Medical Health Encyclopedia

Anaphylaxis

Injury Disease Nutrition Poison Symptoms Surgery Test Special Topic

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Shock Allergic reactions Anaphylaxis Hives Food allergies Insect stings and allergy Allergic reactions to medication Antibodies

Overview Symptoms Treatment Prevention

Anaphylaxis

Definition:

Anaphylaxis is a life-threatening type of allergic reaction.

Alternative Names:
Anaphylactic reaction; Anaphylactic shock; Shock - anaphylactic

Text Continues Below

---

Causes, incidence, and risk factors:

Anaphylaxis is an severe, whole-body allergic reaction. After an initial exposure to a substance like bee sting toxin, the person's immune system becomes sensitized to that allergen. On a subsequent exposure, an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body.

Tissues in different parts of the body release histamine and other substances. This causes constriction of the airways, resulting in wheezing, difficulty breathing, and gastrointestinal symptoms such as abdominal pain, cramps, vomiting, and diarrhea.

Histamine causes the blood vessels to dilate (which lowers blood pressure) and fluid to leak from the bloodstream into the tissues (which lowers the blood volume). These effects result in shock. Fluid can leak into the alveoli (air sacs) of the lungs, causing pulmonary edema.

Hives and angioedema (hives on the lips, eyelids, throat, and/or tongue) often occur. Angioedema may be severe enough to block the airway. Prolonged anaphylaxis can cause heart arrhythmias.

Some drugs (polymyxin, morphine, x-ray dye, and others) may cause an anaphylactoid reaction (anaphylactic-like reaction) on the first exposure. This is usually due to a toxic reaction, rather than the immune system mechanism that occurs with "true" anaphylaxis. The symptoms, risk for complications without treatment, and treatment are the same, however, for both types of reactions.