pain
  • Swelling of the airways to the lungs

Anaphylaxis is a very serious and potentially fatal allergic reaction that involves a sudden drop in blood pressure, loss of consciousness and body system failure.

What are the symptoms of food intolerance?

Symptoms of food intolerance include:

  • Nausea
  • Stomach pain
  • Gas, cramps or bloating
  • Vomiting
  • Heartburn
  • Diarrhea
  • Headaches
  • Irritability or nervousness

What causes food allergies and intolerances?

Food allergies arise from sensitivity to chemical compounds (proteins) in food, even compounds that are found naturally in food. Food allergies are more common in people whose family members have allergies, suggesting a genetic — or hereditary — factor may be involved with the development of food allergies.

Food allergies develop after you are exposed to a food protein that your body thinks is harmful. The first time you eat the food containing the protein, your immune system responds by creating specific disease-fighting antibodies (called immunoglobulin E or IgE). When you eat the food again, it triggers the release of IgE antibodies and other chemicals, including histamine, in an effort to expel the protein “invader” from your body. Histamine is a powerful chemical that can affect the respiratory system, gastrointestinal tract, skin or cardiovascular system.

The allergy symptoms you have depend on where in the body the histamine is released. If it is released in the ears, nose and throat, you may have an itchy nose and mouth, or trouble breathing or swallowing. If histamine is released in the skin, you may develop hives or a rash. If histamine is released in the gastrointestinal tract, you likely will develop stomach pains, cramps or diarrhea. Many people experience a combination of symptoms as the food is eaten and digested.

There are many factors that may contribute to food intolerance. In some cases — as with lactose intolerance — the person lacks the chemicals, called enzymes, necessary to properly digest certain proteins found in food. Also common are intolerances to some chemical ingredients added to food to provide color, enhance taste and protect against the growth of bacteria. These ingredients include various dyes and monosodium glutamate (MSG), a flavor enhancer.

Substances called sulfites, which may occur naturally — as in red wines — or may be added to prevent the growth of mold, also are a source of intolerance for some people. The Food and Drug Administration has banned the use of spray-on sulfates to preserve fruits and vegetables, but sulfates are still found naturally in some foods. Salicylates are a group of plant chemicals found naturally in many fruits, vegetables, nuts, coffee, juices, beer and wine. Aspirin also is a compound of the salicylate family. Foods containing salicylates may trigger symptoms in people who are sensitive to aspirin. Of course, any food consumed in excessive quantities can cause digestive symptoms.

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A food allergy is an immune system response by which the body creates antibodies as a reaction to certain food. Symptoms similar to those of irritable bowel syndrome (IBS) include diarrhea and abdominal pain. Other symptoms can include vomiting, hives, itching, swelling of the lips, tightness in the throat, and wheezing. Allergic symptoms usually occur within a few minutes to an hour after ingesting the causative food. Eight foods cause 90% of all allergic reactions: milk, egg, wheat, peanuts, soy, tree nuts (almonds, walnuts, pecans, etc.), fish, and shellfish.

Food Allergies and Food Intolerance Tip:

Although relatively rare, food allergies to certain foods can also mimic or worsen symptoms of functional GI disorders. Allergies can also lead to more generalized symptoms involving skin rashes, asthma, and swelling.

Food intolerance occurs when the body cannot adequately digest a portion of a particular food, usually because of a chemical deficiency. Examples of food intolerance can include:

Lactose intolerance – People with this common disorder have difficulty digesting milk because of a deficiency of the enzyme lactase.

Congenital sucrase-isomaltase deficiency (CSID) – People this rare disorder cannot break down the sugars sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains).

In response to a mailed consumer questionnaire that surveyed 5,000 representative Americans, 16% reported conditions that they felt were food allergies. However, studies show that true food allergies are present in only 1-2% of adults. In people with IBS, reactions to food are rarely allergic reactions.

If a food allergy is suspected, the offending food should be eliminated from the diet and then reintroduced. If the symptoms improve on the elimination diet, and then consistently recur when the food is introduced back into the diet, formal allergy testing should be performed. Sometimes an elimination diet to exclude all known allergens can help distinguish food allergy from other symptoms.

