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Scientists and laypeople alike have long wondered why mosquitoes are more attracted to some people than others. Growing evidence suggests that a person's unique odor plays a large role in determining how alluring they are to the insects, with several odorants identified that act as mosquito attractants. Now, the sour scents of carboxylic acids can be added to that list, researchers at Rockefeller University reported yesterday (October 18) in Cell.

Omar Akbari, a cell and molecular biologist at the University of California, San Diego, who was not involved with the work, tells Scientific American that the study could help with formulating mosquito repellants in the future.

See “Malarial Mosquitoes Drawn to Human Smell

Anecdotally, many people will say that they are “mosquito magnets” as compared to others who rarely get bitten at all.

“The question of why some people are more attractive to mosquitoes than others—that’s the question that everybody asks you,” Leslie Vosshall, a study coauthor and neurobiologist at the Howard Hughes Medical Institute and the Rockefeller University, tells Scientific American. “My mother, my sister, people in the street, my colleagues—everybody wants to know.”

So Vosshall and her colleagues gathered 64 volunteers and asked each of them to wear nylon stockings around their arms for six hours to collect their unique skin odor. They then used these smell samples in a mosquito-attraction tournament: Placing two stockings into a separate traps side by side, they unleashed a swarm of female Aedes aegypti mosquitoes (the species that carries diseases such as dengue, yellow fever, and Zika) to see which stocking they gravitated toward. After pitting the different stockings against each other, the team came out with a winner that was about 100 times more attractive than the last place sample, The Guardian reports. The scientists repeated these experiments over three years with the same subjects, finding that the subject’s attractiveness rating remained stable over time despite fluctuations in diet or skin product usage.

“Mosquito magnets seem to remain mosquito magnets,” Matt DeGennaro, a neurogeneticist at Florida International University who was not involved with the research, tells The Guardian.

Citing previous research into the attractiveness of carboxylic acid, a molecule that is part of the skin’s moisturizing layer, the Rockefeller scientists performed a chemical analysis looking specifically at acidic compounds in the stocking samples. Sure enough, they found that the samples that were highly attractive to mosquitoes had high levels of carboxylic acids, especially long-chain fatty acids such as pentadecanoic, heptadecanoic, and nonadecanoic acids. “If you have high levels of this stuff on your skin, you’re going to be the one at the picnic getting all the bites,” says Vosshall.

The scientists tried genetically modifying the insects to reduce their sensitivity to the acids. However, this did not affect the mosquitoes’  preferences; they still overwhelmingly chose the nylons from mosquito magnets.

“I think this reflects [the fact] that mosquitoes are choosing who to bite based on several—potentially many—odors emanating from our skin,” Maria Elena De Obaldia, a study coauthor and neurogeneticist at Rockefeller University, tells New Scientist. “It also reflects redundancy in the olfactory system of the mosquito: when one receptor pathway is disrupted, the relevant molecules can still be detected by a different receptor pathway.”

See “The Neuroscience Behind Why Mosquitoes Always Find You

Unfortunately, it’s difficult to modify the production of carboxylic acids or other odorants without negatively impacting skin health, Vosshall tells The Guardian. And given the scientists’ genetic modification work, it is unlikely any single product could change a person’s skin odor to enable them to evade mosquitoes entirely.

“Mosquitoes are resilient,” she tells the newspaper. “They have many backup plans to be able to find us and bite us.”