How do you know if you have a tough mosquito? You slap him and he slaps you back.

You're flipping burgers for the neighborhood barbecue, and the mosquitoes have already begun their feast -- on you. As you swat madly at the pests, you notice other folks seem completely unfazed. Could it be that mosquitoes prefer dining on some humans over others? This may clear up the mystery.

It's true. Mosquitoes do exhibit blood-sucking preferences, say the experts. "One in 10 people are highly attractive to mosquitoes," reports Jerry Butler, PhD, professor emeritus at the University of Florida. Incidentally, it's not dinner they're sucking out of you. Female mosquitoes -- males do not bite people -- need human blood to develop fertile eggs. And apparently, not just anyone's.

"People with high concentrations of steroids or cholesterol on their skin surface attract mosquitoes," Butler tells WebMD. That doesn't necessarily mean that mosquitoes prey on people with higher overall levels of cholesterol, Butler explains. These people simply may be more efficient at processing cholesterol, the byproducts of which remain on the skin's surface.

Mosquitoes also target people who produce excess amounts of certain acids, such as uric acid, explains entomologist John Edman, PhD, spokesman for the Entomological Society of America. These substances can trigger mosquitoes' sense of smell, luring them to land on unsuspecting victims.

"Any type of carbon dioxide is attractive, even over a long distance," Conlon says. Larger people tend to give off more carbon dioxide, which is why mosquitoes typically prefer munching on adults to small children. Pregnant women are also at increased risk, as they produce a greater-than-normal amount of exhaled carbon dioxide. Movement and heat also attract mosquitoes.

Are You A Mosquito Magnet? [WebMD]