Salem Press

Magill's Medical Guide covers diseases, disorders, treatments, procedures, specialties, anatomy, biology, and issues in an A-Z format, with sidebars addressing recent developments in medicine and concise information boxes for all diseases and disorders. Below is an excerpt from the Guide's essay on allergies.

Allergies
Allergies represent inappropriate immune responses to intrinsically harmless materials, or antigens. Most allergens are common environmental antigens. Approximately one in every six Americans is allergic to household materials such as dust, molds, dust mites, animal dander, or pollen. The effects range from a mere nuisance, such as the rhinitis associated with hay fever allergies or the itching of poison ivy, to the life-threatening anaphylactic shock that may follow a bee sting. Allergies are most often found in children, but they may affect any age group.

Microscopic pollens, which are responsible for many allergic reactions. (PhotoDisc)

Allergy is one of the hypersensitivity reactions generally classified according to the types of effector molecules that mediate their symptoms and according to the time delay that follow exposure to the allergen. P.G.H. Gell and Robin Coombs, defined four types of hypersensitivities. Three of these, Types I through III, follow minutes to hours after the exposure to an allergen. Type IV, or delayed-type hypersensitivity (DTH), may occur anywhere from twenty-four to seventy-two hours after exposure. People are most familiar with two of these forms of allergies: Type I, or immediate hypersensitivity, commonly seen as hay fever or asthma; and Type IV, most often following an encounter with poison ivy or poison oak.