Almost any substance can trigger an anaphylactic reaction, but the most common offending agents are foods, drugs and insect stings. Less common triggers are latex and exercise. In the United States penicillin is the most common culprit among antibiotics, resulting in anaphylactic death in 100 cases per year. Insect stings from honeybees, wasps, yellow jackets, hornets and fire ants account for an estimated 40 deaths per year.
There are individuals who will experience anaphylaxis without an obvious cause. This is called idiopathic anaphylaxis. Upon more intense investigation the doctor may uncover a substance of mechanism responsible for these reactions. Recently, it has been appreciated that in addition to a single exposure, like a particular food or drug, a combination of events can produce an anaphylactic reaction. For example, a patient develops hives and abdominal pain during exercises soon after eating peanuts. The patient has no difficulty on other occasions when he exercises or eats peanuts, just the combination of these two leads to trouble.
Anaphylaxis is a medical emergency requiring immediate treatment. For a mild case of itchy hives, an antihistamine (for example Benadryl) will do just fine. However, antihistamines will not treat an anaphylactic reaction. Anaphylaxis requires epinephrine (adrenaline) for immediate relief and often steroids to prevent a recurrence over the next few days.
Epinephrine works directly on the respiratory and cardiovascular systems to counteract the rapidly constricting muscles surrounding the bronchial tubes, wide open blood vessels that cause a drop in blood pressure, and swelling of the skin. Epinephrine is available in easy to use self-injecting devices (Epi-pen or Auvi-Q). These should be used if there are signs of a severe, life threatening reaction and you should head for the nearest emergency room in the event the reaction overcomes the positive effects of epinephrine. This drug accelerates heart rate (potentially dangerous in patients with heart disease) and only should be used when medically necessary.
Once you have recovered from an anaphylactic attack it is important to attempt to identify the cause so future episodes can be avoided. With the help of your doctor an exposure can often be determined by a review of your activity preceding the attack. Allergy testing is available for some of the substances capable of precipitating anaphylaxis. While there is no magic pill or shot to prevent future reactions, patients can be desensitized to insect stings and some drugs. Desensitization works by taking small amounts of the allergic substance in gradually increasing amounts until your body becomes accustomed to it.