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SmellHumans may be able to distinguish between more than a trillion different odors—extending our awareness beyond our immediate surroundings to enable us to detect gas leaks or pick up the scent of someone who just left the room. Smell is one of our most powerful senses. It's better than sight at evoking strong memories because of the anatomy of the olfactory system, which allows neural signals about smell to bypass an area of the brain called the thalamus, so the olfactory bulb in the forebrain connects directly to brain areas that manage emotion and memory.
When we smell something, we are actually breathing in tiny molecules that stimulate specialized olfactory neurons high inside the nose. Our olfactory system allows us to detect and discriminate among these substances, and our brain assigns these scents an emotional tag that influences our thoughts and actions—eat this, avoid this, flee.
The anatomy of the nose and throat makes it possible to decipher complex flavor profiles because chemicals from the foods we eat travel from our mouths and throat to the olfactory neurons high inside the nose. Then, the brain attaches labels to those scents, just as it does with scents from the external environment.
Partial or total loss of the sense of smell—hyposmia and anosmia, respectively—can significantly impact quality of life and typically occurs due to disease or trauma. Anosmia occurs among roughly 3% of the US adult population over age 40. Sometimes this issue resolves on its own, but steroids and long-term smell retraining can often help. Phantom odor perception—smelling odors that aren't actually present—occurs in roughly 7% of Americans over age 40.Explore Smell
What we've found
Humans can't smell the inside of their nose due to olfactory fatigueOnce a person is accustomed to a specific odor, their neurons have trouble continuing to respond to that smell because of that familiarity. That's why humans may not notice when their house smells like trash until they leave the house and then return to it. Loss of sense of smell is a common symptom of COVID-19 infectionIn 2020, researchers discovered why this occurs. The virus that causes this infection attacks the cells that support smell-detecting neurons. Once infection clears, the sense of smell typically returns, though the exact timeline for that differs by patient. (Some users may experience a paywall.) USA TODAYSmell is a robust memory cue for individuals with Alzheimer's diseaseOdor is more effective than both visual and verbal cues for triggering autobiographical recall in Alzheimer's disease, according to 2021 research. Psychology TodaySmell retraining can help people with anosmia learn to smell againOlfactory training, which involves repeatedly smelling a selection of strong odors, teaches your brain to familiarize itself with experiencing smells over a lengthy period, typically multiple months. This can be useful for patients who lose their sense of smell for myriad reasons. Good RxA stand-in 'nose' may help people with anosmia to smell certain odorsIn a 2025 paper, researchers reported they'd created a proof-of-concept device that bypasses typical olfactory pathways and instead exploits an alternative—the trigeminal nerve in the nose—to detect a few strong scents. The nerve typically helps detect the temperature of inhaled air or the presence of irritants. (Some users may experience a paywall.) ScienceHeightened sense of smell during pregnancy is not yet well understoodBoosted smell powers and strong reactions to them are often reported beginning around the six-week mark of pregnancy. Researchers say hormonal changes likely play a role, but the change remains poorly understood. The BumpHumans can track smells on the ground quite well—our ability to crawl is a limiting factorAs part of a scientific bet, neurobiology researchers dragged a chocolate bar across the grass and sought to see if a human could track it—she could. This led to a more in-depth experiment on human olfactory capabilities and behavior when other senses were blocked. Huberman LabOur sense of smell affects what foods taste like and how we perceive itScent stimulates our olfactory sensor neurons high in the nasal cavity, and the brain attaches labels to those scents. But when we eat, chemicals from the foods travel from our mouths and throat to those neurons. We have roughly 400 odor receptors, and they can be used to decipher more than 10,000 different odors (or more than one trillion by some calculations), including the nuances of different foods. TED-EdRead the academic article explaining how ancient smells can be dissected and recreatedThis paper explores how biomolecular data on past scents can be teased out and then transformed into olfactory museum experiences, adding another component to our understanding of archaeology. Frontiers in Environmental ArchaeologyScientists are