Well-known antigens that can cause anaphylaxis include penicillin, insect venom, pollen extracts, fish, shellfish and nuts. IgE antibodies attach themselves to mast cells and basophils, priming the body for the allergic reaction. The released mediators cause blood vessels to dilate and leak fluid into the surrounding tissues and cause smooth muscle in the airways to contract. Since the middle of the 20th century, penicillin has been by far the most common cause of anaphylaxis. Nevertheless, although many millions of people in the United States are allergic to insect venom, and hundreds of thousands of them have allergic reactions to stings each year, the number of deaths reported from these reactions is estimated at only 50 to 100 per year.
Dyes used in certain diagnostic X-ray tests are the most common cause.
The reason for mast cell degranulation in these circumstances is not thoroughly understood. Some people with exercise-induced anaphylaxis develop symptoms only if they've eaten before exercising. The patient's problem resolved when she ate dinner after dancing rather than before. There are numerous other less common precipitators of anaphylactic or anaphylactoid reactions. Researchers at Northwestern University Medical School in Chicago recently reported on 73 patients with idiopathic anaphylaxis.