As you may have noticed, mosquitoes don’t all attack the same way. Scientists knew that parasites are attracted to people to varying degrees, but they have struggled to explain what makes some people “mosquito magnets” while others get away with no bites.
In a work published in the journal Cell, a group of researchers suggests that certain body odors are the deciding factor. Each person has a unique olfactory profile made up of different chemical compounds, and researchers have found that mosquitoes are more attracted to people whose skin produces high levels of carboxylic acids. Furthermore, the researchers found that people’s attractiveness to mosquitoes remained constant over time, regardless of changes in diet or personal hygiene habits.
“The question of why some people are more attractive to mosquitoes than others is a question everyone asks,” says study co-author Leslie Vosshall, a neurobiologist and mosquito expert at Rockefeller University. “My mother, my sister, the people on the street, my colleagues: everyone wants to know”. This public interest is what prompted Vosshall and his colleagues to design this study.
Are you a mosquito magnet?
Scientists have put forward some theories as to why mosquitoes swarm some of us more than others, including the idea that differences in blood type are to blame. However, according to Vosshall, the evidence to support this link is scant. Over time, researchers have begun to converge on the theory that body odor must be primarily responsible for mosquito attraction. But the researchers were unable to confirm which specific smells are favored by mosquitoes.
To answer this question, Vosshall and his colleagues gathered 64 participants and had them wear nylon stockings on their arms. After six hours, the nylons were impregnated with each person’s unique smell. “Those nylon stockings wouldn’t have smelled for me or, I think, for anyone else,” says Maria Elena De Obaldia, researcher senior from biotech firm Kingdom Supercultures and lead author of this new study, which she carried out while at Rockefeller. However, the socks were certainly smelly enough to attract mosquitoes.
How to make mosquitoes insensitive to our smell
The researchers cut the nylons into pieces and placed two (from different participants) in a closed container that housed mosquitoes. Temples of the Egyptians females. Did the mosquitoes migrate en masse to the sample of subject number one or did they prefer the smell of that of subject number two? Or were they both equally attractive? The researchers continued these head-to-head comparisons for several months, Vosshall explains, collecting new samples from participants as needed. By the end of the trial, the group had clear evidence that some people were more attractive than others. Subject 33 had the dubious honor of being the largest mosquito magnet; he had an attractiveness score “over 100 times higher” than the least attractive subjects, 19 and 28, the study authors write.
The researchers analyzed the subjects’ olfactory profiles to understand what could explain this great difference. They found a pattern: the more attractive subjects tended to produce higher levels of carboxylic acids from their skin, while the less attractive subjects produced far less.
Carboxylic acids are common organic compounds. Humans produce them in the sebum, which is the oily layer that covers the skin; here the acids help keep the skin hydrated and protected, explains Vosshall. Humans release carboxylic acids at much higher levels than most animals, adds De Obaldia, although the amount varies from person to person. The new study had few participants to say what personal characteristics make a person more likely to produce high levels of carboxylic acids, and there’s no easy way to test one’s skin’s carboxylic acid levels outside the lab, says Vosshall. . However, the researcher speculates that sending skin swabs by post could be an interesting project in the future citizen science.
However, we do know that the skin maintains a relatively constant level of carboxylic acids over time. This, in turn, leads to a consistent odor profile. (Mosquitoes may also be attracted to skin bacteria that digest the carboxylic acids we make, suggests Vosshall.) When Vosshall and De Obaldia repeated the experiment several times, several months later, they found that people’s attractiveness rankings remained mostly unchanged. All the personal factors that might have changed over the course of those months, from what each subject ate to the type of soap he used, didn’t seem to make a difference.
The neurons of mosquitoes dedicated to the taste of blood
“This property of being a mosquito magnet remains for life, which is good or bad news, depending on who you are,” says Vosshall.
“This study confirms, very accurately, that it’s true that some people are more attractive to mosquitoes than others,” says Omar Akbari, a cell and molecular biologist at the University of California, San Diego, who was not involved in the study but whose recent work has focused on mosquitoes. He adds that the identification of specific carboxylic acids as determinants of mosquito attraction is a new contribution to biologists’ understanding of insect behavior. Akbari suspects the results of this study – which focused on mosquitoes A. aegypti – are probably generalizable to other mosquito species that mainly prey on humans.
But if you think you are a mosquito magnet, not all hope is lost. Akbari says the study could help researchers develop more effective mosquito repellants in the future. The secret may lie in adding new bacteria to the skin’s existing microbiome to change its olfactory profile.
Akbari is working on a U.S. Department of Defense-funded project called ReVector that seeks to develop repellents that can be applied once and remain active for several months. “The idea is to take the skin bacteria that colonize humans … and to engineer them so that they can express a repellent compound or be able to degrade something attractive,” Akbari explains. Now that Vosshall and De Obaldia’s team have identified specific carboxylic acids that could be potent attractors, researchers could look to design bacteria-based skin creams that are specifically targeted at breaking down these compounds, Akbari points out.
However, one question remains: why do mosquitoes love the smell of carboxylic acids or accompanying bacteria so much? De Obaldia has an answer, but it’s a bit speculative, she admits. The author notes that mosquitoes A. aegypti they evolved to specifically prey on humans (perhaps because we often have clean water containers nearby, a perfect place for them to breed). Therefore, A. aegypti she has become extremely adept at distinguishing the smell of humans from that of other animals. Carboxylic acids are compounds that humans emit in abundance, while other animals do not. So, according to De Obaldia, mosquitoes have likely learned to love carboxylic acids because they are a great indicator that insects have spotted a human.
If you find yourself covered in bites more than any of your friends, you can console yourself by thinking that mosquitoes love your olfactory profile because it is so distinctly human.
(The original of this article was published in “Scientific American” on October 18, 2022. Translation and editing by Le Scienze. Reproduction authorized, all rights reserved.)