Real Girls: Why your sense of smell is stronger at certain times of day


	August 25, 2024

Original photo by Evheniia Vasylenko/ iStock

Your sense of smell is strongest in the evening.

Smell is one of humanity's most important, and often overlooked, senses. It's intimately tied to taste and memory, and plays a pivotal role in detecting danger, whether from fires or rotten food. It may even play a role in how we choose our mates.

One little-known aspect of smell is how it fluctuates throughout the day. According to research conducted by Brown University and published in the journal Chemical Senses in 2017, our sense of smell is somewhat regulated by our circadian rhythm, the internal biological process that regulates a human's wake-sleep cycle. (If you've ever traveled across the ocean, the resulting jet lag is a disruption of this rhythm.)

The Brown study analyzed 37 teenagers for a week, and measured their sense of smell against their levels of the sleep-inducing hormone melatonin. A rise in melatonin meant that the body's nighttime circadian rhythm was kicking in, essentially saying, "It's time to sleep." The results showed that the teens' sense of smell was at its highest in the evening, around 9 p.m., or what the researchers called the beginning of "biological night." Conversely, their sense of smell was at its lowest between the hours of 3 a.m. and 9 a.m., when the body has little need for sniffing. Scientists can only guess at why the body kicks its olfactory receptors into high gear at 9 p.m. — it may help humans ensure satiety following the last meal of the day, scan for nearby threats before sleeping, or act as a means for encouraging that aforementioned mate choice.

Smell in humans begins declining after the age of 30.

FACT

FIB

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The animal with the strongest sense of smell is the __.

REVEAL ANSWER

		Numbers Don't Lie

Estimated percentage of people who are anosmic, meaning they have no sense of smell

Year the first modern perfume was created, for Queen Elizabeth of Hungary

1370

Estimated frequency (in days) at which human olfactory receptor cells are replaced

Years ago that olfactory receptors emerged in nature, in fishlike animals known as lancelets

550 million

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Humans are more sensitive than dogs when it comes to certain scents.

The human nose often takes a backseat to other famous sniffers in the animal kingdom. Dogs, pigs, and elephants have nasal biology jam-packed with olfactory receptors, which makes them particularly gifted at smelling scents. But no two odors are exactly alike, and research from Rutgers University argues that the human nose — with our measly 400 different kinds of olfactory receptors — can actually sniff out smells important to humans better than even the most skillful bloodhound. For example, human noses are more sensitive to amyl acetate, a main odorant found in bananas, because ripe fruit was important for our survival thousands of years ago. For dogs, finding such fruit was much less important, and thus biologically deprioritized. Human noses can also sniff out the smell of fresh rain on dirt, a scent known as "petrichor," better than a shark can smell blood in the sea, likely due to our essential need for fresh water. So don't write off your sense of smell — instead, take pride in what your nose knows.

Today's edition of Interesting Facts was written by Darren Orf and edited by Bess Lovejoy.