Studies have shown that the onset of symptoms in a person can be influenced by even a mistaken belief that they have food allergies. Therefore, allergy testing is done to make a definitive diagnosis.

If you suspect you are intolerant to certain foods or that you have a food allergy, talk to your physician or consult a registered dietitian before making any drastic changes in your diet. You want to make sure you are maintaining proper nutritional balance in your diet and not disrupting your quality of life by needlessly eliminating certain beneficial foods.


Boan JF (Formerly Knowles). Dietary Factors in Gastrointestinal Diseases. IFFGD Fact Sheet No. 148; 1998.

For more information vist:

The Publications Library topics on food intolerance/malabsorption.

Food Allergy vs. Intolerance

Know the Difference

Understanding the difference between food allergies and food intolerances can leave a person justifiably confused. With these medical conditions having potential overlapping symptoms (e.g., cramps, upset stomach, diarrhea, skin rash, and headache), it is easy to see why the line separating the two is so often blurred.


Food allergy (also called hypersensitivity) involves an inappropriate immune reaction to a seemingly harmless, non-pathogenic substance. The body reacts to the substance as if it were fighting a disease-producing microorganism. On first exposure to the offending food, the body’s immune system produces antibodies called immunoglobin E (IgE), which are specific to that allergen. With any subsequent exposure, the allergen binds to the IgE antibodies, which triggers the immune system to initiate a more rapid and aggressive response. This intense reaction can produce oral inflammation, canker sores, cramps, nausea, diarrhea, gas, hives, and sometimes can produce respiratory distress.1

Symptoms can appear immediately after eating or could take several hours to appear and can range from mild to severe. The most severe reaction, anaphylactic shock, affects the whole body, with symptoms usually presenting within one hour following contact. Symptoms include wheezing, difficulty breathing, swelling of the throat and tongue, vomiting, and fainting. Anaphylaxis can be deadly and requires immediate medical attention.2 People with known allergies should carry an auto-injector of epinephrine, a medicine that counteracts the reaction, in case of exposure to the food.

Food allergies affect as many as 5-6% of young children and 3-4% of adults in Westernized countries.3 Allergies tend to run in families and are more common in children than they are in adults, as some children outgrow their food allergies over time. Allergies to eggs, milk, wheat, soy, and peanuts cause the most problems in children, while adults most often suffer from allergies to peanuts, tree nuts, fish, and shellfish.2


In contrast to food allergy, food intolerance does not involve the body’s immune system. Intolerance is an adverse reaction to a food, likely to originate in the gastrointestinal system, usually caused by a limited ability or an inability to digest or absorb certain foods or their components. Food intolerance symptoms usually begin about half an hour after eating or drinking the food in question, but in some circumstances may not appear for up to 48 hours. Symptoms include nausea, bloating, abdominal pain, and diarrhea. Two examples of food intolerance are:

  • Lactose Intolerance: Up to 70% of the world’s population is unable to consume milk or dairy products without getting an upset stomach.4 Typically, the human body can produce the enzyme lactase, which helps digest the sugar found in milk (lactose); however, people who are lactose intolerant do not produce a sufficient quantity of lactase and, therefore, digestion of milk-containing foods is not adequate. Undigested lactose lingers in the intestine and ferments, causing abdominal pain, bloating, diarrhea, and flatulence. For more information on lactose intolerance, contact our office.
  • Non-Celiac Gluten Intolerance: Although people with celiac disease must strictly abide by a gluten-free diet to prevent damage to their intestines, many non-celiac individuals are finding that avoiding gluten improves their gastrointestinal symptoms, hence the growing popularity of gluten-free foods. Despite limited scientific literature to prove its existence, this so-called “non-celiac gluten intolerance” or “wheat intolerance” is believed to be quite common.5 In one double-blind, randomized, placebo-controlled trial, patients reported that gluten induced symptoms of bloating, dissatisfaction with stool consistency, abdominal pain, and tiredness. There is no evidence that non-celiac gluten intolerance causes damage to the small intestine.6
Food Allergy Food Intolerance
Immune System Activated Yes No
Exposure Required to Elicit Symptoms Tiny quantity Normal size portion
Timeframe for Reaction After Exposure Immediate – 1 or 2 hrs 30 min – 48 hrs
Treatment Food avoidance, medicines (antihistamines, epinephrine shot) Food limitation or complete avoidance, depending on severity

