Sense of smell facts

There’s no mistaking the odor of burning rubber for the fresh smell after a summer rain, but now new research shows the human nose can distinguish among many more odors than once thought.

People often say that humans can distinguish among only 10,000 different odors. But in fact, the nose can tell apart at least 1 trillion different odors, and possibly many more, the new findings suggest.

“We debunk this old, made-up number of 10,000,” said Leslie Vosshall, an olfaction researcher at the Rockefeller University in New York and a co-author of the study detailed today (March 20) in the journal Science. “It gave humans an inferiority complex about our sense of smell,” she said, referring to the keen sense of smell in other animals.

Animals use their senses of smell to find food, avoid danger and even find mates.

“We’re much better smellers than we thought we were,”Vosshall told Live Science.

The number 10,000 has appeared in scientific literature and popular magazines, but only a few researchers have actually tested it. In the new study, the researchers say they suspected the human nose could smell many more than 10,000 scents, based on the fact that a typical nose has 400 olfactory receptors. The human eye has only three color receptors, and yet people can see up to 10 million colors, the researchers noted.

Testing whether people could smell 10,000 different scents or more would be an impossible task. So Vosshall and colleagues tested a subset of these odors in different combinations, and extrapolated their results to estimate the total number of scents the human nose can distinguish.

The researchers created mixtures of 128 different scent molecules. Individually, the molecules resembled odors such as grass or citrus, but when they were all combined, the mix smelled unfamiliar.

Vosshall’s team gave the volunteers three vials of scents — two of one scent along with a third, different scent — and told them to identify the unique odor. The volunteers repeated the process for more than 260 sets of vials.

The researchers counted how often the volunteers correctly identified the different vial, and extrapolated this to estimate how many scents an average person could distinguish out of all possible mixtures of 128 molecules.

The findings revealed that humans can smell at least 1 trillion different scents. But the actual number may be much higher, because there are more than 128 odor molecules, Vosshall said.

The researchers didn’t break the results down by gender, ethnicity or other factors for this study. But their previous research suggests that young, Caucasian women who are non-smokers and of normal weight are the best smellers.

Vosshall hopes the research will inspire people to smell the world in a new way. “Don’t constrain yourself to 10,000 scents — use the full trillion,” she said.

Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

The human sense of smell: It’s stronger than we think

But guess what? It’s a big myth. One that has survived for the last 150 years with no scientific proof, according to Rutgers University-New Brunswick neuroscientist John McGann, associate professor in the Department of Psychology, School of Arts and Sciences, in a paper published on May 12 in Science.

McGann, who has been studying the olfactory system, or sense of smell, for the past 14 years, spent part of the last year reviewing existing research, examining data and delving into the historical writings that helped create the long-held misconception that human sense of smell was inferior because of the size of the olfactory bulb.

“For so long people failed to stop and question this claim, even people who study the sense of smell for a living,” says McGann, who studies how the brain understands sensory stimuli using information gleaned from prior experience.

“The fact is the sense of smell is just as good in humans as in other mammals, like rodents and dogs.” Humans can discriminate maybe one trillion different odors, he says, which is far more, than the claim by “folk wisdom and poorly sourced introductory psychology textbooks,” that insist humans could only detect about 10,000 different odors.

McGann points to Paul Broca, a 19th century brain surgeon and anthropologist as the culprit for the falsehood that humans have an impoverished olfactory system — an assertion that, McGann says, even influenced Sigmund Freud to insist that this deficiency made humans susceptible to mental illness.


“It has been a long cultural belief that in order to be a reasonable or rational person you could not be dominated by a sense of smell,” says McGann. “Smell was linked to earthly animalistic tendencies.” The truth about smell, McGann says, is that the human olfactory bulb, which sends signals to other areas of a very powerful human brain to help identify scents, is quite large and similar in the number of neurons to other mammals.

The olfactory receptor neurons in the nose work by making physical contact with the molecules composing the odor, and they send this information back to that region of the brain.

“We can detect and discriminate an extraordinary range of odors; we are more sensitive than rodents and dogs for some odors; we are capable of tracking odor trails; and our behavioral and affective states are influenced by our sense of smell,” McGann writes in Science.

In Broco’s 1879 writings, he claimed that the smaller volume of the olfactory area compared to the rest of the brain meant that humans had free will and didn’t have to rely on smell to survive and stay alive like dogs and other mammals.

In reality, McGann says, there is no support for the notion that a larger olfactory bulb increases sense of smell based solely on size and insists that the human sense of smell is just as good and that of animals.


“Dogs may be better than humans at discriminating the urines on a fire hydrant and humans may be better than dogs at discriminating the odors of fine wine, but few such comparisons have actual experimental support,” McGann writes in Science.

The idea that humans don’t have the same sense of smell abilities as animals flourished over the years based on some genetic studies which discovered that rats and mice have genes for about 1000 different kinds of receptors that are activated by odors, compared to humans, who only have about 400.

“I think it has been too easy to get caught up in numbers,” says McGann. “We’ve created a confirmation bias by working off a held belief that humans have a poor sense of smell because of these lower numbers of receptors, which in reality is still an awful lot.”

The problem with this continuing myth, McGann says, is that smell is much more important than we think. It strongly influences human behavior, elicits memories and emotions, and shapes perceptions.

Our sense of smell plays a major, sometimes unconscious, role in how we perceive and interact with others, select a mate, and helps us decide what we like to eat. And when it comes to handling traumatic experiences, smell can be a trigger in activating PTSD.

While smell can begin to deteriorate as part of the aging process, McGann says, physicians should be more concerned when a patient begins to lose the ability to detect odors and not just retreat back to the misconception that humans’ sense of smell is inferior.

