Disgusting odors trigger the body’s defense against infections

(ORDO NEWS) — Researchers from several countries at once found evidence that the feeling of disgust is associated with an increase in the body’s immune defenses.

That is, thanks to the sense of smell, we not only avoid unpleasant things and their smells, but even at the cellular level we prepare for a possible attack by pathogens.

In the course of evolution, animals, including humans, have developed special reactions that protect against poisoning and disease. Aversion to certain smells is one such evolutionary defense.

Scientists even gave such reactions a name – the behavioral immune system.

Researchers from several countries have wondered if our main immune system is responding to such “wake-up calls” from our sense of smell.

This would be logical: the body feels the presence of a potential danger, which means it must prepare for problems in advance.

Scientists from Sweden and Australia, Germany and the United States conducted three independent experiments to find out if this is really the case.

The scientists used three methods to induce strong disgust in the subjects.

Swedish researchers gave volunteers smells of unpleasant odors: fermented herring, blue cheese, rotten yeast, artificial fragrances with the smell of urine and sweat.

Participants rated each smell on a “disgusting scale,” and then scientists collected saliva samples from people who smelled the most unpleasant odors.

As a result, in the saliva of the participants who experienced the strongest disgust, the researchers found elevated levels of two immune markers: tumor necrosis factor TNF-α and secretory immunoglobulin S-IgA.

TNF-α activates several types of immune cells in the body, including cytokines and white blood cells. This is an important factor in protecting the body from intracellular parasites and viruses.

Secretory immunoglobulin A is one of the most important antibodies, cells that neutralize foreign substances. By the way, this type of immune cells was of interest to scientists in all three studies.

The work of the Swedish and Australian scientists was published in the scientific journal Evolution, Medicine, and Public Health on December 15, 2022.

The German scientists disgusted the volunteers in a very different way.

Participants in the study were shown videos with repulsive scenes of various kinds. Some were shown situations of possible infection with pathogens (people sneezing and coughing directly into the camera), others were shown disgusting images of decomposing animal corpses, as well as cockroaches.

Of course, there was also a control group in the study – the lucky ones from this group looked at the peaceful landscapes.

In the saliva of participants who were shown videos of visually ill people, and participants who observed scenes of unsanitary conditions, the level of S-IgA increased.

Curiously, the concentration of immunoglobulin was somewhat lower in those who experienced the most disgust.

It seems that behavioral immunity can compensate for natural immunity in this way: a person with a strong disgust is unlikely to come close to a potential “infection”, therefore, most likely, he will not have to fight pathogens.

Finally, the American scientists used both smells and videos in their study to disgust the participants. In the end, they found that unpleasant odors were much more effective than repulsive videos.

They also found that people who experienced disgust had increased levels of S-IgA in their saliva.


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