On February 16, 2011 Health Canada published amendments to its Food Allergen Labelling Regulations. The current guidelines require that most pre-packaged foods carry a label and that the ingredients appear on labels in decreasing order of proportion. When the new amendments come into effect on August 4, 2012 some ingredients used in food products that were previously exempt will now be required to appear on food labels. It is Health Canada’s intention to make it simpler for those with food allergies, and sensitivities or intolerances, to avoid contact with an undeclared ingredient that could potentially lead to serious health consequences. For more information please visit Health Canada.

Want to learn more about allergy and intolerance?

We have several related articles that may be helpful:

  • 10 Myths about Food Allergies
  • Food Allergy vs. Intolerance
  • Gut Bacteria Protect Against Nut and Other Allergies
  • Intestinal Gas from Complex Carbohydrates or Lactose Intolerance
  • Is Your Gut Friend or Foe?
  • Shedding Light on Peanut Allergies
  • Yeast and Mould Allergy
First published in the Inside Tract® newsletter issue 178 – 2011
Image Credit: ©

How Do Food Allergies Affect Digestion?

Everyday Health: The rates of food allergies continue to rise. What are the most common food allergies, and how do they affect digestion?

Mark Babyatsky, MD (

Food allergies are estimated to affect 6 to 8 percent of children in the United States and 3 to 4 percent of adults. Many children who demonstrate allergy to milk protein outgrow them. In adults, shellfish, peanuts, tree nuts, fish, and egg are the most common. Of note, those with peanut and tree nut allergies are unlikely to outgrow them, including the recently increasingly prevalent sesame allergy. Symptoms are usually acute, but can be chronic and include the gamut of allergic responses in the entire body. In the digestive tract, symptoms include nausea, vomiting, abdominal pain, odynophagia (painful swallowing), diarrhea, or any combination of these symptoms.

Kenneth Brown, MD (

Many patients feel they are allergic to a food product because they had some sort of reaction after eating. Although adverse food reactions are common, true food allergies are only present in 3 — 4 percent of adults. An allergy is defined by having an adverse immune response to a food protein. One of the most common food allergies is an intolerance to gluten, known as celiac disease. Celiac disease is a common problem, affecting 1 in every 133 people in the United States. It is a lifelong autoimmune disorder in which the body creates a toxic response to the ingestion of any type of gluten. Gluten is the protein found in all forms of wheat, barley, rye, and some oats. This causes damage to the small intestine, which does not allow for absorption of essential nutrients and minerals into the body. Thus, celiac is classified as a disease of an autoimmune reaction to gluten.

More commonly, people have intolerances to foods, rather than allergies. An example of food intolerance is when someone has bloating and diarrhea after consuming lactose. These people have low levels of the enzyme lactase, which prevents the lactose sugar from being broken down.

Lisa Ganjhu, DO (

Some of the most common food allergies are peanuts, milk, soy, shellfish, fish, nuts, and eggs. Some people can have very severe reactions to those foods if they are allergic. The digestive tract is the first line of contact to food, so it is where allergic reactions originate. The gastrointestinal reaction is to rapidly get rid of or neutralize the irritant or the allergen. Common gastrointestinal reactions are abdominal pain, nausea, vomiting, and diarrhea.

Lisa Pichney, MD (

The eight most common food allergens are milk, wheat, soy, shellfish, fish, peanuts, tree nuts, and eggs. Celiac disease involves an allergy or sensitivity to gluten, which is found in wheat. Patients with celiac disease may malabsorb macronutrients and become ill.

