Anaphylaxis is a rare but severe allergic reaction. It occurs suddenly, can worsen quickly and can be deadly. Anaphylaxis happens after being exposed to a triggering agent. It can be caused by foods, insect stings, medication, and even plants. The agent leads to the release of normal body chemicals such as histamine that cause allergy symptoms. If the reaction is severe it is important to get an EPI pen to the person or seek emergency medical help immediately.