“Some research suggests that losing the sense of smell may be the start of memory problems and diseases like Alzheimer’s and Parkinson’s,” says McGann. “One hope is that the medical world will begin to understand the importance of smell and that losing it is a big deal.”

The Limits of the Human Nose

The air contains an incalculable number of volatile compounds, which can be detected only by one sense: the smell.

There are about 110,000 smells in nature.

The human being perceives only about 100-200.

But not everybody detects them in the same way. The olfaction of children is much finer. While those working in the perfume industry can detect 600-800 smells!

In women, the sense of olfaction is strongest around the ovulation period, significantly stronger than during other parts of the menstrual cycle and also stronger than the sense in males.

The left nostril catches smells better than the right one.

The man is an audiovisual animal, with a rudimentary olfaction, but some animals can even communicate using olfaction through some chemicals called pheromones.

Birds, too, have poor olfaction, except kiwi, condors and their relatives (black and turkey vultures), and albatrosses with their relatives (petrels and shearwaters).

Amongst mammals, cetaceans (whales, dolphins) present anosmia and monkeys present a weak olfaction.

Insects, especially the colonial ones (ant, termites, bees), keep a real olfactory conversations using pheromones.

In people, pheromone communication is almost inexistent. People secret pheromones, but in extremely small doses and their psychological effects are hard to detect.

In humans, the olfactory surface is about 10 square centimeters (in dogs 150!), compassing about 1 million olfactive cells. In dogs and other mammals, the olfactive mucosa is extemely folded and much more densely innervated.

For an olfactive signal to emerge, it is necessary that 8 molecules of a specific substance reach an olfactive cell. And for the olfactive sensation to appear, at least 40 olfactive cells must be stimulated.

For 80 % of the people, the nose is not exactly on the middle of the face, but to the right. This will help people detect the source of a smell, as the slight difference permits a comparison. (the same happens with the owls, which have their ears disposed asymmetrically to locate the source of a noise in the dark). 70 % of infections are propagated through the nose.

Try to smell a handful of salt. If it’s pure, you won’t sense anything. For people, quinine is inodorous. But a dog will feel them even dissolved at 1:10,000 (a gram in a cub of water). However, we will detect them better in food.

When we have a cold, we do not feel the taste of the aliments. But the cold affects the nose, not the taste receptors. But we associate the taste of the aliments with their smell. If you try to taste open binded and nose tapped butter or grease, tea or water, they will seem impossible to identify, appearing tasteless.

Our nose is the location of an amazing sense that the modern humans lost it because they don’t use it anymore. But indigenous populations and animals do have it and use it. It’s the biological compass, made of many magnetite (an iron oxide) crystals, located at the base of the nose’s sinus. This organ enables the organism to detect the north.

That’s why – unlike the explorers – the people of the jungle tribes never get lost in the forest. The first Europeans in contact with these tribes thought they had a keen sense of the details but the same thing happened with the nomad African tribes from the deserts, where marks change quickly.

10 Incredible Facts About Your Sense of Smell

Olfaction, the sense of smell, might be the Rodney Dangerfield of the five senses: It gets no respect — or at least not as much as it should. From how many different scents the nose can pick up to the link between smell and overall health, there are a lot of things about this sense that may surprise you.

Here are 10 strange but true facts about our sense of smell:

1. People can detect at least one trillion distinct scents. Scientists thought that the human nose could only detect about 10,000 different smells, but that information was based on a study from 1927 and very outdated. This year, researchers from Rockefeller University tested people’s sense of smell by using different mixtures of odor molecules. The results, published in the journal Science, showed that the nose can smell at least one trillion distinct scents.

So how exactly does humans’ sense of smell work? When odors enter the nose, they travel to the top of the nasal cavity to the olfactory cleft where the nerves for smell are located, explains Amber Luong, MD, PhD, assistant professor at the University of Texas Health Science Center at Houston. “There, the odorant is detected by various receptors located on the nerve cells and the combination of activated nerves travel to the brain. The combination of activated nerves generates all the unique smells that we as humans can detect,” says Dr. Luong.

Some of the most pleasant or pleasurable scents include vanilla, some forms of orange scents, cinnamon, crayons, and cookies, according to Luong and Dolores Malaspina, MD, MSPH, professor of clinical psychiatry at Columbia University in New York.

2. Scent cells are renewed every 30 to 60 days. The sense of smell is the only cranial nerve — nerves that emerge from the brain and control bodily functions including eye movement, hearing, taste, and vision — that can regenerate, says Luong.

3. You can smell fear and disgust. You can smell feelings of fear and disgust through sweat, and then you can experience the same emotions, according to a 2012 study published in the journal Psychological Science.

Researchers collected sweat from men as they watched movies that caused these feelings. To remain odor-neutral for the sweat test, the men used scent-free products, and quit smoking and using alcohol. Women participants then completed visual search tests, while unknowingly smelling the sweaty samples. The women’s eye movements and facial expressions were recorded during this time.

The researchers found that women who smelled the “fear sweat” opened their eyes widely in a fearful expression, and women who smelled the “disgust sweat” also displayed facial expressions of disgust.

4. Smell is the oldest sense. Chemodetection — detecting chemicals related to smell or taste — is the most ancient sense, says Malaspina. “Even a single cell animal has ways to detect the chemical composition of the environment,” she adds.

5. Women have a better sense of smell than men. “Women always are better at odor and smell identification than men, and every study finds that,” says Malaspina. She says one of the reasons for this may be that women have a more developed orbital prefrontal region of the brain. It may have also evolved from an ability to discern the best possible mates, or to help women better bond with and understand newborns.