Seth Rosen, MD (

While true allergies to food are often difficult to define, there are a variety of conditions that can cause intolerance of certain foods. Examples of this are lactose intolerance and celiac disease. Lactose intolerance is an inability to properly digest milk and other lactose products such as cheese and ice cream. A patient with lactose intolerance may experience bloating, gas and flatus, and diarrhea after eating foods these foods. There is a specific breath test that can be used to diagnose this condition. Lactose intolerance can be treated fairly easily with enzyme pills (Lactaid) or milk products that have this enzyme added. Even cheese and ice cream can be found with the enzyme included. There also several non — lactose milk product alternatives, such as soy milk or rice milk. Celiac disease — also called gluten sensitivity — occurs when the body develops an abnormal response to the protein gluten which is found commonly in grains. This immune response triggers a reaction in the lining of the small intestine that can cause malabsorption. The treatment for celiac sprue is the avoidance of foods made with barley, rye, oats, or wheat. There are special breads, cookies, cakes, and cereals made without gluten. An increasing frequency with which celiac disease is diagnosed has also created awareness among restaurants so that gluten — free items are commonly found on menus. Bloating, recurrent or chronic diarrhea, anemia, weight loss, and osteoporosis are some of the signs and symptoms that develop from a gluten allergy. If you experience some of these symptoms inform your physician.

Sutha Sachar, MD (

Food allergies occur when your immune system identifies a specific food as something foreign or harmful. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE). This is what triggers histamine release that causes abdominal pain, diarrhea, nausea, or vomiting. The most common allergies include shellfish such as shrimp, lobster, and crab; peanuts; tree nuts, such as walnuts and pecans; fish; and eggs.

Albert Snow, ND (

Food allergies do not affect digestion; digestion affects food allergies. A food allergy is simply a lack of digestion. It is never the food’s fault; it only has to do with us not processing it properly. We need to stop playing the “blame game.” Our digestive system and our immune system are one and the same. It does not care or distinguish between a food and a germ. When working well it digests both. Dairy and wheat products account for most of the food allergies because they are more complex. Our body’s digestion has been “dumbed down” by the universal use of certain medications.

AA Starpoli, MD (

Gluten allergy, known as sprue of celiac disease, causes an acute inflammatory reaction at the level of the small intestine closer to the stomach proper that leads to swelling and inflammation of the proximal small intestine that prevents the proper absorption of nutrients. There is also soy allergy that causes a similar inflammatory reaction that prevents proper absorption. Lactose intolerance may be considered one as well.

William Chey, MD (

National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, defines a food allergy as “an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.” A food allergen is defined as specific components of food or ingredients within food (typically proteins) that are recognized by specific immune cells and elicit specific immune reactions resulting in characteristic symptoms. Food allergies can cause a broad range of problems ranging from mild vague symptoms like an itching sensation in the mouth or throat to severe effects on the respiratory and circulatory systems which can rarely lead to death. The most common food allergies include peanut, tree nuts, fish, shellfish, milk and egg. Though the incidence of food allergies appears to be rising, they are still rare: 4 to 8 percent of children and 1 — 4 percent of adults will have a true food allergy. Most symptoms that occur after eating food are not the result of a true food allergy. So called food intolerances refer to the development of adverse reactions to food. Food intolerances are quite common, reported by 5 to 45 percent of the general population.

Jacqueline Wolf, MD (

Food allergies are present in 3 to 4 percent of adults. Children under the age of 5 have about twice as much food allergy as adults. IgE — mediated food allergy can cause anaphylaxis (trouble breathing, throat and skin swelling, etc.) Peanuts, tree nuts, fish, and shellfish cause more anaphylactic reactions than other foods. In children milk is a common cause of food allergy also. In this condition there can be swelling of the intestinal lining and even lesions like hives in the intestine. The histamine that is released can cause nausea and/or diarrhea.

Celiac disease can be considered a non — IgE immune — mediated allergy. The reaction to the gliaden protein in gluten (a protein in wheat, barley, and rye) causes damage to the small intestine and can result in the malabsorption of nutrients, diarrhea, anemia, and even joint pain and depression. In the United States 1 in 80 to 1 in 140 people have celiac disease and the number is rising. It causes damage to the lining cells of the small intestine so that the nutrients cannot be absorbed normally and there can even be secretion of fluid into the bowel.

