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4 + ward ' s science Allergic rhinitis The most frequent manifestation of allergy is allergic rhinitis. Allergic rhinitis was originally misnamed hay fever because it was believed that hay causes the disorder, and "fever" was a term loosely applied to many ailments, even when not ac- companied by fever. However, in addition to nasal symptoms (watery nasal discharge, sneezing, runny eyes, and itchy nose, throat, and roof of the mouth), the individual may experience fatigue, irritability, and loss of appetite. The seasonal form of allergic rhinitis is usually caused by pol- lens from grasses, weeds, or trees. Related symptoms appear only during that time of the year when the pollens to which the individual is sensitive occur in the air. When allergens are pres- ent all the time, allergic rhinitis may occur year-round. Frequent causes include allergens present in the house or workplace, such as dust, molds, and animal danders. Chronic or recurrent rhinitis, however, is not always related to allergy; in many instances, it may be caused by an abnormal irritability of the nose (so-called intrinsic or vasomotor rhinitis). Bronchial asthma The allergic disease that causes the most problems in terms of frequency and severity is bronchial asthma (Fig. 4), which involves acutely occurring shortness of breath and wheezing. Constriction of tiny bronchi in the lung airways, accompanied by an augmentation of bronchial secretions and the swelling of bronchial mucosa, contributes to obstruct the free passage of air through the lungs, producing wheezing. However, wheezing is not always indicative of asthma. Furthermore, in numerous instances, the cause of asthma is not related to allergy against some airborne allergens. It is customary to classify asthma as extrinsic, that is, due to contact with an external allergen, or intrinsic, that is, due to endogenous causes that are still poorly defined (for example, stress or bronchial hyperreactivity owing to hormonal and other factors). Allergic asthma is considered a major public health problem, owing both to its severity and to the possibility of death during an acute and prolonged asthma attack (status asthmaticus). In view of the large variety of possible causes of asthma, differ- ent mechanisms may be operating. In classical cases of allergic asthma that result from airborne allergens, IgE antibodies prob- ably play a major role, but other forms of immune reactions also need to be considered. Food allergies Food allergies may occur as a reaction to natural products (for example, celery, milk, and egg proteins) and to chemicals or preservatives added to foods (for example, dyestuffs and an- tioxidants). An allergy to food may manifest itself at the primary site of contact with the allergen, that is, in the gastrointestinal tract, causing diarrhea, abdominal pain, nausea, and vomit- ing. However, it also may take another form once the allergen has been absorbed, causing symptoms in the upper airways (rhinitis and asthma) and in the skin (hives); in cases of extreme hypersensitivity, generalized anaphylactic shock may result. Occupational allergies Occupational allergies have become increasingly frequent in industrialized countries. Chemicals used in plastic and phar- maceutical industries or in metal refining and construction work are frequent offenders. However, natural organic materi- als, including baker's flour, animal products, castor beans, silk, and furs, may be involved as well. Here, too, the most frequent manifestations involve the upper respiratory tract and the skin. Skin allergies Skin allergies may take several forms. Atopic dermatitis is a chronic superficial itching inflammation of the skin (eczema; Fig. 3), often involving a period of long duration. IgE antibodies frequently are notably increased. In many cases, atopic derma- titis occurs early in life together with cow milk allergy (infantile eczema). Allergic contact dermatitis is characterized by a red rash, swelling, intense itching, and sometimes blisters at the site of contact with the allergen, which may be of plant origin (for example, poison ivy or turpentine) or may be an industrial chemical. Lesions are caused by sensitized lymphocytes and belong to the delayed hypersensitivity type of allergy Urticaria (hives) is a very common manifestation of skin allergy. When evoked by sensitization to some allergen, IgE antibodies are present. Foods, drugs (for example penicillins), Allergy (continued) Fig. 4: Bronchial asthma is often a clinical manifestation of an allergic reaction: (left) anterior view of the respiratory system of an asthmatic patient; (right) a sectioned bronchiole. The airways of a patient suffering from bronchial asthma are narrowed as a result of the inflammatory response, causing wheezing. (Credit: MedicalRF)