Humans 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.
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The nose structure plays a key role in filtering air before it enters our lungs and makes sure that the air temperature and humidity are also suitable for the body.
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.
Smell 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.
This 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.
Anosmia 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.
Babies 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.
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.
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.)
In 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.
Researchers 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.
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