Allergic Reactions

Basics

Allergic reactions are serious and potentially life-threatening, and can cause injury to tissues throughout the body. Some people have hypersensitive immune systems that overreact to otherwise harmless things such as bee stings, foods, medications, and latex. Reactions range in severity: one person may break out in hives after eating shrimp; another may feel his or her throat closing up. In some cases, the person might pass out or have a heart attack. Without immediate medical treatment, allergic reactions can be fatal.

Causes

Allergic reactions involve proteins called antibodies that react to foreign substances called allergens—such as insect venom, a drug, or certain foods. In sensitive individuals, being exposed to an allergen for the first time stimulates the body to produce antibodies to that allergen. These antibodies bind to special cells in the blood (basophils) and tissues (mast cells). When the individual is re-exposed to the allergen, those bound antibodies trigger the release of histamine and other chemicals that cause swelling and damage surrounding tissues.

• Insects. Some sensitive people have an allergic reaction after getting stung or bitten by an insect. Bees, wasps, yellow jackets, hornets, or fire ants are common culprits.
• Drugs. Certain drugs, vaccines, and dyes used for medical tests may trigger a reaction [Table 1]. Penicillin and similar antibiotics are the most frequent examples. Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDS—ibuprofen and others) are others. Some cancer patients are allergic to chemotherapy drugs, and certain people with diabetes cannot tolerate insulin injections. Others are hypersensitive to the dyes used for diagnostic tests, such as the contrast dye used in CT scans. Some people receiving treatment to prevent allergic reactions may even be allergic to these preventative drugs.
• Food. Eating certain foods or food additives can cause allergic reactions [Table 2]. Peanuts, other nuts such as cashews and walnuts, and seeds are some common offenders. Some people are highly allergic to seafood—shellfish in particular. For others, eating certain types of fruit—such as apples, bananas, peaches, oranges, and melons—can trigger an allergic reaction. Dyes and other additives used in foods have been known to cause reactions as well.
• Some people experience reactions in response to the heat or the cold. Vigorous exercise can result in breathing problems.