Show Mobile Navigation
Facts |

10 Experiments That Reveal Amazing Facts About The Sense Of Smell

by Yuliya Geikhman
fact checked by Jamie Frater

Humans don’t have the best sense of smell. We smell with about five or six million cells, compared to a rabbit’s 100 million or a dog’s 220 million cells. Even so, several studies have shown that our sense of smell picks up cues that we don’t even notice on a conscious level. The animal and plant worlds also have some secrets to reveal about the sense of smell.

10 The Autism Sniff Test


Autism is difficult to diagnose. Currently, there is no objective medical test for autism spectrum disorder, so doctors rely on studying a child’s behavior and development instead. According to the Centers for Disease Control, the diagnosis of autism skyrocketed to 1 in 88 US children in 2012, up from 1 in 166 just four years earlier.

Although some of these children with newly diagnosed autism may have been incorrectly overlooked in the past, there is also a good chance that some are being misdiagnosed. A medical test for autism would provide a less subjective method of determining which children truly have the disorder.

That’s where our sense of smell comes in. When you pass a bouquet of freshly picked flowers, you sniff deeply to take in the scent. When you enter a public bathroom badly in need of a cleaning, you take shallower breaths to keep the smell out.

One study showed that autistic children don’t make this distinction. They breathe and smell the same way regardless of the kind of smell to which they’re exposed. In the lab, a sniff test was 81 percent accurate in identifying children with autism at an average age of seven.

The autism sniff test is not ready for the field yet. But if it becomes viable, it could make huge strides in accurately detecting autism. Its nonverbal nature means that it may be used to detect autism in toddlers and babies, allowing for earlier intervention.

9 Cat Urine And Baby Mice


In an experiment that must have looked a lot like a Tom and Jerry cartoon, scientists found that mice exposed to a strong smell of cat urine when they’re young are less likely to escape from cats as adults.

When first exposed to the smell, the mice in the study were less than two weeks old, a time when they were still fed milk. As a result, they learned to associate the cat urine smell with comfort and security. Even so, exposed mice still had a stress response to smelling a cat nearby, but they were not as likely to run from it.

This mouse research is an interesting mirror of human “priming,” which happens when some signal—a touch, a sound, even a smell—changes the way we process things subconsciously. Studies have shown that something as trivial as the temperature of our coffee can influence the way we perceive people.

In animals or in humans, smells can change the way we feel and act, regardless of what our instincts say.

8 The Armpit Effect


In 1995, Swiss zoologist Claus Wedekind gathered 49 women and asked them to smell the sweaty, two-day-old T-shirts of 44 men. No, this wasn’t some kinky party. It was an experiment that showed just how much our sense of smell impacts our choice of partner.

The study showed that women subconsciously choose their mates by smell. Without realizing it, we identify someone’s chemical signature when we smell them and are instinctively attracted to people who complement our own smell.

Our goal as a species is to create healthy offspring. This experiment showed that smell plays a large part in reaching that goal. A woman is more attracted to the smell of men with major histocompatibility complex (MHC) genes that are different than her own. Parents with different MHC genes have children with stronger immune systems, so it appears that a woman can subconsciously detect through smell who would be the best mate for her.

This experiment also explains why women on birth control pills often find they’re no longer attracted to their partners once they go off the pill. Using birth control pills makes a woman more attracted to a man who has a smell signature that’s similar to her own. This may occur because the pills’ effect of mimicking pregnancy makes a woman instinctively more attracted to nurturing relatives rather than someone who would be the best mate.

Whether a woman is attracted to her partner’s smelly armpits also depends on at least one other factor: A variation on the armpit sniff test showed that women were happier when they smelled the sweat created by happy men. It has already been shown that negative emotions can be transferred through smells, but now we know you can share your joy through your sweat, too.

7 Old Book Smell


Open an old book and you’ll be greeted by a very specific scent. That’s not just the bibliophile in you rejoicing at holding an old book. There’s a science behind that well-known smell, which may hold the key to preserving old books.

When we use current methods of dating an old book or document, we have to destroy a small part of that book or document. The more common methods of dating include analyzing a small portion of ink or using a fragment of the document for radiocarbon dating.

However, that old book smell may have given us a less intrusive way to test the age of a book. The smells are created by “volatile organic compounds,” which are released when you turn the pages. These compounds can tell researchers a lot about the age and condition of the paper.

During a sniff test of some old documents, researchers isolated 15 compounds that may help to detect the level of damage sustained by the paper tested. In theory, smelling the pages of an old book can help to determine the stage of degradation of the paper, which in turn can help to better preserve it.

6 Freshly Cut Grass


The smell of freshly mowed grass has been shown to relax and de-stress people, so much so that a University of Queensland scientist has bottled it into an “eau de grass” perfume. But why does a mowed lawn smell so good?

In reality, the smell you find so calming and refreshing is a distress signal. A study from 1983 found that when pest insects attack certain trees, those trees give off a signal that alerts nearby trees of the danger.

A more recent study from 2010 revealed a complicated chain reaction from the freshly mowed grass smell. When plants are attacked by pests, they give off a smell that attracts parasitic wasps, which lay their eggs in the pests and protect the plants.