6. Age-related loss of smell is linked to race. African-Americans and Hispanics experience loss of smelling related to age earlier than Caucasians, according to a 2013 study published in the Journal of Gerontology: Medical Sciences. Researchers asked more than 3,000 adults aged 57 to 85 years to identify five common odors.

Although age-related loss of smell is common, this is the first study to examine racial differences.

Results showed non-Caucasian individuals consistently scored 47 percent lower than Caucasians, and were equivalent to being nine years older. Women from all races performed the smell test better than men, and were equivalent to being five years younger.

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The exact cause for this difference is unknown, but researchers believe genetics and environment (such as exposure to nerve-damaging substances) could be factors.

7. Dogs have nearly 44 times more scent cells than humans. “Humans have five to six million odor-detecting cells as compared to dogs that have 220 million cells,” says Luong. ”We have evolved to rely less on our sense of smell, while most animals have retained this sense.”

Another fun fact about canines and smell: Dogs can distinguish non-identical twins but not identical twins based on odors, says Malaspina.

8. Loss of smell may signal future illnesses. “Decreased sense of smell may be an early sign of Alzheimer’s or Parkinson’s disease,” says Luong. Two studies presented at the Alzheimer’s Association International Conference 2014 found that a reduced ability to identify scents was associated with brain cell function loss and advancement to Alzheimer’s disease. A study published in the Annals of Neurology also found that a diminished sense of smell can precede the development of Parkinson’s disease.

9. Each human has their own distinct odor. Like fingerprints, every person has their own distinct odor. The distinct odor you have comes from the same genes that determine tissue type, says Malaspina.

10. Decline in smell may predict death within five years. A recent study published in the journal PLOS ONE found that a decreased ability to identify scents may predict death within five years. The study looked at more than 3,000 Americans aged 57 to 85, and found that people unable to identify scents like rose, orange, and peppermint were more than three times as likely to die in the next five years.

Still, having a diminished sense of smell isn’t necessarily something to panic about. Most of the things that interfere with olfactory senses are allergies and head injuries, and not factors that suggest an increased risk of death.

“We know that new brain cells are produced throughout life in a few different olfactory areas, and the earlier death may relate to the decline of cell regeneration that is occurring in other body regions as well,” says Malaspina.

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Imagine walking into a meeting room. You shake hands with colleagues, then everyone sits down. Within seconds they all start sniffing their palms, picking up clues about you from the chemical traces left over from the handshakes.

Sniffing palms after a handshake, usually within 30 seconds of the interaction, would likely help people learn about someone’s health and genetic compatibility, according to a 2015 study by researchers in Israel. Sniffing can also offer information on people’s emotional state, such as if they are happy, sad or fearful. The smeller gleans these emotions subconsciously, of course.

For decades, scientists believed humans were not very good at detecting and identifying odors. Our animal ancestors used their noses way more than we do in modern society, says Jessica Freiherr, a neuroscientist at RWTH Aachen University, in Germany, and the author of several studies on the human sense of smell. “We are disconnected from our noses,” she says. “We need them much less in everyday life. And our vision overrides the sense of smell in a lot of situations.”

But that doesn’t mean we don’t have powerful smell potential. A 2014 study showed that we can distinguish at least 1 trillion different odors — up from previous estimates of a mere 10,000.

Awareness of our innate smelling abilities, however, is complicated because the human language doesn’t have words for a trillion smells, and much of smelling happens under the radar of our consciousness. Unlike our other senses, the olfactory nerves do not proceed directly to the brain’s thalamus, the gateway to consciousness. Instead, information feeds from the nose to cortical areas to arouse emotions and memories without our awareness. When it comes to smells, people can be influenced and not realize it.


Who Passes the Smell Test?

An animal schnoz is obviously superior to our own mediocre noses, right?

Not so fast. Matthias Laska, a biologist at Linköping University in Sweden, has been comparing senses of smell across species — including humans — for more than two decades. “The more data I collected on different species over the years, the more interesting the picture became,” Laska says.

But sizing up how sensitive the snout of, say, a seal is compared with a bat or human isn’t straightforward. People can tell you when a certain scent is no longer detectable. But each animal has to learn to associate a particular odor with a reward and then do something, like press a button, to let researchers know when they smell it.

The odors compared between species also have to be the same. That sounds obvious, but while humans have sniffed around 3,300 different scents for science — out of the trillions possible — the highest number for animals is 81, by spider monkeys. Laska only found solid enough data to compare humans with 17 species, all mammals.

Alison Mackey/Discover

However, human noses held their own. Humans tested as generally more sensitive sniffers than monkeys and rats on a limited range of odors. In fact, humans detected certain scents at lower concentrations than the notoriously top-notch nostrils of mice and pigs.

Humans even beat the indomitable dog for at least a handful of scents. These include aromas produced by plants, a logical evolutionary advantage for our ancestors seeking fruits. The majority of the odors in which dogs bested us were the fatty acids, compounds associated with their own meaty prey. “Odors that are not relevant for you, you are usually not good at ,” Laska says.

Bottom line: Humans, Laska says, “are not as hopeless as the classical wisdom will tell us, and dogs are not the super nose of the universe for everything.” — Ashley Braun

A Scented Fingerprint

If you were assaulted by a stranger you didn’t get a good look at, could you identify the person by smell in a police lineup? Would the perpetrator’s body odor be enough? It very well could be, according to a 2015 study by scientists in Portugal and Sweden.

Researchers collected body odor samples from 20 male university students. Other students then watched a video of an actual assault by a man on a woman (to stir them emotionally), while sniffing a scent they were told was that of the suspect. In reality, it was the scent of one of the 20 male students. Afterward, the sniffers were given a “lineup” of five odor samples and asked to identify the person whom they had smelled — presumably not a very enjoyable task. Results were quite impressive, though. The “witnesses” were able to pinpoint the would-be suspect 75 percent of the time.

