After this weekend's barbeques and fireworks displays, you might wonder why some people wind up covered in mosquito welts and others are bite-free. It's not a coincidence. Each person's individual body chemistry determines how many mosquitoes will come calling.
According to Joe Conlon, a medical entomologist who advises the American Mosquito Control Association, the insects can detect their targets from nearly 100 feet away. But what are they seeking? Mostly the scent of carbon dioxide and lactic acid, two compounds that indicate to the hematophagous—or blood-sucking—pests that their next landing pad is nearby. (It's worth noting that when a female mosquito latches on to you, she's not looking for food; instead, she sucks out blood to help fertilize her eggs … that's why males don't "bite").
Carbon dioxide and lactic acid are released whenever we breathe or sweat, but the emission rates vary by person. Larger people and pregnant woman, for example, have higher levels and are more likely targets. According to Susan Peskewitz, a mosquito researcher and entomology professor at the University of Wisconsin-Madison, the scents of these compounds coupled with body heat are the biggest attractors. So if you've recently exercised, watch out: The combination of lactic acid (which builds up when muscles are exerted), sweat filled with carbon dioxide, and an increased temperature make you an ideal host.
With more than 300 bodily compounds that influence insect attraction, scientists haven't figured out every body chemistry combination that the bugs like. They're also not sure whether perfumes or floral smells affect attraction. But because mosquitoes drink dew, they may have a preference for artificially sweet-scented bodies. Some research has also shown they prefer landing on darker fabrics than light ones, so stay away from black or blue clothing and make sure your shirt isn't too tight; if it is, the insects will siphon right through it.
In the end, you can't change your body chemistry. But you can wear one of four Centers for Disease Control-approved repellents. Sprays and lotions including DEET, Picaridin, Oil of Lemon Eucalyptus or IR3535 (which has made Avon's Skin-so-Soft lotion a popular choice) have all been deemed effective and safe to keep the bugs at bay. But don't apply them near your eyes, ears, nose and mouth, or you'll have much more than itchy mosquito bites to worry about.