Why I Don't Get Bit By Mosquitos

John

Nov 29

I grew up in Florida. It's pretty much the mosquito capital given all the water and year round climate. Other places can be more intense, but for being bit all year long, it's hard to beat the Sunshine State.

I got bit as a kid as much as others. Heck, we vacationed in a place that has a section of the city called Mosquito Lagoon. It's some of the best Red Fishing outside of Louisiana.

We didn't have air conditioning at first when I was young so the window were open. Ever been kept away by the whine of a buzzing biter in your ear. Yes, just like the dentist drill we all know the noise.

I began to notice in my 20's though that others were getting bit more than me. There were also biting gnats (no see'ums) that were almost worse. You couldn't see them. You could at least kill some mosquitos if you saw them in time.

I thought that maybe I got anti-bite serum from being bit so much. Then I remembered that as kids, we used to follow the mosquito truck on our bikes in the smoke breathing in what has to be DDT or worse. I figured I had natural immunity.

My dad didn't get bit much either. As a joke, he said it was the meanness in him that kept them away.

It turns out that some people just get bit more and I'm not one of them.

SOME PEOPLE ARE MOSQUITO MAGNETS

As you may have noticed, mosquitoes don't attack everyone equally. Scientists have known that the pests are drawn to people at varying rates, but they have struggled to explain what makes certain people "mosquito magnets" while others get off bite-free.

In a new paper published on October 18 in the journal Cell, researchers suggest that certain body odors are the deciding factor. Every person has a unique scent profile made up of different chemical compounds, and the researchers found that mosquitoes were most drawn to people whose skin produces high levels of carboxylic acids. Additionally, the researchers found that peoples' attractiveness to mosquitoes remained steady over time, regardless of changes in diet or grooming habits.

"The question of why some people are more attractive to mosquitoes than others—that's the question that everybody asks you," says study co-author Leslie Vosshall, a neurobiologist and mosquito expert at the Howard Hughes Medical Institute and the Rockefeller University. "My mother, my sister, people in the street, my colleagues—everybody wants to know." That public interest is what drove Vosshall and her colleagues to design this study, she says.

Scientists have put forth some theories to explain why mosquitoes swarm to some of us more than others, including one idea that differences in blood type must be to blame. Evidence is weak for this link, however, Vosshall says. Over time, researchers began to coalesce around the theory that body odor must be a primary culprit in mosquito attraction. But scientists have been unable to confirm which specific odors mosquitoes prefer.

To answer this question, Vosshall and her colleagues gathered 64 participants and had them wear nylon stockings on their arms. After six hours, the nylons were imbued with each person's unique smell. "Those nylons would not have a smell to me or, I think, to anyone really," says Maria Elena De Obaldia, a senior scientist at the biotech company Kingdom Supercultures and lead author of this new study, which she conducted while at Rockefeller. Still, the stockings were certainly odorous enough to entice mosquitoes.

The researchers cut the nylons into pieces and placed two (from different participants) into a closed container housing female Aedes aegypti mosquitoes. Did they migrate to subject number one's sample en masse or prefer the scent of subject number two's? Or were both equally appealing? The researchers continued these head-to-head battles over several months, Vosshall says, collecting new samples from the participants as needed. When the tournament was over, the team had clear proof that some people were more attractive than others. Subject 33 had the dubious honor of being the biggest mosquito magnet; they had an attractiveness score "over 100 times greater" than that of the least attractive subjects, 19 and 28, the study authors wrote.

The researchers analyzed the subjects' scent profiles to see what might account for this vast difference. They found a pattern: the most attractive subjects tended to produce greater levels of carboxylic acids from their skin while the least attractive subjects produced much less.

Carboxylic acids are commonplace organic compounds. Humans produce them in our sebum, which is the oily layer that coats our skin; there, the acids help to keep our skin moisturized and protected, Vosshall says. Humans release carboxylic acids at much higher levels than most animals, De Obaldia adds, though the amount varies from person to person. The new study had too few participants to say what personal characteristics make someone more likely to produce high levels of carboxylic acids—and there's no easy way to test your own skin's carboxylic acid levels outside of the laboratory, Vosshall says. (She muses, however, that sending people skin swabs in the mail could make for an interesting citizen science project in the future.)

"This property of being a mosquito magnet sticks with you for your whole life—which is either good news or bad news, depending on who you are," Vosshall says.

"This study confirms, in a very careful way, that it is 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 with the study but whose recent work focuses on mosquitoes. He adds that the study's identification of specific carboxylic acids as a key determinant of mosquito attraction is a new contribution to biologists' understanding of the insects' behavior. Akbari suspects that the results of this study—which focused on A. aegypti mosquitoes—are probably generalizable to other species of mosquitoes that also primarily prey on humans.

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