Why Do Some People Have a Heightened Sense of Smell?

In the middle of dinner, the faint whiff of something burning in the kitchen might go unnoticed by most people, but others may catch the smell instantly. Their noses are a little sharper, tuned to detect even mild traces of smoke, perfume, or additional smells long before other people notice.

Such super smellers have a heightened sense of smell—hyperosmia—compared to the average person. A complex interplay of genetics, brain anatomy, or medical conditions dictate a person’s sensitivity to smell.^1,2 Studying the factors that influence the sense of smell can help scientists better understand olfactory circuits in the brain. This can pave the way for the development of treatments for loss of the sense of smell—anosmia—and offer detailed insights about why anosmia could be an early indicator of conditions like Parkinson’s disease.

How Do People Smell Things?

Odor molecules bind to receptors on olfactory sensory neurons within the nasal cavity, triggering a biochemical cascade that results in transmitting a signal to the brain. “Then there are various areas in the brain that help to extract the code that those cells have made, of what those odors are, and put it back together…to give you an overall perception of the smell,” explained Steven Munger, an otolaryngology researcher who studies the molecular and cellular basis of odor detection at the University of Virginia.

Munger noted that super smellers’ noses may pick up more faint traces of odor molecules. “But it may also be that the brain has changed [due] to…hormones or autoimmune disease or various other things, that may make you more sensitive in your perception of those odors,” he added.

How Scientists Study a Super Sense of Smell

Scientists use a variety of methods to pinpoint the causes behind hyperosmia. Brain scans revealed that compared to people with an average sensitivity to smell, super smellers have increased gray matter volume in the brain regions crucial for olfactory information integration and odor learning and memory.^2,3

Studying genetic variants that super smellers may carry offered more clues. “Humans have about 400 different genes that encode odor receptors,” explained Munger. “And every one of us probably has at least a few of those genes that are nonfunctional, that can't make a receptor, and sometimes that results in our inability to detect certain compounds.” Conversely, some genetic variants may increase a receptor’s sensitivity to certain compounds.

For instance, scientists found that people who were hypersensitive to a sweaty odor carried an intact copy of the gene OR11H7P encoding an olfactory receptor.⁴ In contrast, those who were not sensitive to the odor had mutations in this gene. In another study, scientists found that people with an intact odor receptor gene OR7D4 were more sensitive to the smell of some pheromones.⁵

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Variants in genes other than those encoding olfactory receptors can also manifest as hyperosmia: A boy with increased sensitivity to smell carried a duplication in the promoter region of a gene called anosmin-1 (ANOS1), which regulates the growth and migration of olfactory neurons during neurodevelopment. Those with loss-of-function mutations in the gene experience anosmia.¹

Some studies also suggest that women tend to have a more sensitive nose than men.⁶ “For all people, the sense of smell diminishes over age,” said Munger. “Men are more dramatic in that loss than women.”

He noted that a combination of genetic and behavioral factors—such as the likelihood of exposure to industrial toxins or solvents—may underlie this. “We really need to do large studies, which tends to be challenging, to really know to what extent there are sex differences,” he said.

Sense of Smell and Medical Conditions

Lyme disease-causing bacteria may sometimes affect the nervous system, culminating in neurological complications such as meningitis.⁷ In a small study, researchers found that 50 percent of the people who acquired this tick-borne illness also developed hyperosmia.

While some medical conditions can cause hyperosmia, some neurodegenerative disorders like Parkinson’s disease cause anosmia.⁸ “Smell loss appears in most Parkinson's patients, and does so years before the motor symptoms do,” said Munger.

While loss of sense of smell could be an early indicator of such conditions, Munger noted that scientists still do not completely understand some basic principles underlying the sense of smell. His team is interested in learning how much variability people show in detecting odors throughout the day or through different seasons. “Understanding how smell normally varies under all these different conditions will allow us to better use diagnostic tools to understand when someone's smell is getting worse or getting better and [how it is] related to other things.”