Many people experience allergy symptoms which are only a minor annoyance. However, a small number of highly allergic individuals are susceptible to a life-threatening allergic reaction known as anaphylaxis. Anaphylaxis, the most serious type of allergic reaction, is extremely rare. Symptoms usually appear rapidly - within seconds or minutes-after exposure to an allergen (a substance which causes an allergic reaction). In a few cases, however, reactions have been delayed as much as 12 hours.

Symptoms of Anaphylaxis

In anaphylaxis, cells of the immune system release massive amounts of chemicals - particularly histamine. As a result, blood vessels dilate and begin to leak fluid into surrounding tissues, producing swelling. Several organs can be affected:

  • The skin frequently shows symptoms first. Hives, itching, swelling, redness or a stinging or burning sensation may develop.
  • The loss of fluid from blood vessels causes a drop in blood pressure and the individual may feel light-headed or even lose consciousness.
  • Anaphylaxis can cause obstruction of the nose, mouth and throat. Individuals may first notice hoarseness or a lump in the throat. If the swelling is very severe, it shuts off the air supply and the individual experiences severe respiratory distress.
  • The airways in the lungs can constrict, causing chest tightness, shortness of breath and wheezing - the classic symptoms of asthma.
  • The person may experience nausea, vomiting, cramping and diarrhea.
  • The gastrointestinal tract often reacts, especially if the allergen is something that was swallowed.
  • Women may experience pelvic cramps due to contractions of the uterus.

It's worth repeating that anaphylaxis is rare. The vast majority of people with allergies will never have an anaphylactic reaction.

Triggers of Anaphylaxis

An anaphylactic reaction is usually triggered by a limited number of allergic exposures. These include injection, swallowing, inhaling or skin contact with an allergen by a severely allergic individual.

Examples of injected allergens are bee, hornet, wasp and yellow jacket stings; certain vaccines which have been prepared on an egg medium; and allergen extracts used for diagnosis and treatment of allergic conditions. Antibiotics such as penicillin can trigger a reaction by injection or ingestion (swallowing).

Typically, a severe reaction caused by a food allergy occurs after eating that particular food, even a small bite.

Skin contact with the food rarely causes anaphylaxis. Foods most commonly associated with anaphylaxis are peanuts, seafood, nuts and, in children particularly, eggs and cow's milk.

An anaphylactic reaction from an inhaled allergen is rare. An increasingly recognizable example is when an allergic individual inhales particles from rubber gloves or other latex products.

For some people, two or more factors may be needed to cause anaphylaxis. Recently, it has been recognized that some persons have experienced an anaphylactic reaction if they eat a certain food, and then exercise. Neither the food alone nor exercise alone causes any problem for these individuals.

When exposed to a foreign substance, some people suffer reactions identical to anaphylaxis, but in which no allergy is involved. These reactions are called anaphylactoid (meaning anaphylaxis-like) reactions. While the immune system must be "primed" by previous exposure to cause anaphylaxis, anaphylactoid reactions can occur with no previous exposure at all. An example of something that can bring on this kind of reaction is radiographic contrast material (the dye injected into arteries and veins to make them show up on an X-ray).

Fortunately, health care providers don't need to distinguish between anaphylactic and anaphylactoid reactions during an emergency because the treatment is the same.

Prevention of Anaphylaxis

To prevent anaphylaxis, it is important to avoid the allergen that causes the reaction. That may not be easy since stinging insects can find their way indoors and allergenic foods can be concealed in a wide variety of preparations.

Precautions can lower the risk of anaphylaxis and minimize the severity of reactions. For many people, immunotherapy ("allergy shots") can help. For example, immunotherapy for bee, wasp, hornet and yellow jacket stings gives effective protection 98% of the time. There is some risk when an individual with past episodes of anaphylaxis is injected with an allergen, but experienced health care professionals working in a controlled setting can make that risk negligible.

If immunotherapy is not practical or available for a particular allergen, the physician has other options. For example, if someone has experienced an anaphylactic reaction to penicillin, the physician might order skin tests before giving certain other types of antibiotics. In most cases, different classes of antibiotics are available. Individuals who have a history of severe reactions to medications should take a new medication orally (by mouth) whenever possible, because the risk of anaphylaxis is higher with an injection.

Rarely, someone may get an infection that requires treatment with an antibiotic known to cause anaphylaxis in that individual. In this case, rapidly increasing oral (by mouth) doses of the antibiotic under carefully controlled conditions can often desensitize the person.

Physicians sometimes suggest that individuals who have had an anaphylactic reaction carry an epinephrine syringe designed for self-administration.

This is particularly important if the allergen that causes the reaction is difficult to avoid. This type of medication, available by prescription only, is sold under the name Twinject®, EpiPen® or EpiPen Jr.® (for children). We recommend that the patient, and any person who might be in a position to administer the injection, receive training in the use of these syringes. We also recommend that anyone at risk for anaphylaxis wear a Medic-Alert® bracelet.

Some medicines given for high blood pressure (called beta blockers) can partially counteract the effects of epinephrine, making the treatment of anaphylaxis more difficult. Allergic individuals with high blood pressure may need to ask their physician about switching to a different type of high blood pressure medication.

Treatment of Anaphylaxis

If you suspect that an anaphylactic reaction is occurring, immediately seek medical help. Treatment must begin before blood pressure and breathing problems become life-threatening.

Epinephrine is the most important medication for the treatment of anaphylaxis. It is injected under the skin or into a muscle. Epinephrine works rapidly to make blood vessels contract, preventing them from leaking more fluid. It also relaxes airways, helping the individual breathe easier, relieves cramping in the gastrointestinal tract and stops itching and hives.

Even if the individual responds to the epinephrine, it is vitally important to go to an emergency room immediately! Other treatments may be given such as oxygen and medications to improve breathing. Intravenous fluids may be necessary to restore adequate blood pressure. Additional medications may be given to counteract the effects of histamine and to help prevent a delayed allergic reaction.