People who have an insect sting allergy suffer a stronger-than-normal reaction to insect stings due to an overreaction of their immune systems. Their immune systems produce antibodies (which in turn release histamines) in reaction to the insect's venom. Whereas most people experience little more than mild discomfort when stung by an insect, people with allergies to insect stings suffer a range of symptoms from redness and itching at the affected site to rashes and hives over their entire body. They also may sneeze, cough, and have trouble breathing.

In some cases, these people may suffer a dangerous allergic reaction called anaphylaxis. Symptoms of anaphylaxis are sudden lightheadedness, difficulty breathing, swelling in the throat, tightness in the chest, heart palpitations, and loss of consciousness. Anaphylactic shock  may result and can be fatal if not treated immediately.

Allergic reactions to the stings of insects such has honey bees, yellow jackets, hornets, wasps and fire ants can occur suddenly in people who have never before had an insect sting allergy. The condition is an acquired trait, and occurs due to sensitization from prior exposure.