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This is why mosquitoes attract some people more than others.

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If you’ve always suspected you might be a mosquito magnet, scientists now have proof for you: Mosquitoes do indeed attract some people more than others, according to a new study.

A research team led by Leslie Vosshall, professor and head of the neurogenetics and behavioral laboratory at Rockefeller University, sought to determine why some people attract more mosquitoes than others. The research findings were published Oct. 18 in the journal Cell.

For three years, the researchers asked a group of 64 volunteers to wear nylon stockings on their arms for six hours a day for several days. Maria Elena De Obaldia, the study’s first author and former postdoctoral researcher at Rockefeller University, created a “two-option olfactometer test,” an acrylic glass chamber in which the researchers placed two socks. The study team then released yellow fever mosquitoes, scientifically called Aedes aegypti, into the room and observed which sock attracted more insects.

This test allowed the researchers to separate study participants into “mosquito magnets” whose socks attract large numbers of mosquitoes, and “low attractors” that don’t seem attractive to insects. The scientists examined the skin of mosquito magnets and found 50 molecular compounds in these participants that were higher than the others.

“We had no preconceptions about what we were going to find,” Vosshall, chief science officer at the Howard Hughes Medical Institute, told CNN. But one difference was particularly evident: Mosquito magnets had a much higher proportion of carboxylic acid in their skin than low attractors.

Carboxylic acids are found in sebum, the oily substance that creates a barrier and helps our skin stay hydrated.

Vosshall explained that carboxylic acids are large molecules. “They don’t smell that good on their own,” he said. But, according to Vosshall, beneficial bacteria on the skin “chew these acids that produce the characteristic odor of humans” – which may be what attracts mosquitoes.

Only one participant, identified as Subject 33, was the best of the ball for mosquitoes: Subject’s socks were 100 times more attractive to mosquitoes than the least attractive participants.

Vosshall said the level of people’s attraction remained fairly constant over time for participants tracked over the three-year period.

Subject 33, for example, “hasn’t stopped being the most attractive person for a day”, which might be “bad news for mosquito magnets.”

In the case of Aedes aegypti, female mosquitoes prefer to use human blood for egg production, which adds urgency to their hunt for humans to hunt. These mini-predators use a variety of mechanisms to identify and select the people they bite, Vosshall said.

Carboxylic acids are just one piece of the puzzle in explaining how pesky insects can choose their targets. Body heat and the carbon dioxide we release when we breathe also attract mosquitoes to humans.

Vosshall said scientists still don’t know why carboxylic acids attract mosquitoes so strongly. But the next step may be to explore the effects of reducing carboxylic acids on the skin.

“You can’t completely remove natural moisturizers from the skin, that would be bad for your skin health,” she said. But Vosshall said dermatological products can minimize carboxylic acid levels and reduce mosquito bites.

“Every bite of these mosquitoes puts humans at risk to public health,” he said. “Aedes aegypti mosquitoes are vectors for dengue, yellow fever and Zika. People with magnets will be much more likely to be infected.”

Matthew DeGennaro, an associate professor of mosquito neurogenetics at Florida International University, told CNN that the results of the study help answer longstanding questions about what specific factors are that cause mosquitoes to like some people more than others. He was not included in the study.

“This study clearly shows that these acids are important,” he said. “Now, it’s interesting how mosquitoes detect these carboxylic acids because these special chemicals are really heavy, so they’re hard to smell from afar.

“These chemicals could be being altered, say, by the skin microbiome, and this could cause a certain kind of odor cloud. Or it could be that other environmental factors degrade these chemicals a bit, making them easier for mosquitoes to detect.”

DeGennaro added that the results are also “a really great example of how well insects can smell.” “This insect evolved to prey on us.”

For DeGennaro, the persistence of some people’s attractiveness is one of the most interesting aspects of the research.

“We didn’t know that for some people, mosquitoes have such stable preferences,” he said. “While they don’t address that, it may suggest that the skin microbiome is important.”

Further research should investigate the microbiome that lives on human skin to understand why mosquitoes are attracted to certain compounds over others, he said. This could lead to better products for reducing mosquito bites and the spread of disease.

“If we understand why mosquitoes find a host, we can design new repellents that will prevent mosquitoes from detecting these chemicals,” DeGennaro said. “And this can be used to improve our current repellents.”