reconstructing ancient smells—including a 3,500-year-old ancient Egyptian mummyResearchers explain how they have recreated the scent of ancient Egyptian mummies and enabled museum-goers to experience that scent on specialized cards. The exhibit will be at the Royal BC Museum in Canada in June 2026. Science FridayNewborns have a strong sense of smellBabies are drawn to their mother's smell—and the particular odor of their mother's breast milk—within days, even as their vision remains blurry for months after birth. In the womb, the olfactory center also forms in the early stages of development. Children's Hospital of PhiladelphiaRoughly 15 of every 1,000 people in the US have smell disordersAnosmia is a lack of a sense of smell. It can be present at birth, related to diseases including Parkinson's, Alzheimer's, and COVID-19, or have unknown causes. Journal of the American Medical AssociationAnosmia is the total loss of the sense of smellThis type of loss—due to disease or trauma—has ripple effects, including an altered or limited sense of taste. This video details the anatomy and physiology of our sense of smell and taste and how these senses are interrelated. CrashCourseCorynebacterium species are particularly responsible for our funky smellMyriad bacteria contribute to our body odor, but research suggests that Corynebacterium species are strongly associated with the bad smells emanating from adults. Staphylococcus and Cutibacterium genera may also play leading roles. National Library of MedicineTyphoid smells like freshly baked brown breadCertain ailments are associated with documented scents, including diabetes, Parkinson's disease, and typhoid. The skin of people with yellow fever, for example, can smell like a "butcher shop." Gross ScienceRead a study documenting how 'old people' smell increases with ageAnalysis of body odors from individuals aged 26 to 75 confirmed that 2-nonenal, an unsaturated aldehyde with an unpleasant, greasy, and grassy odor, was detected only in subjects aged 40 and older. Journal of Investigative Dermatology'Old people' smell is real—it's a chemical buildup when fatty acids on the skin oxidizeThe chemical composition of body odor seems to change with age. Later in life, we harbor higher concentrations of a chemical compound called 2-nonenal that forms when omega-7 fatty acids on the skin oxidize, and the skin's natural antioxidant defenses weaken. Commonly called "nonenal", it's the smell widely associated with aging, and it's often described as a grassy or greasy odor. Assisting Hands Home CareFear has a specific 'smell'—at least to machinesThis excerpt from a Mythbusters episode takes on the smell-of-fear question, comparing the sweat composition of individuals exposed to snakes, rats, and scorpions with that of people exercising. Molecularly, the sweats are different to a gas chromatography machine, but to most noses would be indistinguishable. DiscoveryDogs smell a lot of stuff we can't, including bed bugs and chemicals in electronic devicesIn addition to identifying medical smells and tiny insects like bed bugs, dogs can also detect electronic storage devices. These tools often contain triphenylphosphine oxide, a chemical used to prevent overheating. Reader's DigestCarboxylic acids are one reason teens are smellyScientists compared the smells of babies and teenagers and identified some of the compounds that make teens smelly. Carboxylic acids present in teens, they wrote, seemed to give off an "earthy, musty, or cheesy" scent. This 2024 research could help inform future odor-control products. Phys.orgHereditary hyperosmia is the official term for being a super-smellerSome sniffers with this rare trait may be more sensitive to pleasant smells, while others may be more attuned to unpleasant scents. Some research suggests that certain genetic mutations are associated with a heightened sense of smell. The ConversationMost people with East Asian ancestry are genetically predisposed to be less smellyA gene variant found in 80%-95% of individuals with East Asian ancestry reduces armpit bacteria and related odors. People with this nonfunctioning ABCC11 gene variant lack a protein that transports molecules, including sweat, across cellular membranes, so their armpits are starved of sweat that bacteria may have metabolized to help them multiply. BBC World ServiceA super-sniffer smelled her husband's Parkinson's disease years ahead of symptomsShe discovered she could smell diseases, including Parkinson's, tuberculosis, Alzheimer's, cancer, and diabetes. Working with an analytic chemist, she's learned she can smell subtle changes in odor—ones that smell consistent across individuals with the same disorder—even before symptoms manifest. Invisibilia On average, people smell worse if they're sickFor a small 2014 research study, a panel was tasked with sniffing the smelly t-shirts of people who had been injected with a compound known to activate the