Photo: Elizaveta Galitckaia (Shutterstock)

Have you ever gone on a group hike where you all forgot to bring bug repellent, or perhaps held a backyard barbecue where the mosquitoes came out in force? Chances are, by the end of the day, some people are covered in bites while others have just one or two itchy spots. “Mosquitoes love me,” the unfortunate among you might remark. And it’s probably true.

We’ve known for a long time that mosquitoes seem to prefer some people to others, but sussing out the reasons why has been difficult. Spoiler: While scientists haven’t cracked this mystery quite yet, we have a bunch of clues.

Body size and activity

For starters, we know that mosquitoes navigate toward us by smelling carbon dioxide, which we constantly exhale. The bigger you are, the more oxygen you breathe in and the more carbon dioxide you breathe out. This means adults are more easily found by mosquitoes than children, bigger adults are more easily found than smaller adults, and you’ll be an easier target for mosquitoes when you’re pregnant than when you’re not.

We also breathe more when we exercise, because we need more oxygen to burn the calories that fuel that exercise. That results in more carbon dioxide. So when you’re exercising, you’re more of a target than when you’re sitting still. Mosquitoes also detect the warmth of our bodies, which exercise increases with exercise as well.

Dark clothing

Once mosquitoes have located our general area, they fly toward large, dark objects. People wearing dark clothing get more mosquito bites than those wearing light clothing. So when the mosquitoes are out, consider dressing in light colors. Some research suggests red or orange clothing is especially attractive to Aedes mosquitoes (the stripey ones you find in southern parts of the U.S.) so you may want to stick to blues and greens when you’re choosing your pastel wardrobe.

Just the way you smell

There are definitely other factors that influence who the mosquitoes like, but scientists are still working on figuring out what they are. Drinking alcohol seems to have an effect on how attractive we are to the insects, for one.

But there’s more. In one recent study, researchers asked people to wear stockings on their arms for several days to soak up their scent, and then exposed these stockings to mosquitoes. The skeeters preferred some of the stockings to others, which wasn’t surprising; the scientists’ plan was to genetically alter mosquitoes’ sense of smell and see if this stopped them from smelling some people or all people. That aspect of the experiment didn’t work out.

But in the process, it turned out that the differences from person to person weren’t subtle. One sample, from Subject 33, was 100 times as attractive to the mosquitoes as the least-attractive sample. As the researchers told Sci Tech Daily:

The samples in the trials were de-identified, so the experimenters didn’t know which participant had worn which nylon. Still, they would notice that something unusual was afoot in any trial involving Subject 33, because insects would swarm toward that sample. “It would be obvious within a few seconds of starting the assay,” says [researcher Maria Elena] De Obaldia.

Chemical analysis showed that the more attractive stockings were high in carboxylic acids, a family of chemicals we make in our sebaceous glands. The bacteria and other microbes that grow on our skin probably influence this chemical profile, as well (and perhaps vice versa). So we’re still learning whysome people smell better to mosquitoes, but at least it’s clear that the difference is real.