The occasional skin reaction to a drug or plant, the last in this group of allergy emergencies, can become so extensive that it poses a real danger. Poison ivy or oak may produce such a skin reaction. The skin may blister. Intact skin protects against bacteria and allows the exchange of salts and water needed to prevent the body from overheating. If enough skin is involved, the victim risks complications from the partial loss of skin. If damage to the skin is extensive enough, fever, chills, skin abscesses, and blood-borne infections may occur. The skin inflammation (dermatitis) that results from contact with poison ivy, cosmetics, metals, or chemicals is called, appropriately, contact dermatitis; antibodies are not involved. Cells called lympho­cytes become sensitized to the chemicals and, upon reexposure to the chemicals, enter the skin in an effort to remove the invading material. In the ensuing effort, the lymphocytes call in helper cells —macro­phages. Macrophages, literally "big eaters," may damage normal tissue in the process of clearing up the invaders. It generally takes about forty-eight hours after the chemical enters and the cells re­spond for skin damage to be visible. An even more severe dermatitis may result —not from external contact this time, but from drugs taken internally. Some of the earlier, long-acting sulfa preparations were responsible for such severe blistering that large areas of the skin were shed, a condition physicians call exfoliative dermatitis. Today, few of the drugs com­monly used cause such reactions. It is always possible, however, that a new drug will be approved before an adverse reaction is discovered. Severe anaphylaxis, unremitting asthma, acute edema of the larynx, and extensive contact (or exfoliative) dermatitis must all be considered true emergencies. Emergencies, though, may also arise from the side effects of the drugs used to treat these and other allergic diseases. Serious side effects are usually due to a relative over­dose of a drug. The overdose may be caused not only by receiving or taking more than the usually prescribed amount but because of the body’s metabolism of the particular drug or because the excretion is slower than normal. The end result is an accumulation of high or toxic levels of the drug or drugs. Among antiallergy drugs, the bronchodilators used to treat asthma cause the bulk of serious side effects. (A list of undesirable reactions appears in Table 3.3.) Nonemergency Allergic Reactions The conditions described below are more annoying than danger­ous. Familiarity with their symptoms and causes should alleviate alarm and lead to proper treatment.

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