For most people, being stung by a bee, wasp, or hornet is annoying and maybe a little painful, but it is not a life or death situation. However, if you have an allergy to one of these insects, one sting can potentially be serious—the venom can cause a life-threatening allergic reaction called anaphylaxis.

A normal reaction to being stung by a bee, wasp, or hornet includes itching, redness, and swelling at the site of the sting. Most people get better within a couple of hours or days, but those who have an allergy to the insect that stings them may experience more severe reactions to being stung.

When an insect stings you, they inject a toxic substance called venom. If you’re allergic, your immune system views the venom injected as a harmful invader and responds by releasing a chemical called histamine. The release of histamine and other chemicals is what causes your reaction.