Researchers at Karolinska Institutet have discovered that our sense of smell helps us detect and respond to threats. Being able to smell danger improves our chances of survival. For example, if you smell toxic fumes or rotting food, your instincts probably tell you to run.

Naturally, we want to avoid unpleasant odors because they may lead to fatal consequences. On the contrary, we seek out pleasant smells since our brain associates them with a possible reward.

The team used an innovative technique to determine what happens in the brain when we smell danger. The study, published in the journal PNAS, indicates that we process unpleasant smells much faster than positive smells. This response probably occurs so we can respond quickly to any perceived threats. Unsurprisingly, negative aromas trigger a physical avoidance response when the brain signals to the nervous system.

“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 the study’s first author Behzad Iravani, a researcher at the Department of Clinical Neuroscience, Karolinska Institutet.

The olfactory organ comprises about 5% of the human brain, allowing us to differentiate between millions of smells. Many of these smells can threaten our health and survival, such as chemicals or spoiled food. The brain processes odor signals in just 100 to 150 milliseconds after a smell passes through our nose.

Every living being on Earth depends on survival instincts, such as avoiding danger and seeking rewards. For humans, the sense of smell plays a crucial role in identifying and responding to potential threats. Scientists have long wondered how our brains process unpleasant odors and signal us to avoid them.

Researchers Learn How the Sense of Smell Warns Us of Threats

sense of smell
Because no non-invasive methods to measure signals from the olfactory bulb existed previously, it’s been challenging to study. The olfactory bulb represents the first part of the rhinencephalon (aka “nose brain”) with direct connections to essential components of the central nervous system. When signals from the brain travel to this area, our nervous system helps us identify and recall dangerous situations or substances.

For the study, researchers developed a technique to measure signals from the human olfactory bulb for the first time. This part of the brain processes odors and sends signals to the motor cortex and amygdala, which govern movement and avoidance behavior.

Results of the study come from three separate experiments where participants rated their experience of six smells. The researchers included both positive and negative smells in the experiment. They measured the electrophysiological activity of the participants’ olfactory bulbs during their experiences.

What the experts say:

“It was clear that the bulb reacts specifically and rapidly to negative smells and sends a direct signal to the motor cortex within about 300 ms,” says the study’s last author Johan Lundström, associate professor at the Department of Clinical Neuroscience, Karolinska Institutet. “The signal causes the person to unconsciously lean back and away from the source of the smell.”

He added: “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.”

The Knut and Alice Wallenberg Foundation, the National Institute on Deafness and Other Communication Disorders, and the Swedish Research Council funded the study. There are no reported conflicts of interest.

It’s fascinating that even though we live in modern environments, we retain many of our survival instincts. We no longer have to run from bears or lions, but our daily lives still present many challenges. Being able to navigate them using our sense of smell, in some cases, might just come in handy.

Four ways to add pleasant aromas to your home

If you want to make your living space more aromatic, we have a few tips. Luckily, most of them cost very little and can add pleasant smells to your environment.

  • Burn candles or incense. You can choose from probably thousands of different scents to cleanse your home of foul odors. From vanilla to sea breeze to holiday scents like snickerdoodle, you’re sure to find something you like. Alternatively, if you don’t want to inhale smoke from candles, you can opt for wax or oil burners. You can still enjoy various aromas without dealing with byproducts from fire.
  • Clean your living space. We know it’s not the most fun activity in the world, but it feels better to have a clean home. Make sure to regularly mop the floors, scrub toilets and bathtubs, and wash dishes before they pile up. This diligence will help eliminate any unpleasant smells while keeping your home fresh and spotless.
  • Keep dirty shoes in the garage. In many Asian countries, it’s customary to leave shoes outside the home or in the foyer. This custom keeps any dirt, bugs, or outside elements from contaminating the living area. In the house, wear slippers or house shoes instead for a cleaner environment. Your sense of smell will thank you because shoes can get pretty stinky after a while.
  • Deep clean and vacuum your carpets. Especially if you have pets, it’s essential to clean your carpets often. If you don’t, you’ll still want to give the carpets some TLC with baking soda and a thorough vacuum. Many people tout baking soda as the ultimate odor killer – plus, you can use it on multiple surfaces.

sense of smell
Final thoughts on how scientists better understand how our sense of smell alerts us to danger

A new study by scientists from Karolinska Institutet in Sweden reveals that our sense of smell serves as an early warning system. When we smell something unpleasant, our brain immediately signals our nervous system, triggering an avoidance response. This response helps us react quickly to dangers and increases our chances of survival.

Our sense of smell helps us in various situations. It may cause us to throw out rotting food instead of eating it or run from smoke in the distance. We still have our survival instincts, but we use them quite differently than in the past.