Alison Mackey/Discover

Every person has a unique scent. “It’s like a fingerprint,” says Johan Lundström, a neuroscientist at the Karolinska Institute in Sweden. “There is a large genetic component to body odor. Even trained sniffer dogs have a hard time distinguishing between identical twins, unless the twins are on different diets.”

Scientists still don’t know how human body odor can act like a scented fingerprint. It could be from the apocrine sweat glands in the armpits, which produce odorless substances made smelly by skin bacteria. In 2015, scientists from the University of Düsseldorf identified unsaturated, or hydroxylated, branched fatty acids as the “olfactorily most dominant,” or stinkiest.

Human scent affects our brain differently than other scents. When we catch a whiff, the areas of the brain responsible for social processing light up, according to a study that used positron emission tomography (PET) to measure brain function. “There is much more information in body odor than we can extract from normal odors,” says Lundström, the study’s lead author.

Smelling Emotions

Another reason you might be able to identify a criminal, or at least someone feeling agitated, is that he or she may simply smell dangerous. In one of Freiherr’s experiments published in 2015 in the journal Chemical Senses, researchers obtained sweat from 16 men. The men took a timed math test and were falsely told they had performed below average. Disgruntled, they then participated in a workout where sweat was collected. As a control, the men took the math test again under no time constraint and were told they got an average score. Again, they followed up with a sweaty workout.

Volunteers sniffed the men’s sweat samples while taking a test that measures cognitive performance. When sniffing the sweat of the men told they scored below average, the volunteers were distracted and slower to respond during their own test. When sniffing the sweat from the men’s second workout, the volunteers scored in a manner indicating emotional neutrality.

A hefty pile of evidence suggests that emotions have a scent. What’s more, such smelled emotions may be contagious. Say you go out to meet a friend who had been watching funny videos on her mobile phone, making her feel happy. As you approach her, you catch a whiff of her scent and automatically smile. But had your friend just watched a scary movie, her body odor would have likely made you feel apprehensive.

An fMRI brain scan of a volunteer sniffing the sweat of a parachute jumper shows high activity, in yellow, in the left amygdala. Mujica-Parodi LR, Strey HH, Frederick B, Savoy R, Cox D, Botanov Y, et al. (2009) Chemosensory Cues to Conspecific Emotional Stress Activate Amygdala in Humans. PLoS ONE

Using electrodes, European researchers in 2015 measured the facial movements of volunteers who sniffed sweat samples of people who had watched either pleasant or scary videos — happy-go-lucky scenes from Disney’s The Jungle Book versus hair-raising clips from Stanley Kubrick’s The Shining. After inhaling the scent of The Jungle Book watchers, participants “assumed a genuine happy facial expression,” says Jasper de Groot, a psychologist from Utrecht University in the Netherlands. “It was subtle, yet significant.”

Meanwhile, smelling the body odor of stressed-out people ups our vigilance, while the odor of people who had just watched something disgusting makes our faces twist in disgust. In fMRI scans, people sniffing the sweat from first-time parachute jumpers lit up the brain’s left amygdala, where basic emotions are processed, suggesting fear is contagious, too.

“These chemosignals ring an alarm bell in your brain to attract your attention,” Freiherr says. “Maybe you can smell a dangerous place because somebody was there five minutes ago feeling scared.”

Scent of a Lover

Inhaling body odor can offer more information about people than their emotional state. The health and biological compatibility of the opposite sex might also be gleaned, all the better to help pick the perfect mate.

In an experiment published in 2014 in the journal Psychological Science, people could tell who showed signs of sickness by their body odor (the researchers injected the sweat donors with a toxin that prompted an immune reaction). From an evolutionary standpoint, smelling sickness or disease has advantages. Choosing an unhealthy partner is not the best way to pass on your genes.

Yet of maybe even greater gene-spreading significance is the ability to tell differences in MHC — the major histocompatibility complex, a gene family linked to the immune system and body scent. Scientists have long known that animals such as mice and rats can tell how genetically related they are to others of their species by smelling one another’s urine. Studies show humans are masters of this skill, too — and thankfully, no urine smelling is necessary. When scientists from the University of Chicago asked a group of women to sniff T-shirts worn for two consecutive nights by different men, the women pinpointed their closest genetic matches — even though there could be millions of unique combinations of MHC genotypes.

Dean Drobot/

A study by researchers from McGill University in Canada involving neuroimaging, which creates pictures of the brain’s structure and neural activity, showed that smelling the body odor of someone closely related activates the dorsomedial prefrontal cortex, a part of the brain responsible for recognizing family.

“Biologically, it makes sense. We want to protect our own gene pool,” Lundström says. But “it’s not so much picking the best partner, it’s deselecting bad partners.” Research shows that people — and women in particular — prefer potential partners who are somewhat genetically related, but not too related. Having children with someone with an MHC genotype that is too similar, studies show, can lead to spontaneous abortion or low birth weight. Conversely, pursuing someone with a close (or semi-close) genetic makeup means preserving adaptations to an environment — think regional people having immunity to local strains of pathogens.

Meanwhile, some scents can make us appear more attractive to potential partners. Take the aroma of grapefruit. In a study that involved guessing the age of women shown in photos, participants knocked off 12 years from actual ages if they smelled, and enjoyed the smell of, grapefruit. If the participants smelled spicy and floral notes, the women appeared four pounds slimmer.

And it’s much safer to buy cologne for people within your family rather than outside it. Genetic kinship seems to influence smell preference. In one study, people with similar genotypes chose similar perfume ingredients.

