Anaphylaxis is a rare, generalized, potentially life-threatening allergic reaction to a particular substance (allergen) to which individuals have previously developed an extreme sensitivity (hypersensitivity). The reaction typically occurs within seconds or minutes or, more rarely, up to a few hours after exposure to such an allergen. Allergens may include insect venom, certain foods, medications, vaccines, chemicals, or other substances. An anaphylactic reaction may be characterized by development of an itchy, reddish rash (hives); a severe drop in blood pressure; swelling and obstruction of the mouth, nose, and throat; abdominal cramps; nausea and vomiting; diarrhea; and severe difficulties breathing. Without immediate, appropriate treatment, the condition may rapidly lead to a state of unconsciousness (coma) and life-threatening complications.
During an anaphylactic reaction, entry of the allergen into the bloodstream triggers the release of large amounts of the chemical histamine and other chemicals from certain cells (e.g., mast cells, basophils). The release of these substances leads to widening (dilation) of blood vessels; an associated, severe drop in blood pressure; and leakage of fluid through blood vessel walls into surrounding tissues. As a result, affected individuals may develop itchy (pruritic), raised white areas on the skin surrounded by reddish inflammation (hives or urticaria); swelling; and stinging or prickling sensations of the skin.
The digestive (gastrointestinal) tract may also be affected, resulting in nausea, vomiting, abdominal cramping, or diarrhea. Excessive release of histamine may also cause severe narrowing (constriction) of the lung’s airways (bronchi), resulting in tightness of the chest, coughing, a high-pitched whistling sound while breathing (wheezing), and shortness of breath (dyspnea). There may also be swelling and associated obstruction of the nose, mouth, tongue, and throat, potentially obstructing the air supply and causing severe difficulties breathing (respiratory distress). Some affected individuals may also develop cardiovascular symptoms such as abnormal heart rhythms (arrhythmias). In addition, a severe drop in blood pressure may lead to an extreme reduction of blood flow throughout the body (shock), leading to lost consciousness (coma) and potentially life-threatening complications.
Anaphylaxis is caused by an excessive immune response (hypersensitivity) upon exposure to a previously encountered foreign substance (allergen). Affected individuals produce certain proteins known as antibodies (i.e., immunoglobulin E [IgE]) that recognize particular allergens as foreign. When an allergen enters the bloodstream, such antibodies are secreted into the blood and react with the foreign proteins, causing certain cells (e.g., basophils, mast cells) to release histamine and other chemicals (chemical mediators) involved in inflammatory responses. The release of these chemicals may result in constriction of the lung’s airways (bronchi), widening (dilation) of blood vessels, and leakage of fluid through blood vessel walls, leading to the symptoms and findings associated with an anaphylactic reaction.
Anaphylaxis may result from injection, inhalation, or swallowing of, or skin exposure to an allergen to which an individual has an extreme, previously developed sensitivity. “Injected” allergens may include insect venom, particularly from wasps, bees, hornets, or fire ants, or injected foreign proteins that are therapeutic agents. These may include vaccines, insulin, certain muscle relaxants, or extracts of the proteins of certain allergens (allergenic extracts) that may be used in the diagnosis or treatment (desensitization therapy) of allergies. Certain medications may provoke a reaction through injection as well as through ingestion, such as certain antibiotics, particularly penicillin. In individuals with extreme sensitivity to latex, an anaphylactic reaction may result from skin exposure to, or inhalation of, particles from latex products. Anaphylaxis due to severe food allergies usually results from consumption of (rather than skin contact with) allergens. Foods that most commonly trigger an anaphylactic reaction include shellfish, nuts, chocolate, eggs, and milk. In rare cases, certain fruits and vegetables such as kiwi or celery have caused anaphylaxis.
According to reports in the medical literature, exercise may also induce anaphylaxis in some cases. In addition, some individuals may develop an anaphylactic reaction when they ingest a particular food and then engage in exercise – yet do not develop a reaction if they perform either activity alone. These cases may be referred to as exercise-induced food anaphylaxis.
In some instances, the specific allergen responsible for triggering an anaphylactic reaction remains unknown (idiopathic anaphylaxis).
Anaphylaxis appears to affect males and females of all age groups in equal numbers. Anaphylaxis is considered a rare disorder, but some researchers believe it may be underdiagnosed, making it difficult to determine its true frequency in the general population.
In individuals who are experiencing anaphylaxis, immediate treatment with epinephrine is essential. Epinephrine is a naturally occurring hormone that is secreted by the adrenal glands in response to impulses from the sympathetic nervous system, a part of the nervous system responsible for controlling involuntary functioning during times of stress. Release of the hormone serves to widen (dilate) the lung's airways, narrow (constrict) blood vessels, and increase the heart rate. Although such therapy is usually effective in arresting an anaphylactic reaction, the episode must be treated as an emergency, requiring immediate medical assistance, thorough evaluation of respiratory and cardiovascular functioning, and additional treatment as required. Additional therapeutic measures may include administration of antihistamine and corticosteroid medications, infusion of fluids into the bloodstream via a vein (intravenous infusion), and oxygen therapy.
Individuals who have previously experienced severe reactions to insect stings or certain foods, medications, or other substances should avoid exposure to the allergen in question if possible. In addition, they should always carry a preloaded syringe of epinephrine for prompt self-treatment or, if incapacitated, for immediate administration by others who have been educated in the proper method of injection.
Some affected individuals may respond to immunotherapy (desensitization therapy), during which gradually increasing doses of purified extracts of the allergen are injected into the skin. The purpose of immunotherapy is to decrease the sensitivity of the immune system to the allergen. However, such therapy carries a risk of causing anaphylaxis and therefore should only be performed with great caution and in a proper medical setting with necessary emergency medications available.
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