Anaphylaxis is a serious life-threatening allergic reaction. Early symptoms of anaphylaxis may be mild, but they can quickly become more serious. If you have allergies, it's important to talk about them with your healthcare provider. He or she can help you understand if you're at risk for a severe reaction. If you are at risk, you will learn how to recognize and treat it. If you ever have one of these reactions, you will need treatment right away.