When a person is stung by a bee, wasp, hornet, yellowjacket or fire ants, the insect injects venom into its victim. This venom can cause severe life-threatening reactions in certain people who are allergic to it. In a typical reaction, the sting site will be painful, reddened, and may swell and itch, but this will only last a few hours. Enlarged local reactions might be seen with a painful swelling of several inches surrounding the area of the sting. This reaction might last for days.

In a severe allergic reaction the person might feel dizzy, nauseated and weak. Stomach cramps and diarrhea may occur. Generalized hives and itching, wheezing and difficulty breathing, and potentially an anaphylactic reaction with a sudden drop in blood pressure, loss of consciousness which may lead to death can occur if no immediate medical care is provided. In a majority of patients, venom immunotherapy will protect against any future life-threatening reactions. In the case of severe or generalized reactions, patients with known allergic sensitivities to insect venom should be evaluated by an allergist and placed on protective desensitization therapy.