Anaphylactic, an uh fu LAK tihk, shock, also called anaphylaxis, is a rare, life-threatening allergic reaction that affects the whole body. The reaction develops rapidly after two or more exposures to an allergen (substance that causes an allergy). The allergens that cause most anaphylactic reactions include bee and wasp venom, antibiotics, latex rubber, and such foods as eggs, nuts, and shellfish.