immune system and those of controls without the shot. It found that those who were acting as if unwell (due to the injection) generally smelled worse. Subsequent work found that those who sniffed unpleasant odors had a mild immune response of their own—perhaps to protect them from disease. (Some users may experience a paywall.) CNNSweat doesn't smell, but bacteria multiply in moist environments—and cause an odorBody odor is associated with sweat, but odor actually arises from the bacteria that multiply in moist environments on your skin. Hormones, medications, food, and body hair can all affect body odor. Cleveland ClinicJust because leftovers look and smell okay doesn’t mean they’re safe to eatDespite what the sniff test is telling you, older leftovers should probably be trashed. Pathogens that cause illness don’t usually affect the taste, smell, or appearance of food (though if they look bad, you should chuck them as well). Scientists recommend tossing leftovers within a few days even if they appear to be fine. Washington State Department of HealthMuted smell and taste in microgravity complicate meal enjoymentAstronauts primarily consume freeze-dried meals, which are rehydrated with water recycled from urine and perspiration, directly from bags. Condiments and select cultural items from crew members can enhance the meal experience by boosting flavor. Many individuals report experiencing "food fatigue" due to a lack of fresh produce, limited menu variety, and lingering scents. Ologies With Alie WardFremont, Ohio, produces over one billion pounds of Heinz ketchup every year, often sending the smell of the condiment through the small cityMost of the United States' Heinz ketchup is produced at the northeast Ohio plant, which has been open since 1937. MidstoryOdor blockers use nonpolar oils to trap smelly polar moleculesIn the case of feces, gut bacteria produce compounds such as skatole and hydrogen sulfide, which the brain registers as unpleasant. Because oils do not dissolve in water, they can be used to create a layer on the surface that prevents smelly compounds underwater from escaping into the air. Chemistry For Your LifeScientists determine the smells of objects in outer spaceUsing spectrographic techniques, scientists determine the chemical composition of planetary atmospheres, comets, and other objects in space. Combining these chemicals in labs on Earth has revealed locations in space that smell like nail polish remover, rotten fish, and urine. BBCAstronauts agree: The moon smells like gunpowderTwelve astronauts have walked on the moon to date, and they all agree that our lunar neighbor smells like gunpowder. Scientists argue this scent comes from unstable minerals that cling to their suits and the rocks they return to the ship. Notwithstanding, space itself has a different smell, often compared to steak or metal, which experts believe, rather poetically, is the smell of dead stars. Smithsonian MagazineThe superpowers of your sense of smellPeople regularly rank their sense of smell as the one they'd miss the least if they had to lose one. Notwithstanding this impoverished reputation, olfaction—as it is known medically—is one of the earliest to form in humans, and is intimately tied up with the memory function, capable of stirring childhood images with one wisp of fresh baking or flowers. Unlike some other cells, your olfaction nerve cells regenerate regularly, as well, making this sense particularly resilient to damage. The ConversationThe most unique-smelling places on EarthHave you ever picked a travel destination by smell? This Atlas Obscura piece cultivates a list of the most distinct-smelling spots in the world. Learn about these obscure scents to potentially book a trip to a spring that smells like rotten eggs, or a desert valley filled with frankincense trees. Atlas ObscuraWhy your wine smells unpleasantEver had the experience of receiving a bottle of wine with a janky, less-than-favorable odor? This Esquire article ventures to answer this question and offers the explanation that the culprit is likely corked wine. Read to understand why corks can create a moldy or musty scent, and feel emboldened to send a corked bottle back for something with improved quality. EsquireWine connoisseurs say proper tasting requires looking, smelling, tasting, and thinkingTasting wine can be intimidating, which is why Wine Folly cofounder Madeline Puckette breaks down the four steps in this helpful video, encouraging viewers to pour a glass and follow along. Wine FollyDark chocolate’s delicious smell is a mix of vanillin, vinegar, and…sweat?Scientists have worked out the chemistry of dark chocolate’s smell and reconstructed the aroma. Science NewsA 'fishy' scent does lead to mistrustIn experiments where people were exposed to a literal fishy smell they were less willing to cooperate with others in economic games requiring trust, but that wasn't the case when they were