Diarrhea caused by food allergy

  • 1.1. Diarrhea from food allergy in twenty-six adults and four infants and children is reported. Diarrhea and other gastrointestinal symptoms due to pollen allergy and diarrhea resulting from chronic ulcerative colitis and regional enteritis due to allergy are not included.
  • 2.2. The literature containing many reports of colic and diarrhea due to food allergy in infants and children and in relatively few adults is reviewed.
  • 3.3. Because of the usual negative laboratory tests, including stool analyses for parasites and x-ray studies of the stomach, small intestine, and colon, and the failure of various drugs and diets, functional diarrhea due to psychoneurosis is a common and unfortunate diagnosis in cases due to food allergy.
  • 4.4. A personal or family history of clinical allergy may be absent. The gastrointestinal tract, especially the colon, in these patients may be the sole shock organ of allergy.
  • 5.5. Although many patients give a diet history indicating dislikes and definite or suspected disagreements and resultant symptoms from specific foods, such foods often are not responsible for the diarrhea or other associated symptoms due to allergy.
  • 6.6. Skin testing by the scratch or puncture method infrequently reveals positive reactions to any or all causative allergenic foods. Large reactions need careful consideration. The ingestion tests on the symptom-free patient may reveal allergy to none or to one or more reacting foods, as illustrated in Case 2.
  • 7.7. When a diet excluding foods causing large skin reactions or foods suspected through diet history fails to relieve the diarrhea, then our standardized fruit-free elimination diet or our minimal fruit-free elimination diet is advised.
  • 8.8. Milk, fruits, and spices have been most frequently responsible for allergic diarrhea in our patients. Allergy to many other foods, as determined by individual ingestion tests in the symptom-free patient, also occurs, as discussed in this article.
  • 9.9. This allergic diarrhea, including tenesmus and even incontinence, may be so persistent and chronic and at times associated with other symptoms of gastrointestinal allergy, headaches, allergic fatigue, and toxemia, that semi- and even complete invalidism may result for months or even years.

What is a food intolerance?

There can be many causes of food intolerance, and we will take a look at each of these in turn.

1) Absence of an enzyme

Enzymes are needed to digest foods fully. If some of these enzymes are missing, or insufficient, proper digestion may be undermined.

People who are lactose intolerant do not have enough lactase, an enzyme that breaks down milk sugar (lactose) into smaller molecules that the body can break down further and absorb through the intestine. If lactose remains in the digestive tract, it can cause spasm, stomachache, bloating, diarrhea, and gas.

People with an allergy to milk protein have similar symptoms to those with lactose intolerance; that is why lactose intolerant individuals are commonly misdiagnosed as allergic.

Researchers from Mary Bridge Children’s Hospital and Health Center in Tacoma, WA, found that fructose intolerance is common in children with recurrent or functional abdominal pain.

Nearly all foods require an enzyme for proper digestion. According to the British Allergy Foundation, enzyme deficiencies are a common cause of food intolerance.

2) Chemical causes of food intolerance

Certain chemicals in foods and drinks can cause intolerance, including amines in some cheeses, and caffeine in coffee, tea, and chocolates. Some people are more susceptible to these chemicals than others.

3) Food poisoning – toxins

Some foods have naturally-occurring chemicals that can have a toxic effect on humans, causing diarrhea, nausea, and vomiting.

Undercooked beans have aflatoxins that can cause extremely unpleasant digestive problems. Fully cooked beans do not have the toxin. Hence, people may wonder why they react to beans after one meal, and not after another.

4) Natural occurrence of histamine in some foods

Some foods, such as fish that has not been stored properly, can have an accumulation of histamine as they “rot.” A number of people are particularly sensitive to this naturally-occurring histamine and develop skin rashes, abdominal cramps, diarrhea, vomiting, and nausea.

Often, the symptoms are similar to anaphylaxis (a strong allergic reaction).