That New-Baby Smell

If you’ve ever thought there is something special about the smell of babies, you’re right. In 2013, scientists from Germany, Canada and Sweden took fMRI scans of 30 women while they sniffed the cotton undershirts of newborns. The new moms’ thalamus lit up more than that of women without kids, suggesting the mothers’ increased attention. All the women showed activity in the brain’s neostriate areas, where the reward system lies.

The fresh scent of newborns activates the same biological mechanism in women as a baby’s “very round eyes, the round face, the cute voice,” says Lundström, who was involved in the study. It is nature’s way of bonding mother and child. Although only women were tested in that particular study, Lundström suspects that similar results would be found in men.

For now, researchers haven’t managed to pinpoint the molecules responsible for that new-baby smell. Lundström and his colleagues have some chemicals under the microscope (figuratively and literally), and are even researching whether the newborn smell could be used to treat depression. The team is also investigating whether women who suffer postpartum depression lack receptors for newborn scent molecules or don’t receive the reward signals from the baby smell.

Similar to our ability to winnow out incompatible mates by scent, new moms can distinguish their biological babies by sniffing them. In one classic study, mothers identified the smell of their child from two other newborns six hours after birth, even though mother and child were separated for most of that time. Sixty-one percent of mothers guessed right. (Chance would be 33 percent.)

Sickova Tatyana/

This works the other way, too. Newborns know the scent of Mom by the second day of life. In a 2015 study, breast-fed babies turned their heads toward scent pads of their mothers for nearly twice as long as the pads of lactating strangers. “Mother’s body odor might be learned to some degree, as this odor is related to the chemosensory signature of the amniotic fluid, which the unborn senses,” says Katrin T. Lübke, an olfaction researcher at the University of Düsseldorf in Germany who was not part of the study.

Yet simple exposure is not enough for parents to identify the smell of their nonbiological children. In one study, mothers were able to pick the scents of their biological kids in 90 percent of cases, but with stepchildren, they were only 28 percent accurate. Among families in Wales interviewed for a government-funded study on failed adoptions, several parents mentioned that the distinctive body odor of their child had a negative impact on the relationship. One mom said her adopted daughter “didn’t smell right.”

Although our noses can sometimes lead us astray, in general they send us important messages about other people. Be careful, a dangerous person was here and may be lurking nearby. Be cautious, a person is sick and may be contagious. Be alert, your newborn needs your care. Be flirtatious, this person is a potential partner. Being more open to our sense of smell has payoffs, even in modern times.

“Listen to your inner voice, because your inner voice might be your nose telling you what to do,” Lundström says.

Here are 25 Interesting Facts About Smells and Odors.

1-5 Interesting Facts About Smells and Odors

1. Body Odor might actually help us find our best-fit romantic partners. Body odor is largely influenced by Major Histocompatibility Complex (MHC) molecules, which are genetically determined and linked to the immune system. Experiments on non-human animals and human participants have shown that we tend to judge potential sexual partners as more attractive if their MHC composition is substantially different from our own. In other words, opposites really might attract, perhaps because such variation in our immunity makes the population more resistant to disease. – Source

2. Meat from a non-castrated pig will have an unpleasant odor when cooked, referred to as “Boar Taint.” While the odor creates no safety issue, nearly 50% of us, especially women, are sensitive to these unpleasant smells. Traditionally, farmers have managed off odors by surgically castrating male pigs. This practice is used around the world with 95% of the male pig population. – Source

3. Putting some dry tea bags in smelly running shoes or a smelly bag when not in use will absorb the musky scents while imparting some of their own more pleasant aroma. – Source

4. Before the rain begins, one of the first odors you may notice as winds pick up and clouds roll in is a sweet, pungent zing in your nostrils. That’s the sharp, fresh aroma of ozone. The scent of ozone heralds stormy weather because a thunderstorm’s downdrafts carry ozone from higher altitudes to nose level. – Source

5. The Macrocilix maia moth is a mimic insect that confuses its predators with its wing patterns, which paints an entire scene. It looks like a watercolor. Two red-eyed muscomorph flies feed from fresh bird droppings, complete with light glinting off their wings. It even releases a pungent odor to drive home the deception. – Source

6-10 Interesting Facts About Smells and Odors

6. Most people produce the odorous compounds after eating asparagus, but only about 22% of the population has the autosomal genes required to smell them. – Source

7. East Asians (Chinese, Koreans, and Japanese) have fewer apocrine sweat glands compared to people of other descent, and the lack of these glands make East Asians less prone to body odor. – Source

8. People with psychopathic tendencies have an impaired sense of smell, which points to inefficient processing in the front part of the brain. Those scoring highly on psychopathic traits were more likely to struggle to both identify smells and tell the difference between smells, even though they knew they were smelling something. – Source

9. The lovely scent of cut grass is the reek of plant anguish. When attacked, plants release airborne chemical compounds. Plants can use these compounds almost like language, notifying nearby creatures who can “rescue” them from insect attacks. – Source

10. Dogs have bacteria on their paws that make them smell like corn chips. This phenomenon is commonly referred to as “Frito Feet.” – Source

11-15 Interesting Facts About Smells and Odors

11. An elephant’s ability to smell water is so refined tjat they can sometimes detect water sources from as much as 12 miles away. – Source

12. When the bubonic plague struck London in 1665, one of the “cures” the plague doctors prescribed was fart jar. To combat the plague people would literally pass gas into a jar, then take a whiff. – Source

13. Farts smell worse in the shower because the high turbidity of the air in the shower circulates the gas through the space effectively. Secondly, the high humidity and high temperature condition in the shower enhances a person’s sense of smell and taste. The farts don’t actually smell worse, it’s just that we can smell them better than usual. – Source

