Here’s 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: Mosquitoes are more attracted to some humans than others, according to a new study.

A research team led by Leslie Vosshall, a Rockefeller University professor and head of its neurogenetics and behavior lab, wanted to identify why some people seem to attract more mosquitoes than others. The findings of the study were published in the journal Cell on October 18.

Over the course of three years, the researchers asked a group of 64 volunteers to wear nylon stockings on their arms for six hours a day on several days. Maria Elena De Obaldia, the study’s first author and a former Rockefeller University postdoctoral fellow, constructed a “two-choice olfactometer test”—an acrylic glass chamber into which the researchers placed two pairs of socks. The research team then released yellow fever mosquitoes, scientifically known as Aedes aegypti, into the attic and saw which socks attracted more insects.

This test allowed the researchers to separate the study participants into “mosquito magnets,” whose socks attracted many mosquitoes, and “low attractors,” whose socks were not attractive to the insects. The scientists analyzed the skin of the mosquito magnets and found 50 molecular compounds in these participants than the others.

“We had no preconceptions about what we were going to find,” Vosshall, the Howard Hughes Medical Institute’s chief scientific officer, told CNN. But one difference was particularly distinctive: the mosquito magnets had much higher levels of carboxylic acids on their skin than the low attractants.

Carboxylic acids are found in sebum, an oily substance that forms a barrier and helps keep our skin moisturized.

Carboxylic acids are large molecules, Vosshall explained. “They’re not that smelly by themselves,” he said. But beneficial skin bacteria “chew up these acids, which creates the distinctive human odor”; that may be what attracts mosquitoes, according to Vosshall.

One participant, identified only as Subject 33, was the beauty of the mosquito ball: the subject’s socks were 100 times more attractive to mosquitoes than the least attractive participants.

And the level of human attraction seemed to remain relatively constant over time for the participants who were monitored over a three-year period, Vosshall said.

Subject 33, for example, “didn’t take a day off from being the most attractive human being,” which might be “bad news for mosquito magnets.”

As for Aedes aegypti, female mosquitoes prefer to use human blood to fuel their egg production, giving urgency to their search for human prey. And these small predators use a variety of mechanisms to identify and choose the humans they bite, Vosshall said.

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

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

“You can’t completely strip the skin of natural moisturizers, that would be bad for your skin’s health,” she said. However, Vosshall said dermatological products may be able to lower carboxylic acid levels and reduce mosquito bites.

“Every bite from these mosquitoes puts people at risk of public health,” he said. “Aedes aegypti mosquitoes are the vectors of dengue, yellow fever and Zika. Those people who are magnets will be much more likely to be infected with viruses.”

Matthew DeGennaro, an associate professor at Florida International University who specializes in mosquito neurogenetics, told CNN that the study’s results help answer long-standing questions about the specific factors that make mosquitoes love some humans more than others. He did not participate in the study.

“This study clearly shows that these acids are important,” he said. “Now, how mosquitoes perceive these carboxylic acids is interesting because these particular chemicals are very heavy, so they’re hard to smell from a distance.

“It could be that these chemicals are changing, let’s say the microbiome on the skin, and it’s causing a certain type of smell. Or it could be that other factors in the environment break down these chemicals a little, so mosquitoes can detect them more easily.’

The results are also “a great example of how good insects smell,” DeGennaro added. “This insect has evolved to hunt us.”

For DeGennaro, the enduring power of certain human attractiveness is one of the most interesting aspects of the study.

“We didn’t know that there were very stable mosquito preferences for some people,” he said. “It could suggest that the skin microbiome is important, although that hasn’t been addressed.”

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

“I think if we understand why mosquitoes find a host, we can design new repellents that will prevent mosquitoes from sensing these chemicals,” DeGennaro said. “And this could be used to improve our current rejections.”