Anaphylaxis can be caused by any allergen . However, the most common antigens to cause such a reaction are drugs , insect stings , certain food s and allergen immunotherapy injections. An anaphylactic reaction starts when the allergen enters the bloodstream and reacts with an IgE class antibody. The person may also go into shock . Anaphylaxis occurs immediately or at most within 2 hours of exposure to the allergen.
Treatment is an epinephrine injection, which usually stops the reaction.
Those who are allergic to bee stings or certain foods should carry a dose of epinephrine with them at all times.