14. Maned wolf pee smells like cannabis, so much so that police were once called to the Rotterdam Zoo in the Netherlands to search out a pot smoker, only to find that whoever made the report had been fooled by the scent of maned wolf urine. – Source

15. Old people smell is actually caused by a chemical compound called 2-nonenal. Created by the oxidative breakdown of other chemicals over time, it produces what’s described as an “unpleasant greasy and grassy odor” in people and is also responsible for some of the “cardboard” flavor of stale beer. People’s concentration of 2-nonenal increases with age and old people secrete three times as much as a middle-aged person.- Source

16-20 Interesting Facts About Smells and Odors

16. The smell of Parmesan cheese and vomit are actually not that different and when blindfolded, people often can’t tell the difference between the smell of Parmesan cheese and vomit. – Source

17. Human poop and farts get their foul smell from the chemical compounds Skatole and Indole (among others). At low concentrations, these compounds smell flowery, and are used in perfumes. USA and Israel have used Skatole in crowd control sprays. The stench does not wash off skin for 3 days. – Source

18. Your nostrils split their workload. Throughout the day, they each take breaks in a process of alternating congestion and decongestion called the nasal cycle. At a given moment, if you’re breathing through your nose, the lion’s share of the air is going in and out of one nostril, with a much smaller amount passing through the other to enhance your sense of smell. – Source

19. Bunchosia argentea, commonly known as Peanut Butter Tree is a tropical tree native to Venezuela and Colombia in South America. It produces a small red-orange fruits with sticky, dense pulp and a flavor resembling that of dried figs or peanut butter, hence the name. Additionally, the scent is unmistakably of peanut butter. – Source

20. Paleontological research has shown that the part of the human brain that controls hearing and our sense of smell shrank around the same time as humans began to domesticate dogs. – Source

21-25 Interesting Facts About Smells and Odors

21. Coffee doesn’t taste like it smells because 300 of the 631 chemicals that combine to form its complex aroma are wiped out by saliva, causing the flavor to change before we swallow it.– Source

22. The molecules which produce the smell of lemons and oranges are mirror images, but our noses are sensitive enough to know the difference. – Source

23. Bee’s discreet sense of smell, equivalent to a dog’s, is being exploited as a much cheaper way to detect various odors in the environment. There is a device called the Vasor 136 containing 36 cartridges each containing one bee. Each bee is trained to a different smell. Light sensors detect when their tongues stick out determining which smell is present. – Source

24. In 1987, Baltimore Gas and Electric Company sent out scratch and sniff stickers to educate the public on the smell of a gas leak, only for it to backfire when the smell of the unopened envelopes were mistaken for gas leaks. – Source

25. British intelligence services experimented with using semen as an invisible ink to write top-secret letters. First chief of the SIS Mansfield c*mming said that the best invisible ink is semen , which did not react to the main methods of detection. Furthermore it had the advantage of being readily available. In addition, at least one agent had to be reminded to use only fresh supplies of the ‘ink’ when correspondents began noticing an unusual smell. – Source

26-30 Interesting Facts About Smells and Odors

26. Several astronauts who have gone on spacewalks have said that upon stepping back into the space station and removing their helmets, they get a strong, distinctive whiff of the space. The odor clings to their suit, helmet, gloves and tools. The clinging particles have the acrid aroma of seared steak, hot metal and welding fumes. – Source

27. A supplement that increases milk production called Fenugreek, has a side effect that may cause your baby to smell like maple syrup. – Source

28. The “metallic” smell left on your hands after handling coins isn’t the smell of the coin. It’s the smell of our own skin. The musty odor comes from chemical compounds in our own skin, which are transformed in an instant by the touch of iron or copper. – Source

29. Seizure detection dogs are new type of service dogs has only been on the scene for about 10 years or so now, but have made quite an impact on those suffering from certain seizure disorders. These highly skilled dogs smell seizures 30 minutes before they happen and warn their owners. – Source

30. There is a hostage negotiation strategy called “Bringing Home the Bacon” where negotiators fry bacon outside of the hostage area, making the hostage taker hungry from the smell and more willing to negotiate. – Source

Smell Disorders

How common are smell disorders?

Your sense of smell helps you enjoy life. You may delight in the aromas of your favorite foods or the fragrance of flowers. Your sense of smell is also a warning system, alerting you to danger signals such as a gas leak, spoiled food, or a fire. Any loss in your sense of smell can have a negative effect on your quality of life. It can also be a sign of more serious health problems.

One to two percent of North Americans report problems with their sense of smell. Problems with the sense of smell increase as people get older, and they are more common in men than women. In one study, nearly one-quarter of men ages 60–69 had a smell disorder, while about 11 percent of women in that age range reported a problem.

Many people who have smell disorders also notice problems with their sense of taste. To learn more about your sense of taste, and how it relates to your sense of smell, read the NIDCD’s Taste Disorders publication.

How does your sense of smell work?

Your sense of smell—like your sense of taste—is part of your chemosensory system, or the chemical senses.

Your ability to smell comes from specialized sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside the nose. These cells connect directly to the brain. Each olfactory neuron has one odor receptor. Microscopic molecules released by substances around us—whether it’s coffee brewing or pine trees in a forest—stimulate these receptors. Once the neurons detect the molecules, they send messages to your brain, which identifies the smell. There are more smells in the environment than there are receptors, and any given molecule may stimulate a combination of receptors, creating a unique representation in the brain. These representations are registered by the brain as a particular smell.

