Smells Change Depending on Stress Levels: How Anxiety Influences Our Senses

Smell is one of the oldest of the senses in evolutionary terms. Animals that range from invertebrates to humans use this sense in order to navigate the world. Now, scientists have discovered that smells may change depending on our stress levels; it turns out that when we're anxious, neutral orders can turn distasteful.

Scientists have long known that smells are tied to the brain. They can stir emotions, bring up memories and exert their influence biologically. Yet exactly how this happens has long been a mystery to researchers. In order to better understand the science of smell, though, scientists employed new brain imaging technologies.

In this case, the researchers used functional magnetic resonance imaging (FMRI) in addition to behavioral techniques as they examined the brains of a dozen human participants. As they scanned the volunteers' brains, the researchers showed them anxiety-inducing pictures and text of things like car crashes and war. At the same time, the scientists exposed them to known neutral odors.

"After anxiety induction, neutral smells become clearly negative," said Wen Li, one of the researchers, in a news release. "People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odors. It becomes more negative as anxiety increases."

So what did they find? It turned out that two distinct and typically independent circuits of the brain-one dedicated to olfactory process and the other dedicated to emotion-become intimately intertwined under conditions of anxiety. This means that whether or not a person was stress changed the way they perceived certain smells.

"In typical odor processing, it is usually just the olfactory system that gets activated," said Li. "But when a person becomes anxious, the emotional system becomes part of the olfactory processing system."

The findings aren't just important for understanding how we perceive smells, though. They also may have clinical implications in the sense that they begin to undercover the biological mechanisms at play during periods of anxiety.

"We encounter anxiety and as a result we experience the world more negatively," said Li. "The environment smells bad in the context of anxiety. It can become a vicious cycle, making one more susceptible to a clinical state of anxiety as the effects accumulate."

The findings are published in the Journal of Neuroscience.