Understanding Anaphylaxis - the Basics

What Is Anaphylaxis?

Anaphylaxis is a sudden, severe allergic reaction that occurs when you are exposed to a substance that your body was sensitized to during a previous exposure.  You cannot have an anaphylactic reaction to a substance the first time you are exposed to it.  Instead, during your first exposure to a substance, your body may produce antibodies.  Then when you are exposed to the substance again, your antibodies may react with the substance, or allergen, resulting in anaphylaxis.  However, you may not realize that you were exposed before to the offending allergen.

The reaction causes a sudden release of chemicals, including histamines, from cells in the blood and the body's tissues. These chemicals dilate the blood vessels, lowering blood pressure, and they cause the blood vessels to leak fluid, leading to hives and swelling, especially around the face and throat. The chemicals also act on the lungs, causing an asthmatic reaction -- that is, causing the lung's airways to constrict, thus making breathing very difficult.

In some cases, anaphylaxis is mild, causing only hives and itching. But it can be deadly. In anaphylactic shock, the most severe form of anaphylaxis, blood pressure drops severely; water rapidly leaves the blood stream, causing severe swelling; and bronchial tissues swell dramatically. This causes the person to choke and collapse. Anaphylactic shock is fatal if not treated immediately.

What Causes It?

Theoretically, almost any substance can provoke an extreme allergic response.

However, the most common causes of anaphylactic shock are:

• Peanuts
• Tree nuts; particularly almond, walnut, hazel, Brazil, and cashew nuts
• Shellfish, especially shrimp and lobster
• Dairy products
• Egg whites
• Wasp or bee stings
• Sesame seeds

Less common causes include:

• Fish
• Latex
• Penicillin or any drug or injection.
• Muscle relaxants
• Alcohol
• Exercise, after consumption of an allergy-provoking food.

Anaphylaxis occurs usually within minutes of exposure to the allergen and almost always within two hours. The most severe cases may be fatal just 10 minutes after exposure. If administered in time, an injection of epinephrine (adrenaline) may reverse the condition by quickly constricting blood vessels, increasing the heart rate, stopping swelling around the face and throat, and relaxing smooth muscles in the lungs. Because anaphylaxis can progress so quickly, the first signs of reaction should be taken seriously. Do not wait to see how serious the reaction may become: call for emergency help immediately (call 911 in the United States). Immediate treatment can help ensure full recovery.