Smells reach the olfactory sensory neurons through two pathways. The first pathway is through your nostrils. The second pathway is through a channel that connects the roof of the throat to the nose. Chewing food releases aromas that access the olfactory sensory neurons through the second channel. If the channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells. As a result, you lose much of your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.

Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. Without smell, foods tend to taste bland and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.

Your sense of smell is also influenced by something called the common chemical sense. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. These nerve endings help you sense irritating substances—such as the tear-inducing power of an onion—or the refreshing coolness of menthol.

What are the smell disorders?

People who have a smell disorders either have a decrease in their ability to smell or changes in the way they perceive odors.

  • Hyposmia is a reduced ability to detect odors.
  • Anosmia is the complete inability to detect odors. In rare cases, someone may be born without a sense of smell, a condition called congenital anosmia.
  • Parosmia is a change in the normal perception of odors, such as when the smell of something familiar is distorted, or when something that normally smells pleasant now smells foul.
  • Phantosmia is the sensation of an odor that isn’t there.

What causes smell disorders?

Smell disorders have many causes, with some more obvious than others. Most people who develop a smell disorder have experienced a recent illness or injury. Common causes of smell disorders are:

  • Aging
  • Sinus and other upper respiratory infections
  • Smoking
  • Growths in the nasal cavities
  • Head injury
  • Hormonal disturbances
  • Dental problems
  • Exposure to certain chemicals, such as insecticides and solvents
  • Numerous medications, including some common antibiotics and antihistamines
  • Radiation for treatment of head and neck cancers
  • Conditions that affect the nervous system, such as Parkinson’s disease or Alzheimer’s disease.

How are smell disorders diagnosed and treated?

Both smell and taste disorders are treated by an otolaryngologist, a doctor who specializes in diseases of the ear, nose, throat, head, and neck (sometimes called an ENT). An accurate assessment of a smell disorder will include, among other things, a physical examination of the ears, nose, and throat; a review of your health history, such as exposure to toxic chemicals or injury; and a smell test supervised by a health care professional.

There are two common ways to test smell. Some tests are designed to measure the smallest amount of odor that someone can detect. Another common test consists of a paper booklet of pages that contain tiny beads filled with specific odors. People are asked to scratch each page and identify the odor. If they can’t smell the odor, or identify it incorrectly, it could indicate a smell disorder or an impaired ability to smell.

Diagnosis by a doctor is important to identify and treat the underlying cause of a potential smell disorder. If your problem is caused by medications, talk to your doctor to see if lowering the dosage or changing the medicine could reduce its effect on your sense of smell. If nasal obstructions such as polyps are restricting the airflow in your nose, you might need surgery to remove them and restore your sense of smell.

Some people recover their ability to smell when they recover from the illness causing their loss of smell. Some people recover their sense of smell spontaneously, for no obvious reason. If your smell disorder can’t be successfully treated, you might want to seek counseling to help you adjust.

Are smell disorders serious?

Like all of your senses, your sense of smell plays an important part in your life. Your sense of smell often serves as a first warning signal, alerting you to the smoke of a fire, spoiled food, or the odor of a natural gas leak or dangerous fumes.

When their smell is impaired, some people change their eating habits. Some may eat too little and lose weight while others may eat too much and gain weight. As food becomes less enjoyable, you might use too much salt to improve the taste. This can be a problem if you have or are at risk for certain medical conditions, such high blood pressure or kidney disease. In severe cases, loss of smell can lead to depression.

Problems with your chemical senses may be a sign of other serious health conditions. A smell disorder can be an early sign of Parkinson’s disease, Alzheimer’s disease, or multiple sclerosis. It can also be related to other medical conditions, such as obesity, diabetes, hypertension, and malnutrition. If you are experiencing a smell disorder, talk with your doctor.

What research is being done on smell disorders?

The NIDCD supports basic and clinical research of smell and taste disorders at its laboratories in Bethesda, Maryland, and at universities and chemosensory research centers across the country. These chemosensory scientists are exploring how to:

  • Promote the regeneration of sensory nerve cells.
  • Understand the effects of the environment (such as gasoline fumes, chemicals, and extremes of humidity and temperature) on smell and taste.
  • Prevent the effects of aging on smell and taste.
  • Develop new diagnostic tests for taste and smell disorders.
  • Understand associations between smell disorders and changes in diet and food preferences in the elderly or among people with chronic illnesses.

Where can I find additional information about smell disorders?

The NIDCD maintains a directory of organizations that provide information on the normal and disordered processes of hearing, balance, taste, smell, voice, speech, and language. To find organizations with information specifically about smell disorders, click on Taste and Smell in the “Browse by Topic” list.

Thank you for your interest in the Taste and Smell Center. You are one of about 2 million adult Americans affected by taste or smell disorders. Unfortunately, very little is known about these problems, which is why our Clinic was established in 1981 with funds from the National Institutes of Health. We evaluate patients with taste and smell problems at weekly clinics, as well as conduct taste and smell research programs here at UConn Health. Treatment is offered when appropriate, although less than a third of patients evaluated here will be determined to have a treatable taste or smell problem.

If you wish to be evaluated here, call 860-679-2804.

What Are the Chemical Senses?

The chemical senses include taste and smell. The perception of a smell occurs when substances in the air pass through the nose and stimulate the olfactory (smell) nerve. The experience of taste, or gustation, occurs when the taste buds in your mouth respond to substances dissolved in saliva. The four basic tastes are salty, sweet, sour and bitter.

What Are Some of the Disorders of Taste and Smell?

  • Anosmia – total loss of smell
  • Hyposmia – partial loss of smell
  • Parosmia – perceiving a smell when no odor is present or perceiving familiar odors as smelling strange
  • Hypogeusia – a diminished sense of taste
  • Dysgeusia – a persistent taste, usually unpleasant

What Are the Causes of Taste and Smell Disorders?

