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.

Atopic dermatitis is characterized by chronically itchy, superficially inflamed skin, often accompanied by allergic symp­toms such as hay fever and asthma. It also occurs in patients whose families have histories of allergies. The disease frequently occurs on the face and at or near the elbows and knees. Although atopic derma­titis is associated with allergies, the skin lesions do not have an allergic mechanism in most patients. Symptoms are commonly worse during the cold part of the year and are aggravated by contact irritants. In some people, skin symptoms appear to be aggravated in part by cer­tain foods or by exposure to inhaled allergens such as pollen.

Once one has been diagnosed as having a particular food allergy, life is not over. On the contrary, a new life can begin when one knows the foods that are safe to eat —and the ones that are not.

When the exact cause of the food allergy remains unknown after all diagnostic tests have been completed, your doctor may prescribe drugs to alleviate the symptoms. (Unfortunately, such drugs cannol cure the allergy itself.) Another approach is the rotary diet, in which no food is repeated within a five-day span, thus reducing symptoms.