exposed to another bad odor—the smell of flatulence. Psychology TodayHumans may be able to distinguish more than one trillion scentsThat's according to one estimate published in 2014. This figure far exceeds earlier estimates of a human smelling ceiling around 10,000 odors. The newer figure is derived from experiments in which volunteers agreed to sniff varying scents. Researchers mixed odor components and had volunteers sniff the brews to detect subtle scent differences. (Some users may experience a paywall.) ScienceScent is a stronger memory trigger than sightSmell is imbued with more emotion than visual memories, and research indicates that smell triggers a significantly greater effect on amygdala activation. Scientists believe these powerful responses occur partly because smell signals bypass the thalamus and go directly to the amygdala and hippocampus, brain areas involved in emotion and memory. Cleveland Clinic1 in 15 adults over age 40 experience phantom odorsThis phenomenon was measured in a 2018 study that examined the prevalence and risk factors for phantom odor perception. Older adults were less likely to experience these phantom odors as they age, just as their overall sense of smell declines. Women are more likely than men to perceive phantom odors. National Institute on Deafness and Other Communication DisordersAmericans spent $6.6 billion on body odor products in 2023This high figure from Euromonitor, a research firm, suggests Americans spent more on deodorant than in any other country. Beyond deodorant, there's also growing interest in "whole body" deodorant designed to mask smells from various parts of the body beyond the armpit. Forbes'Sweat dating' is a dating approach where partners specifically select by body odorWith dedicated events in major cities around the world, "sweat dating" offers people the chance to judge if a potential partner's smell is a match. Participants show up for an event, do calisthenics, wipe themselves with a cotton pad, and then place the smelly pad in a numbered jar for potential partners to sniff. This Podcast Will Kill YouNorway is responsible for salmon sushiJapanese sushi did not include salmon until the mid-1990s because Pacific salmon was known to contain parasites. Norway, meanwhile, had an abundance of Atlantic salmon, which was safe to eat raw. The country smelled an opportunity and launched Project Japan, which successfully convinced the country that Atlantic salmon was safe to include in its cuisine. Great Big StoryBenjamin Franklin once wrote a satirical essay about passing gasThe Founding Father was asked to judge a contest for the Royal Academy of Brussels, but was incensed by one of the contest's questions, which he believed was highly impractical. In response, he wrote a piece suggesting that the most essential problem for scientists to solve was the "fetid Smell" that came with passing gas. The Kidd Creek Mine in Canada houses the world's oldest isolated waterThe mine sits on the Precambrian Canadian Shield—an ocean floor dating back 2.7 billion years. Exhibiting a musty smell, the water is 10 times saltier than seawater and offers insights into Earth’s ancient seabed. ZME ScienceBefore it was a drink, coffee was used for handwashingFive centuries before the caffeinated drink was consumed, coffee beans were used for their aromatic quality. One 10th-century text explains how it "obliterates greasy smells of food on hands and whatever of sweets and fats. Whether traveling or at home, neglect not to wash your hands with it." Atlas ObscuraFireflies light up to provide mating signals and warnings to predatorsVariations in the illumination patterns and flight paths while emitting light have been observed across firefly species. Some species instead rely on pheromones if they are primarily active during the day or have lost the ability to illuminate. Science FridayThe ginkgo tree is a living fossil that has not changed in over 200 million yearsHaving outlived the dinosaurs, the tree has no living relatives as the only surviving species of the genus Ginkgo. Its growth in undisturbed environments, pollution resistance, and foul-smelling seeds may have contributed to its survivability. Yale E360Seven incredible discoveries of long-lost artThe art of great masters sometimes disappears for decades, even centuries, only to reappear in the most surprising places. Basements, attics, thrift shops, or even the original museum from which the piece was stolen can all turn up a Caravaggio, van Gogh, or a Qing dynasty vase (or two). Here are seven surprising examples. Artnet NewsElectric vehicles have been around since the 19th centuryThe first EVs ran on rechargeable lead-acid batteries, which could travel 60 to 80 miles on a single charge. Women preferred these vehicles, which were quieter, less smelly, and did not require turning a hand crank to start the engine. 1440
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