When someone with an allergy to something comes into contact with whatever it is, it causes an allergic reaction. A common type of allergic reaction, affecting as many as 15 percent of the population, is called anaphylaxis or, when it is sudden and severe, anaphylactic shock. People experiencing an anaphylactic reaction will experience itching, a tightening of the throat and swelling of the tongue which make breathing difficult, dizziness, a rapid pulse, and nausea or diarrhea.
Anaphylactic shock can be dangerous, even fatal. In fact, anaphylactic shock kills about 1,000 Americans each year. It is generally the result of a food or medicine allergy—the "Big Eight" allergens are milk, eggs, fin fish, shellfish, tree nuts, peanuts, wheat and soy, and penicillin allergies are common—or bee or wasp stings, though it can result from a variety of factors, including latex and even exercise. The reaction often gets more severe with each exposure.
Now researchers say a new discovery gives a clearer picture of the causes and mechanisms behind anaphylaxis than ever before. The reaction involves a chemical, platelet-activating factor, released by cells as part of the immune response, sch as to an allergen. Ordinarily, this chemical is broken down shortly after it is produced and has done its work by a enzyme called PAF acetylhydrolase. When someone is having an allergic reaction, PAF is released despite there being no actual need for an immune reaction. In addition, in some people, there are low levels of PAF acetylhydrolase, meaning it breaks down PAF more slowly. The researchers found that people with the most severe anaphylactic reactions were the people with the lowest levels of PAF acetylhydrolase.
The best way to prevent anaphylaxis is to avoid thing that trigger it, though that can be difficult for people who’ve never had a reaction to anything before. An allergy to one thing doesn’t necessarily mean an allergy to anything else, but as the immune system develops a response to a particular trigger, the reaction tends to get worse as more PAF is produced each time. People who know they are prone to allergic reactions should always have epinephrine available; the hormone, which when administered immediately can help attenuate the reaction, is available in auto-injection pens. A person who has had an anaphylactic reaction needs emergency care even with a pen.