5) Salicylates are present in many foods

Salicylate intolerance, also known as salicylate sensitivity, occurs when somebody reacts to normal amounts of ingested salicylate.

Salicylates are derivatives of salicylic acid, which occurs naturally in plants as a defense mechanism against harmful bacteria, fungi, insects, and diseases.

The chemicals are found in many foods and most people can consume salicylate-containing foods without any adverse effects. However, some people suffer symptoms after eating large amounts. Salicylate intolerant individuals should avoid foods that contain high levels.

Salicylates are present in most plant-sourced foods, including the majority of fruits and vegetables, spices, herbs, tea, and flavor additives. Mint-flavoring, tomato sauce, berries, and citrus fruits have particularly high levels.

Processed foods with flavor additives are usually high in salicylates as well.

Why the world is becoming more allergic to food

Image copyright Getty Images

Around the world, children are far more likely than ever before to develop food allergies.

Inquiries into the deaths of British teenagers after eating buttermilk, sesame and peanut have highlighted the sometimes tragic consequences. Last year, a six-year-old girl in Western Australia died as the result of a dairy allergy.

The rise in allergies in recent decades has been particularly noticeable in the West. Food allergy now affects about 7% of children in the UK and 9% of those in Australia, for example. Across Europe, 2% of adults have food allergies.

Life-threatening reactions can be prompted even by traces of the trigger foods, meaning patients and families live with fear and anxiety. The dietary restrictions which follow can become a burden to social and family lives.

While we can’t say for sure why allergy rates are increasing, researchers around the world are working hard to find ways to combat this phenomenon.

Image copyright PA Media Image caption Owen Carey was celebrating his 18th birthday when he died after eating buttermilk

What causes an allergy?

An allergy is caused by the immune system fighting substances in the environment that it should see as harmless, known as allergens.

These innocent substances become targets, leading to allergic reactions.

Symptoms range from skin redness, hives and swelling to – in the most severe cases – vomiting, diarrhoea, difficulty breathing and anaphylactic shock.

Some of the most common foods for children to be allergic to are:

  • milk
  • eggs
  • peanuts
  • tree nuts (eg walnuts, almonds, pine nuts, brazil nuts, pecans)
  • sesame
  • fish
  • shellfish (eg crustaceans and molluscs)

Where are food allergies most likely to occur?

The frequency of food allergy has increased over the past 30 years, particularly in industrialised societies. Exactly how great the increase is depends on the food and where the patient lives.

For example, there was a five-fold increase in peanut allergies in the UK between 1995 and 2016.

A study of 1,300 three-year-olds for the EAT Study at King’s College London, suggested that 2.5% now have peanut allergies.

Australia has the highest rate of confirmed food allergy. One study found 9% of Australian one-year-olds had an egg allergy, while 3% were allergic to peanuts.

Image copyright Getty Images

The increase in allergies is not simply the effect of society becoming more aware of them and better at diagnosing them.

It is thought that allergies and increased sensitivity to foods are probably environmental, and related to Western lifestyles.

We know there are lower rates of allergies in developing countries. They are also more likely to occur in urban rather than rural areas.

Factors may include pollution, dietary changes and less exposure to microbes, which change how our immune systems respond.

Migrants appear to show a higher prevalence of asthma and food allergy in their adopted country compared to their country of origin, further illustrating the importance of environmental factors.

Image copyright Getty Images

Some possible explanations

There is no single explanation for why the world is becoming more allergic to food, but science has some theories.

One is that improved hygiene is to blame, as children are not getting as many infections.

Parasitic infections, in particular, are normally fought by the same mechanisms involved in tackling allergies. With fewer parasites to fight, the immune system turns against things that should be harmless.

Another idea is that vitamin D can help our immune system develop a healthy response, making us less susceptible to allergies. Most populations around the world do not get enough vitamin D for several reasons, including spending less time in the sun. In the US, the rate of vitamin D deficiency is thought to have almost doubled in just over a decade.

A newer, “dual allergen exposure” theory, suggests food allergy development is down to the balance between the timing, dose and form of exposure.

For example, the development of the allergy antibodies can take place through the skin, particularly through inflamed skin in babies with eczema.

