Anaphylaxis is the most severe of all allergic reactions and can result in difficulty breathing, a sudden drop in blood pressure with subsequent loss of consciousness, and even death. Anaphylaxis is a medical emergency that requires immediate recognition, prompt medical treatment, and follow up care by an allergist.

It has been estimated that up to 15% of the population is at risk for anaphylaxis. Anaphylaxis can occur within minutes after exposure to a substance to which one is severely allergic. The most common substances that trigger anaphylaxis are foods, medications, and insect stings.

Mechanisms of anaphylaxis

Anaphylaxis is triggered when an allergen (food, medicine, insect venom, etc.) comes in contact with antibodies (IgE) in the blood or tissues previously formed by prior exposure to the allergen. This antigen-antibody reaction results in a rapid cascade of cellular events leading to the immediate release of large amounts of histamine and other chemical mediators.

These chemical mediators, when exposed to the smooth muscles of the lungs, can quickly lead to constriction of the bronchial smooth muscle causing wheezing, tightness, and difficulty breathing. Exposure to blood vessels generally causes urticaria, or hives, and can lead to vasodilatation of the peripheral circulation resulting in low blood pressure and possibly shock. Reactions usually begin within seconds to minutes of exposure, but may be delayed. In general, the quicker the onset of symptoms, the more severe the reaction may be. Sometimes symptoms resolve, only to recur or progress a few hours later.

Symptoms of anaphylaxis

Anaphylaxis is, by definition, “systemic”. It therefore can affect multiple organ systems, including the skin, respiratory, circulatory, and gastrointestinal systems. Symptoms of anaphylaxis can vary from mild to severe, and are potentially deadly. The following is a list of possible symptoms that may occur alone, or in any combination:

Skin: hives, swelling, itch, generalized warmth and redness

Breathing: wheezing, shortness of breath, throat tightness, cough, hoarse voice, chest pain/tightness, nasal congestion/hay fever-like symptoms

Gastrointestinal: nausea, pain/cramps, vomiting, diarrhea, itchy mouth/throat, difficulty swallowing

Circulation: pale/blue color, poor pulse, passing-out, dizzy/ lightheaded, low blood pressure, shock

Other: anxiety, feeling of “impending doom,” red/itchy/watery eyes, headache, cramping of the uterus

Substances that trigger reactions

A recent study done at the Mayo Clinic found that food allergy is the most common cause of anaphylaxis. In their study of patients presenting to the emergency room over a ten year period, 33% of anaphylaxis cases were caused by foods. Insect stings accounted for 19% and medications caused 14% of all anaphylactic reactions.

Foods: Essentially any food can trigger an allergic reaction, but the most common ones that cause severe anaphylaxis are: peanuts, tree nuts (e.g., walnut, pecan, almonds, cashew, Brazil nut), shellfish, fish, milk, and eggs.

Stinging insects:The venom of stinging insects such as yellow jackets, honeybees, wasps, hornets are common causes of anaphylaxis, as is the biting fire ant in certain geographical areas of the U.S.

Medications: Virtually any medication can trigger an allergic reaction. Common categories of drugs that cause anaphylaxis are aspirin and other non-steroidal anti-inflammatory drugs (NSAIDS), antibiotics, and anti-seizure medicines. Medical therapies such as certain post-surgery fluids, vaccines, blood and blood products, radio-contrast dyes, pain medications, and other drugs may cause anaphylaxis or anaphylactoid (anaphylaxis-like) reactions.

Latex: Some products made from natural latex from the rubber tree contain allergens that can trigger reactions in sensitive individuals. The greatest danger of severe reactions occurs when latex comes into contact with moist areas of the body during examinations or internal surfaces during surgery.

Exercise: Although rare, exercise can also trigger anaphylaxis. Oddly enough, it does not occur after every exercise session. In some cases, only occurs after eating certain foods prior to exercise.

Other: Anaphylaxis has rarely been associated with exposure to seminal fluid, hormones, and exposure to extreme temperatures. When no cause is found it is termed idiopathic anaphylaxis.

Treatment and prevention

In addition to the administration of rapid acting antihistamines, the effective medical treatment of anaphylaxis requires the immediate administration of epinephrine (adrenalin). The quicker epinephrine is given to the onset of symptoms, the better likelihood of successful treatment. It is sometimes necessary to give a second or even a third dose if symptoms persist. While medical treatment is being initiated, medical assistance should be sought as further therapy may be necessary. Even after receiving immediate medical treatment on site, one should be transported to a medical facility or hospital for further evaluation.

What type of follow up is necessary?

Any person who has had an anaphylaxis episode should consult an allergist in order to:

• determine if you have had, or are at risk for anaphylaxis
• determine what allergen(s) may cause your reaction
• advise you as to whether or not any medications you are taking might make anaphylactic episodes worse or interfere with treatment and suggest alternatives
• teach you how to avoid the allergen(s)
• provide education about recognizing symptoms of an anaphylaxis
• create a written emergency treatment plan for use by you and others
• teach you how to use self-injectable epinephrine
• prescribe self-injectable epinephrine
• offer the most up-to-date therapies to treat and/or prevent subsequent reactions