Most people think that allergy is the body of a certain type of stimulus over-sensitive, this is not entirely. Allergic reactions, also known as allergic refers to the body by antigen (including semi-antigen) to stimulate, to produce antibodies or sensitized lymphocytes, when the re-engagement with a post-antigen in the body caused by body fluids or cell immune response This led to the body tissue injury or physical dysfunction. Allergy is divided into four general types:

(1) Ⅰ, also known as allergic-type speed-sensitive, IgE-dependent reaction, such reaction is mainly due to the antigen and IgE antibodies arising from the interaction. Smooth muscle spasm caused by local, increased permeability of blood vessels, congestive heart microvascular expansion, plasma extravasation, such as edema and histological changes. Ⅰ belong to the type of allergic skin URTICARIA there, blood vessels, such as edema.

(2) Ⅱ-allergy drug, also known as cell-type reaction, is the body produce its own components of the cell or cell antigen in the fixation of the antibody, with the corresponding antigen antibody reaction occurs when, due to complement participation in the occurrence and solution cells or tissue injury. Ⅱ belong to the type of allergic skin disease have a drug-induced anemia, thrombocytopenia purpura, pemphigus and pemphigoid, and so on.

(3) Ⅲ, also known as allergic-type immune complex reaction, immune complex refers to have some kind of antigen of the settlement of the antigen and antibodies to form antigen-antibody complex, the complex easier to cool the vessel wall in the basement membrane And around, the occurrence of a small vessel wall as the center of change, which occurred in organs and tissues of the injury. Ⅲ belong to the type of skin allergy are: allergic vasculitis, lupus kidney disease, such as serum.

(4) Ⅳ-called delayed-type hypersensitivity response, the body as a result of such response is stimulated by antigen, T lymphocytes into the sensitized lymphocytes, cells that once again encountered the corresponding antigen, often 1 to 2 days after the release of a series of lymphokines, causing tissue injury or damage to the target cells. Ⅳ belong to the type of allergic skin disease: contact dermatitis, eczema, tuberculin skin-reaction.

Some skin allergies are more complex mechanism, can not belong to a particular type of allergy, such as atopic dermatitis are based Ