Why do some people react more to bug bites?


Why do some people react to bug bites and others don’t? —Kate-Lynn Rich, Sylvan Lake, Alta.

It has to do with individual differences in our immune systems, says Tim Geary, director of the Institute of Parasitology at McGill University. Biology time: The immune system is your body’s defence system. When under attack from, say, a mosquito bite, it releases histamine (and other inflammatory substances) to the site of the bite, in reaction to the foreign enzymes in the saliva of the mosquito. The more histamine that is released, the more that spot swells—and itches.

Strangely, some people react dramatically to only one insect—mosquitoes or fleas, for example—or to several insects, or to all of them. Or to none of them.

“I don’t react to bites,” says Geary. “You can’t even tell I’ve been bitten.”

Well, that’s nice for him. But what causes these (unfair) immune system differences? Nobody knows. “Whether or not you react to a mosquito is not considered life-threatening,” says Geary. So, compared to, say, mosquito-borne illness, it hasn’t been studied much.

Plus, while it’s common to test for allergies to stinging insects (such as bees), allergy tests for biting insects (such as mosquitoes) are not standardized, explains Susan Waserman, an allergist and clinical immunologist at McMaster University’s department of medicine. Other diagnostic allergy tests use insect venom, but there is no good skin-test reagent developed to test for mosquito allergy. The only option is to test someone’s reaction to a “whole-body extract”—from, literally, a crushed mosquito—which isn’t as precise and makes diagnosis difficult.

Luckily, mosquito bites are rarely associated with any significant allergy or anaphylaxis, says Waserman. “It’s possible. It’s just not common.”