But it is thought that eating trigger foods during weaning can lead to a healthy response and prevent the allergy developing, because the gut’s immune system is prepared to tolerate bacteria and foreign substances, such as food.

This was the basis for King’s College London’s LEAP Study, which showed about an 80% reduction in peanut allergy in five-year-old children who regularly ate peanut from the year they were born.

This study led to changes in US guidelines about peanut consumption in infancy. UK parents have been advised to consult their GP first.

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Human impact

The deaths of UK teenagers suffering from food allergies highlights the human impact of this condition, and the importance of clear and accurate labelling.

There is currently no cure for food allergy, and managing the condition relies on avoiding the offending foods and on an emergency treatment plan in case of exposure.

But even making an initial diagnosis is challenging. The main way to identify food allergies is for a patient to gradually eat increased amounts of that food under medical supervision.

However, this is distressing for children, and has the risk of causing an allergic reaction. The accompanying tests of their immune systems’ reaction can also give a false positive in non-allergic children.

Image copyright Family handout/PA Wire Image caption British teenager Natasha Ednan-Laperouse died after eating a baguette containing sesame seeds

At King’s College London we have developed an alternative; a blood test which has proved accurate in diagnosing peanut allergy compared with existing methods.

These tests now cover the foods responsible for 90% of children’s allergies, and will hopefully be available to patients in the next couple of years.

Even following a successful diagnosis, avoiding trigger foods is difficult and accidental reactions are common.

Allergen immunotherapy – administering small amounts of the substance – has been shown to reduce the sensitivity of allergic patients and can protect against accidental exposure.

A recent immunotherapy drug trial found 67% of peanut-allergic subjects could consume the equivalent of two peanut kernels after a year, compared to 4% of the control group. Nevertheless, they are still allergic.

Other treatments are being investigated for food allergy, and are much needed.

In the meantime, allergies will remain a source of worry and part of daily life for the children and their parents.

About this piece

This analysis piece was commissioned by the BBC from an expert working for an outside organisation.

Dr Alexandra Santos is a Senior Clinical Lecturer at the Department of Paediatric Allergy, King’s College London.

This piece was first published in December 2018.

Edited by Eleanor Lawrie

Living With Food Allergies

If your child has symptoms after eating certain foods, he or she may have a food allergy.

A food allergy occurs when the body’s immune system sees a certain food as harmful and reacts by causing symptoms. This is an allergic reaction. Foods that cause allergic reactions are allergens.

Two Categories of Food Allergies

  1. Immunoglobulin E (IgE) mediated. Symptoms result from the body’s immune system making antibodies called Immunoglobulin E (IgE) antibodies. These IgE antibodies react with a certain food.
  2. Non-IgE mediated. Other parts of the body’s immune system react to a certain food. This reaction causes symptoms, but does not involve an IgE antibody. Someone can have both IgE mediated and non-IgE mediated food allergies.

IgE Mediated Food Allergies

The IgE mediated food allergies most common in infants and children are eggs, milk, peanuts, tree nuts, soy and wheat. The allergic reaction can involve the skin, mouth, eyes, lungs, heart, gut and brain. Some of the symptoms can include:

  • Skin rash, itching, hives
  • Swelling of the lips, tongue or throat
  • Shortness of breath, trouble breathing, wheezing
  • Stomach pain, vomiting, diarrhea
  • Feeling like something awful is about to happen

Sometimes allergy symptoms are mild. Other times they can be severe. Take all allergic symptoms seriously. Mild and severe symptoms can lead to a serious allergic reaction called anaphylaxis (anna-fih-LACK-sis). This reaction usually involves more than one part of the body and can get worse fast. Anaphylaxis must be treated right away to provide the best chance for improvement and prevent serious, potentially life-threatening complications.

Treat anaphylaxis with epinephrine. This medicine is safe and comes in an easy-to-use device called an auto-injector. You can’t rely on antihistamines to treat anaphylaxis. The symptoms of an anaphylactic reaction occur shortly after contact with an allergen. In some individuals, there may be a delay of two to three hours before symptoms first appear.

