January 17, 2022

I, Science

The science magazine of Imperial College

John Bader
23rd October 2021

Have you ever heard of the phrase “I smell danger”? Well, while we keep using the phrase
figuratively, it turns out we can literally smell danger, study finds. 

A study carried out by researchers at the Karolinska Institute in Sweden finds that the scent-
detecting nerves in our nose start processing negative smells faster than positive ones. This,
in turn, leads to a more rapid response, which highlights a survival mechanism that we have
in common with other mammals. 

Assuming that negative smells are mostly indicative of a threat, rapidness of the response
becomes more of an essential inherent characteristic than an advantageous skill. In other
words, our instant jerk-away from the smell of rotten food, for instance, is not a voluntary
move, but rather a response that is triggered unconsciously. 

“The human avoidance response to unpleasant smells associated with danger has long
been seen as a conscious cognitive process, but our study shows for the first time that it’s
unconscious and extremely rapid,” says Behzad Iravani, one of the authors of the study. 

The results of the study are based on a series of experiments in which participants were
asked to rate their experience of various smells. The quality of the smell presented to the
participants was controlled using chemicals that are similar to odours that we are familiar
with; garlic, perfume, fruit, among other kinds of odours. In addition to the subjective “it
smells nice / it smells bad” question, the reactivity of the olfactory bulb (the part of the brain
responsible for smell) was measured using a non-invasive method called
electroencephalography, EEG for short.  

“It was clear that the [olfactory] bulb reacts specifically and rapidly to negative smells and
sends a direct signal to the motor cortex within about 300 ms,” explains Johan Lundström,
another author of the study. “The results suggest that our sense of smell is important to our
ability to detect dangers in our vicinity, and much of this ability is more unconscious than our
response to danger mediated by our senses of vision and hearing” he concludes by
suggesting that we can be more reliant on our sense of smell for survival.

Now knowing that your nose is smarter than you thought, you can confidently say with your

Iravani, B., Schaefer, M., Wilson, D. A., Arshamian, A., & Lundström, J. N. (2021). The human olfactory bulb processes odor valence representation and cues motor avoidance behavior. Proceedings of the National Academy of Sciences118(42).

John Bader is the News Editor for I,Science and is studying an MSc in Science Media Production at Imperial College London