Basic facts

What is anaphylaxis?

Anaphylaxis is an extreme and severe allergic reaction. The whole body is affected, often within minutes of exposure to the allergen but sometimes after hours.

What can cause anaphylaxis?

Common causes include foods such as peanuts, tree nuts (e.g. almonds, walnuts, cashews, Brazils), sesame, fish, shellfish, dairy products and eggs. Non-food causes include wasp or bee stings, natural latex (rubber), penicillin or any other drug or injection. In some people, exercise can trigger a severe reaction - either on its own or in combination with other factors such as food or drugs (e.g. aspirin).

What are the symptoms?

• generalised flushing of the skin

• nettle rash (hives) anywhere on the body

• sense of impending doom

• swelling of throat and mouth

• difficulty in swallowing or speaking

• alterations in heart rate

• severe asthma

• abdominal pain, nausea and vomiting

• sudden feeling of weakness (drop in blood pressure)

• collapse and unconsciousness

Nobody would necessarily experience all of these symptoms.

Why does anaphylaxis occur?

Any allergic reaction, including the most extreme form, anaphylactic shock, occurs because the body's immune system reacts inappropriately in response to the presence of a substance that it wrongly perceives as a threat.

An anaphylactic reaction is caused by the sudden release of chemical substances, including histamine, from cells in the blood and tissues where they are stored. The release is triggered by the reaction between the allergic antibody (IgE) and the substance (allergen) causing the anaphylactic reaction. This mechanism is so sensitive that minute quantities of the allergen can cause a reaction. The released chemicals act on blood vessels to cause the swelling in the mouth and anywhere on the skin. There is a fall in blood pressure and, in asthmatics, the effect is mainly on the lungs.

What is the treatment for a severe reaction?

Pre-loaded adrenaline injection kits are available on prescription for those believed to be at risk. Adrenaline (also known as epinephrine) acts quickly to constrict blood vessels, relax smooth muscles in the lungs to improve breathing, stimulate the heartbeat and help to stop swelling around the face and lips.

Am I at risk from anaphylaxis?

If you have suffered a bad allergic reaction in the past – whatever the cause – then any future reaction is also likely to be severe. If you have suffered a significant reaction to a tiny dose, or have reacted on skin contact, this might also be a sign that a larger dose may trigger a severe reaction. If you have asthma as well as allergies, getting seen by an allergy specialist is particularly important because asthma can put you in a higher risk category. Where foods such as nuts, seeds, shellfish and fish are concerned, even mild symptoms should not be ignored because future reactions may be severe.