Losses or distortions of taste and smell have many causes such as nasal disease, upper respiratory infections, head injury, neurological disorders, or dental problems. There are some people who have had no sense of smell since birth.

Are Taste and Smell Related?

Taste and smell are two separate senses. However, both contribute to the experience of flavor.

What Is Flavor?

Flavor is what people commonly call the “taste” of food. It is actually a combination of smell, taste, spiciness, temperature and texture. Much of the flavor of food comes from smell, so that when you are unable to smell you have lost much of your ability to experience flavor.

What Can Be Done to Improve the Flavor of Food?

Eating can be more enjoyable when the other aspects of flavor, such as texture, temperature, and spiciness are emphasized. Texture can be enhanced by adding crunchy foods (nuts, croutons, water chestnuts) to your meals. Combining cold and hot temperatures in the same dish (sour cream on a baked potato), as well as trying hot and spicy foods may help to make food less bland. Keep in mind that a pleasant atmosphere and attractively prepared meals can also help to make food more enjoyable.

What Other Suggestions Are There for People with a Taste/Smell Loss?

We would strongly recommend that you equip your home with smoke detectors. Those individuals potentially exposed to gas leaks should consider purchasing a gas detector. Your gas company should be able to supply you with information regarding gas detectors. If not, the Taste and Smell Center can be contacted for this information. In order to guard against eating food you suspect may be spoiled, ask someone else to smell it. If that is impossible, pay particular attention to the dates stamped on most perishable foods and do not consume them after that date.

Your Nose

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A big batch of cookies coming out of the oven. Your gym bag full of dirty clothes. How do you smell these smells and thousands more? It’s your nose, of course.

Your nose lets you smell and it’s a big part of why you are able to taste things. The nose is also the main gate to the respiratory system, your body’s system for breathing. Let’s be nosy and find out some more about the nose.

Nose Parts

The nose has two holes called nostrils. The nostrils and the nasal passages are separated by a wall called the septum (say: SEP-tum). Deep inside your nose, close to your skull, your septum is made of very thin pieces of bone.

Closer to the tip of your nose, the septum is made of cartilage (say: KAR-tel-ij), which is flexible material that’s firmer than skin or muscle. It’s not as hard as bone, and if you push on the tip of your nose, you can feel how wiggly it is.

Behind your nose, in the middle of your face, is a space called the nasal cavity. It connects with the back of the throat. The nasal cavity is separated from the inside of your mouth by the palate (roof of your mouth).

Getting the Air in There

When you inhale air through your nostrils, the air enters the nasal passages and travels into your nasal cavity. The air then passes down the back of your throat into the trachea (say: TRAY-kee-uh), or windpipe, on its way to the lungs.

Your nose is also a two-way street. When you exhale the old air from your lungs, the nose is the main way for the air to leave your body. But your nose is more than a passageway for air. The nose also warms, moistens, and filters the air before it goes to the lungs.

The inside of your nose is lined with a moist, thin layer of tissue called a mucous membrane (say: MYOO-kus MEM-brayne). This membrane warms up the air and moistens it. The mucous membrane makes mucus, that sticky stuff in your nose you might call snot. Mucus captures dust, germs, and other small particles that could irritate your lungs. If you look inside your nose, you will also see hairs that can trap large particles, like dirt or pollen.

If something does get trapped in there, you can probably guess what happens next. You sneeze. Sneezes can send those unwelcome particles speeding out of your nose at 100 mph!

Further back in your nose are even smaller hairs called cilia (say: SILL-ee-uh) that you can see only with a microscope. The cilia move back and forth to move the mucus out of the sinuses and back of the nose. Cilia can also be found lining the air passages, where they help move mucus out of the lungs.

Sniff, Sniff, Take a Whiff

The nose allows you to make scents of what’s going on in the world around you. Just as your eyes give you information by seeing and your ears help you out by hearing, the nose lets you figure out what’s happening by smelling. It does this with help from many parts hidden deep inside your nasal cavity and head.

Up on the roof of the nasal cavity (the space behind your nose) is the olfactory epithelium (say: ol-FAK-tuh-ree eh-puh-THEE-lee-um). Olfactory is a fancy word that has to do with smelling. The olfactory epithelium contains special receptors that are sensitive to odor molecules that travel through the air.

These receptors are very small — there are about 10 million of them in your nose! There are hundreds of different odor receptors, each with the ability to sense certain odor molecules. Research has shown that an odor can stimulate several different kinds of receptors. The brain interprets the combination of receptors to recognize any one of about 10,000 different smells.

How Signals Get Sent

When the smell receptors are stimulated, signals travel along the olfactory nerve to the olfactory bulb. The olfactory bulb is underneath the front of your brain just above the nasal cavity. Signals are sent from the olfactory bulb to other parts of the brain to be interpreted as a smell you may recognize, like apple pie fresh from the oven. Yum!

Identifying smells is your brain’s way of telling you about your environment. Have you ever smelled your toast burning? In an instant, your brain interpreted the smell and a problem and you knew to check on your toast.

You learned to associate a certain smell with burning and now your brain remembers that smell so you recognize it. Your sense of smell also can help you keep safe. For example, it can warn you not to eat something that smells rotten or help you detect smoke before you see a fire.

Tastes Great!

Most people just think of the tongue when they think about taste. But you couldn’t taste anything without some help from the nose! The ability to smell and taste go together because odors from foods allow us to taste more fully.

Take a bite of food and think about how it tastes. Then pinch your nose and take another bite. Notice the difference? It’s just another reason to appreciate your knockout of a nose!

Reviewed by: KidsHealth Medical Experts

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