Anaphylaxis is a life-threatening type of allergic reaction.

Anaphylaxis is an severe, whole-body allergic reaction. After being exposed to a substance like bee sting venom, the person's immune system becomes sensitized to that allergen. On a later exposure, an allergic reaction may occur. This reaction is sudden, severe, and involves the whole body.

Tissues in different parts of the body release histamine and other substances. This causes the airways to tighten and leads to other symptoms.

Some drugs (polymyxin, morphine, x-ray dye, and others) may cause an anaphylactic-like reaction (anaphylactoid reaction) when people are first exposed to them. This is usually due to a toxic reaction, rather than the immune system response that occurs with "true" anaphylaxis.

The symptoms, risk for complications without treatment, and treatment are the same, however, for both types of reactions.

Anaphylaxis can occur in response to any allergen. Common causes include:

• Drug allergies
• Food allergies
• Insect bites/stings

Pollens and other inhaled allergens rarely cause anaphylaxis. Some people have an anaphylactic reaction with no known cause.

Anaphylaxis rarely occurs. However, it is life-threatening and can occur at any time. Risks include history of any type of allergic reaction.