Cross-Reactivity and Oral Allergy Syndrome

Having an IgE mediated allergy to one food can mean your child is allergic to similar foods. For example, if your child is allergic to shrimp, he or she may be allergic to other types of shellfish, such as crab or crayfish. Or if your child is allergic to cow’s milk, he or she may also be allergic to goat’s and sheep’s milk. The reaction between different foods is called cross-reactivity. This happens when proteins in one food are similar to the proteins in another food.

Cross-reactivity also can occur between latex and certain foods. For example, a child who has an allergy to latex may also have an allergy to bananas, avocados, kiwis or chestnuts.

Some people who have allergies to pollens, such as ragweed and grasses, may also be allergic to some foods. Proteins in the pollens are like the proteins in some fruits and vegetables. So, if your child is allergic to ragweed, he or she may have an allergic reaction to melons and bananas. That’s because the protein in ragweed looks like the proteins in melons and bananas. This condition is oral allergy syndrome.

Symptoms of an oral allergy syndrome include an itchy mouth, throat or tongue. Symptoms can be more severe and may include hives, shortness of breath and vomiting. Reactions usually occur only when someone eats raw food. In rare cases, reactions can be life-threatening and need epinephrine.

Non-IgE Mediated Food Allergies

Most symptoms of non-IgE mediated food allergies involve the digestive tract. Symptoms may be vomiting and diarrhea. The symptoms can take longer to develop and may last longer than IgE mediated allergy symptoms. Sometimes, a reaction to a food allergen occurs up 3 days after eating the food allergen.

When an allergic reaction occurs with this type of allergy, epinephrine is usually not needed. In general, the best way to treat these allergies is to stay away from the food that causes the reaction. Below are examples of conditions related to non-IgE mediated food allergies.

Not all children who react to a certain food have an allergy. They may have food intolerance. Examples are lactose intolerance, gluten intolerance, sulfite sensitivity or dye sensitivity. Staying away from these foods is the best way to avoid a reaction. Your child’s doctor may suggest other steps to prevent a reaction. If your child has any food allergy symptoms, see your child’s doctor or allergist. Only a doctor can properly diagnose whether your child has an IgE- or non-IgE food allergy. Both can be present in some children.

Eosinophilic Esophagitis (EoE)

Eosinophilic (ee-uh-sin-uh-fil-ik) esophagitis is an inflamed esophagus. The esophagus is a tube from the throat to the stomach. An allergy to a food can cause this condition.

With EoE, swallowing food can be hard and painful. Symptoms in infants and toddlers are irritability, problems with eating and poor weight gain. Older children may have reflux, vomiting, stomach pain, chest pain and a feeling like food is “stuck” in their throat. The symptoms can occur days or even weeks after eating a food allergen.

EoE is treated by special diets that remove the foods that are causing the condition. Medication may also be used to reduce inflammation.

Food Protein-Induced Enterocolitis Syndrome (FPIES)

FPIES is another type of food allergy. It most often affects young infants. Symptoms usually don’t appear for two or more hours. Symptoms include vomiting, which starts about 2 hours or later after eating the food causing the condition. This condition can also cause diarrhea and failure to gain weight or height. Once the infant stops eating the food causing the allergy, the symptoms go away. Rarely, severe vomiting and diarrhea can occur which can lead to dehydration and even shock. Shock occurs when the body is not getting enough blood flow. Emergency treatment for severe symptoms must occur right away at a hospital. The foods most likely to cause a reaction are dairy, soy, rice, oat, barley, green beans, peas, sweet potatoes, squash and poultry.

Allergic Proctocolitis

Allergic proctocolitis is an allergy to formula or breast milk. This condition inflames the lower part of the intestine. It affects infants in their first year of life and usually ends by age 1 year.

The symptoms include blood-streaked, watery and mucus-filled stools. Infants may also develop green stools, diarrhea, vomiting, anemia (low blood count) and fussiness. When properly diagnosed, symptoms resolve once the offending food(s) are removed from the diet.

Medical review December 2014.

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