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 it’s 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.