Studies have shown that women tend to suffer more severe allergic reactions than men, and now researchers may have uncovered a clue as to why. A study out of the National Institute of Allergy and Infectious Diseases finds that in mice, estrogen "enhances the levels and activity" of an enzyme that causes allergic reactions, according to a press release. It has to do with what happens during anaphylaxis, a life-threatening allergic reaction that can be triggered by everything from peanut butter to a wasp sting. Here's how the body reacts: Immune cells release enzymes; the enzymes make tissue swell and blood vessels get wider. And as far as blood vessels go, the study found that estrogen boosts the activity of an enzyme that lines them; the result can be a drop in blood pressure and swelling.
In mice, the females experienced worse and longer-lasting anaphylaxis than the males, but when activity from that enzyme (endothelial nitric oxide synthase, or eNOS) was blocked, or when estrogen was blocked, female mice experienced anaphylaxis that was similar in severity to what the males experienced. More research needs to be done to see whether the same explanation applies to human allergic reactions, but researchers say certain women should take heed, the Washington Post reports. For example, a woman experiencing severe allergy problems should let her doctor know whether she's on birth control so any possible hormonal associations can be considered. (A mysterious allergic reaction took this 11-year-old girl's life.)