The US Department of Agriculture has invested nearly half a million dollars into studying this SOS compound because these signals may also protect plants from drought. Researchers aren’t sure yet how this happens, but understanding the role of this distress signal may help to protect plants one day.

5 Asparagus Urine


Asparagus is known for its health benefits because it contains vitamins A, B6, and C as well as folic acid, potassium, thiamin, and antioxidants. The spears also have their own council in Australia. But asparagus is even better known for smelly urine.

If you’ve ever eaten asparagus, you may have noticed that your urine smells odd afterward. No one is sure what causes this smell. But the leading candidate is asparagusic acid, a substance unique to asparagus and mostly blamed for the smell because no one can prove otherwise.

However, if you’ve never noticed a strange smell after eating asparagus, you might not be able to detect the smell. Or maybe you don’t make it. Scientists aren’t sure, but they felt it was important enough to investigate.

Many studies have been conducted on asparagus urine, each with a different conclusion. About 50 percent to 92 percent of people don’t produce the smell, depending on which study you consult. Other people do create the smell but seem unable to detect it.

So what’s going on? The wildly different numbers were reported by studies conducted in different places. That means it’s possible that whether you can smell or make asparagus-scented urine depends on your ethnicity.

In July 2010, researchers took one more stab at sorting the nonproducers from the non-detectors. According to this study, 8 percent of people don’t produce the smell, and 6 percent can’t detect it.

Despite the findings, the study points out that it’s impossible to test an unknown substance. As a result, the cause of asparagus urine remains a mystery to everybody.

4 Smelling Delicious To Mosquitoes


You may be the one person who gets bitten by mosquitoes when everyone else remains unscathed. What makes you so delicious to these bloodsucking pests? It can be anything from your blood type to whether you just enjoyed some cold beer.

An infection with malaria will also make you smell irresistible to mosquitoes. A 2014 study found that the malaria parasite changes the way people smell, making them more attractive to mosquitoes. The more mosquitoes the infected body attracts, the more effectively the disease can spread.

Since mosquitoes are already known as the transmitters of the deadly malaria disease, researchers are looking for a way to make humans smell less attractive to the pests. One team of researchers at Penn State University received a grant in 2009 from the Bill and Melinda Gates Foundation to research a fungus that can dull a mosquito’s sense of smell, making it hard for them to find human hosts on which to prey.

Another group from the Howard Hughes Medical Institute has managed to genetically engineer mosquitoes to respond differently to odors, including those of humans and the insect repellent DEET. But it appears that the key to fighting malaria may be the mosquito’s sense of smell.

3 The Smell Of White


White is not a color. What we call “white” is really the combination of all the wavelengths of visible light, which essentially cancel each other out. We see white and hear white noise, but what happens when you create a white smell?

One study tried to create a “white smell” composed of 30 or more different odors. Alone or in small groups, it’s possible to detect the separate smells. But once you reach a mixture with enough scents, all the smells blend together into one neutral odor.

The white smell was given the name “Laurax” and unleashed onto study participants. People described Laurax as “not pleasant, but not unpleasant.” It didn’t matter which 30 odors were mixed together. As long as the mixture contained at least 30 scents, people identified the resulting smell as Laurax. Even if the two Laurax mixes had none of the same components, they still smelled the same.

This shows that not only does the concept of white carry over into the sense of smell but also that we may detect smells differently than once believed. It’s widely assumed that our sense of smell works by analyzing different components of a scent and combining them into a whole. This study implies that our noses pick up on the whole, not the parts.

2 Anxiety And Smell


Stress and sweat go hand in hand. Sweating under pressure is a common reaction for many people, although scientists couldn’t explain it at first. They now believe that stress sweat was once an automatic way to warn others around you of potential dangers.

Smelling bad when you’re stressed may be expected, but it turns out that you’ll also smell well. A 2013 study showed that being anxious gives us a better sense of smell. The study found that the more anxious a person is, the better he becomes at discriminating between negative smells. This is most likely a holdover from when smell was important to survival.

Not only does our sense of smell become better when we’re anxious, but we also perceive neutral smells as worse. So the more stressed we are, the worse the world around us smells. The worse (and more threatening) things smell, the more anxious we become. If we can learn more about this negative feedback loop, it might help us to develop better treatments for anxiety and depression.

1 Loss Of Smell Means Loss Of Health


If you had to lose one of your senses, which would you choose? Many people would opt to lose their sense of smell, which seems less important than hearing or sight. However, losing your sense of smell can signify the beginning of many other health problems.

There have been many studies exploring the connection between your sense of smell and your mental and physical health. In October 2014, one study found that older people with severe deteriorations in their sense of smell were twice as likely to be dead within five years.

According to some research, our sense of smell begins to deteriorate when we’re in our twenties, with some odors losing their potency when we’re as young as 15 years old. But a drastically declining sense of smell in adults can be an early warning sign of Alzheimer’s disease, Parkinson’s disease, or even depression.

A 2012 study also found that psychopaths are more likely to have an impaired sense of smell. Of course, this doesn’t mean that everyone with a poor sense of smell is psychotic. But it does mean that the nose knows more than we think it does.

Yuliya can recall smells from years ago, and her favorite smell is that moment right before it starts to rain. You can hire her to write words for you here.

fact checked by Jamie Frater