Allergies pose a significant and serious health problem in this country. According to conservative estimates, nearly 15 million Americans are plagued by hay fever and 10 million have asthma. Twelve million more Americans suffer from such allergies as eczema and hives, not to mention allergic reactions to food, drugs, and insect stings. Most of these disorders have a hereditary component and tend to run in families. Basically, an allergic reaction occurs whenever the immune system overreacts to a seemingly harmless substance. Known as allergens, these substances include pollen, mold, house dust, mites, animal saliva and dander (skin shed by cats, dogs, or rabbits), feathers (such as those used in feather pillows), certain foods and drugs, and insect stings. Allergens are usually absorbed into the body by way of the skin, nasal passages, lungs, or digestive tract. Once inside the body, allergens stimulate the lymphocytes (small white blood cells) to produce what are known as allergic antibodies. The reaction between the allergen and these antibodies, which are attached to certain special cells (mast cells), leads to inflammation of the nose, eyes, lungs, and the digestive tract. A stuffy nose, sneezing, wheezing, skin rash, watery eyes, abdominal cramps, and nausea are some of the most common results.