Why mosquitoes find some of us more attractive than others

High school is volatile enough without introducing immortality, generation-spanning politics, and an endless thirst for blood, but that’s an ordinary day at Vampire Academy (now streaming on Peacock!). When and why a vampire decides to drink the blood of a specific person could have any number of complicated motivations, but if vampires are anything like our own real-world bloodsuckers, they might seek out some people more than others.

People have long speculated on what might attract or repel mosquitos. Some suggest that eating certain foods make you more or less attractive, while others think that sex or age contribute to how tasty mosquitos find you. It’s a question not just of comfort, but also of public health. Mosquito bites are annoying, but they can also be debilitating or deadly. According to a recent study published in the journal Cell, certain individuals can be more than a hundred times more attractive to mosquitos than others, and now we might know why.

Dr. Maria Elena De Obaldia led the study during their postdoctoral fellowship in the Laboratory of Neurogenetics and Behavior at Rockefeller University. They gathered scent data from scores of people over the course of years, and used those samples to identify what rings the mosquitos’ dinner bell. Capturing a person’s smell might seem like an impossible problem, but there was a relatively simple and obvious solution. If you’ve ever picked up a friend or family member’s shirt and caught a whiff of their signature scent, you’re already most of the way there. Scientists had study participants wear nylon stockings on their arms six hours a day for multiple days.

“This was something we asked people to do hundreds of times. The nylons could then be frozen so we could be flexible about when to use them. We would then take the nylons and cut them up into pieces about the size of an index card. That would then be placed in the behavioral assay and used as bait for mosquitos,” De Obaldia told SYFY WIRE.

Those samples had all identifying information removed, so researchers didn’t know who had worn a particular piece of nylon, but they could identify the samples by number. Pretty quickly, certain numbered samples started to stick out. Subject 33, for instance, was more than four times more attractive than the second most popular sample and more than 100 times more attractive than the least attractive sample. This suggests that something in our scent dictates, at least to some degree, how voraciously a mosquito will pursue a particular target.

“Once we understood which ones were the most or least attractive, we used the same method to collect odor to analyze chemically,” De Obaldia said. That chemical analysis revealed about 50 chemical compounds which appear to be a significant factor in how mouthwatering an individual is. Those samples which were highly attractive had higher levels of carboxylic acids than those who were less attractive.

“We think that’s an important part of this. We found that the people who were most attractive to mosquitos had much more of these acids on their nylons. We also had some clues because our lab and other labs have been able to make mutant mosquitos with defects in their sense of smell,” De Obaldia said.

Using CRISPR to edit the genome of mosquitos, researchers produced mutants incapable of sensing these acids and they were considerably compromised in their attraction to human odor. That confirmed that carboxylic acid is likely an important part of what makes you attractive to mosquitos, but it also revealed that the human-mosquito relationship is more complicated than we realize. While mutant mosquitos had a harder time detecting a potential blood meal than their unaltered counterparts, they were still able to distinguish between highly attractive and less attractive people.

To understand what’s happening here, we’ll imagine ourselves blindfolded while standing over a stove. In front of you, on the stove, are two pots. One is filled with a thin broth while the other is filled with a rich stew. Your sense of smell tells you definitively which is which, and you’re much more likely to gravitate toward the stew. Maybe even a hundred times more likely. Then your sense of smell is knocked out, not completely but pretty significantly. Maybe you’ve got a head cold or a sinus infection and you’re all blocked up. Your ability to detect either the broth or the stew is compromised. You’re not getting all of the signals you usually would. You might even be eating less because you’re having a hard time finding the kitchen without the smells to guide you. But you can still tell the difference between the broth and the stew, even if both have been dulled. That appears to be what’s happening with the mosquitos. We can successfully knock out some of their scent receptors but if you’re a mosquito magnet, they are coming for you.

At the moment, there’s little you can do about that. Over the course of the study, scientists observed that people who were mosquito magnets remained mosquito magnets. The levels of carboxylic acid production remained stable over long periods of time, suggesting it’s the result of something genetic or something in the skin microbiome. It’s unclear if there’s anything we can do to change those signals and turn someone super attractive to mosquitos into something of an insect schlub. That said, researchers are hopeful that continued investigation could reveal next generation mosquito repellents.

“We did find at least one person who, from their chemistry, looked like they should be a mosquito magnet but they were not. That shows that we clearly don’t understand everything. There may be multiple ways to be a mosquito magnet and there could be other compounds we haven’t identified yet which undo these super attractors. It would be really cool to understand why that one person was not a mosquito magnet,” De Obaldia said.