Humans can't smell the inside of their nose due to olfactory fatigue

Smell retraining can help people with anosmia learn to smell again

Olfactory 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.

Humans may be able to distinguish more than one trillion scents

That'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.)

Our sense of smell affects what foods taste like and how we perceive it

Scent 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.

Loss of sense of smell is a common symptom of COVID-19 infection

In 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.)

1 in 15 adults over age 40 experience phantom odors

This 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.

Humans can track smells on the ground quite well—our ability to crawl is a limiting factor

As 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.

A dog's central sniffing organ is many times bigger than a human's

The olfactory epithelium, located high up within the human nose, is home to millions of olfactory neurons. A dog's olfactory epithelium is much larger—and has more neurons—than a human's, which helps to explain the animal's superior sniffing ability.

'Old people' smell is real—it's a chemical buildup when fatty acids on the skin oxidize

The 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.

Hereditary hyperosmia is the official term for being a super-smeller

Some 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.

A super-sniffer smelled her husband's Parkinson's disease years ahead of symptoms

She 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.

Fear has a specific 'smell'—at least to machines

This 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.

Always forget a face? The science of face-blindness

Faces and names don't always go together in some people's minds. While everyone forgets other peoples's names occasion, people diagnosed with prosopagnosia can't recognize faces, much less names. Even friends can family members can appear to be strangers. This article covers the diagnosis and issues attendant to prosopagnosia and its sufferers.

How does the body know where it is in space?

Close your eyes and touch your nose. How did you know where your nose was? How could you tell where your hand was? That's proprioception, the sense that keeps your brain apprised of the body's position and movement. This article explains how this sense works, what happens when people don't have it, and what we know about it.

Over time, people develop a resistance to spicy foods

TRPV1 is a receptor in the body that detects potentially harmful things and responds in a variety of ways, including sweating, tearing up or a runny nose. Over time, more exposure to spicy foods can build up a resistance that minimizes these reactions.

If hearing is damaged, the brain may amplify remaining sounds, perhaps causing tinnitus

Recent mouse brain and ear imaging revealed that the creature compensates for hearing loss by sending signals to the cochlea in the inner ear. This triggers nerve fibers in the inner ear to increase volume and become more sensitive. Learning about these boosted-sensitivity messages from the brain to the cochlea—if they're similar in humans—might help explain tinnitus and fuel experimental approaches to turn down that sensitivity.

The doorway effect is when people forget their task when entering a new space

The "why did I come in here?" feeling after walking into a room comes from the brain creating event boundaries to organize memories. Mentally revisiting a previous room can help recall tasks and reverse memory loss. (Some readers may experience a paywall.)

How humans breathe without thinking about it

We breathe without thinking about it thanks to the body’s respiratory system and autonomic nervous system, which controls vital functions. Breathing transports oxygen to the body’s cells to keep them working and clears the body of carbon...

Muted smell and taste in microgravity complicate meal enjoyment

Astronauts 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.

Age, stress, and neurological disorders can prevent memory formation and recall

Neurons transmit signals between one another at sites called synapses. Repeated interactions at these sites improve the efficiency of signal transmissions, making memories involving sensory data associated with those neurons easier to recall. Biochemical factors impacting these synaptic interactions affect memory quality.

Why some people have allergies

Why do some people have allergies while others don’t? One theory suggests allergies are a relic of our evolutionary past. Our immune system, once primed to fight parasites, now mistakes harmless substances for threats.

What happens to your brain when you burn out?

You've probably heard of burnout, also known as the feeling of exhaustion that happens after a long period of being overwhelmed or stressed. It's often associated with work and careers, but other parts of life, like parenting, can cause burnout, too. Scientists are figuring out what happens, biochemically speaking, in the brain when burnout hits—and spoiler alert, it includes a neurotransmitter called glutamate. Watch this video to learn more.

Stuffy nose congestion occurs because of swelling of the inferior turbinates

These structures in the nose above the nose hairs swell and shrink constantly and are affected by head position. They can fill with blood during illness, causing the feeling of congestion, but also when a person changes position, especially when lying down. Medications can be used to shrink them, providing temporary relief.

Cells cannot grow forever due to escalating inefficiency in transporting chemicals

As cells get larger, their volume grows much faster than the surface area through which nutrients and waste products pass, creating a bottleneck that eventually causes cells to die. This forces nearly all organisms visible to the naked eye to comprise enormous numbers of smaller cells, such as the approximately 30 trillion found in the average adult human.

Overuse of opioids can lead to hypersensitivity to pain

Opioid misuse can lead opioid-induced hyperalgesia, where the body becomes increasingly sensitive to pain. The body produces its own opioids as a way to temporarily block pain signals. When met with external opioid use, the body ratchets up pain sensitivity to ensure it senses the pain necessary to trigger its own response.

The average American likely doesn’t notice how many ads they’re targets of per day

The average American is targeted with roughly 5,000 ads each day—but the conscious mind likely isn’t capable of recalling the majority of those. Even still, many consumers have reported ad fatigue due to the near-constant onslaught of ads.

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

When a Paris department store hesitated to sell Estée Lauder's perfume, she 'accidentally' broke a bottle, causing the smell to spread throughout the store and shoppers to start asking to buy the scent.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

Watch how algorithms can be designed to train themselves and self-improve without human input, to the point where the optimized code is too complex for programmers to understand.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

Despite being favored by 87% of Americans, Congress does not have term limits.

Frank Lloyd Wright's houses are historically hard to sell because they're old, subject to local landmark commissions, and often unfashionable

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

Comedy legend Catherine O'Hara, star of 'Schitt's Creek' and 'Home Alone,' quit 'Saturday Night Live' after just one week to return to her old job.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

Existentialist writer Jean-Paul Sartre coined the famous phrase 'Hell is—other people' in his play 'No Exit'

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.

The Nasdaq's 'Magnificent 7' companies are responsible for roughly 40% of the Nasdaq 100 index's gains, while the remaining 93 companies account for the other 60%.