Allergies are the hypersensitive response of the body to foreign substances. These foreign substances are called antigens, which stimulate the body to produce antibodies, whose normal function is to combat antigens by destroying them or otherwise making them harmless. In allergic individuals, for poorly understood reasons, the body's antibody defense mechanism goes awry and injures the body instead of protecting it.

The most familiar allergies are hay fever and asthma, which are caused by a wide variety of inhaled pollens, dusts, and other agents. However, food can also be a cause of allergic reactions.

Food does not often cause allergic reactions. Food allergies are more common in infants than in older children and adults, probably because the infant's immature digestive tract permits more ready absorption of offending food molecules.

Manifestations of food allergies in adults are usually of the immediate kind, including hives, angioderma, eczema, gastrointestinal disorders, and general systemic reactions of the anaphylactic type. Systemic reactions occur quickly after eating.

They are most frequently caused by legumes, nuts, seafoods (especially shellfish), and berries, but carbohydrates, fats, food additives, and contamination by drugs may be implicated.

In infants and children, eczema is the prominent manifestation, and the most frequent causative agents include milk, wheat, eggs, fish, and soybean products.

Food allergies are diagnosed on the basis of the patient's allergic history together with trial eliminations of suspected foods from the patient's diet. Skin tests and tests for antibodies in serum are less significant, because the hypersensitive reaction may be provoked by the breakdown of products of the food resulting from digestion, and not by the food itself.

The management of food allergy is based mainly on the avoidance of the offending foods. An antihistamine taken before a meal may be helpful if a food to which one is allergic is to be eaten. Food allergies in children tend to lessen or disappear with age, but the anaphylactic types manifested in adults do not usually improve over time.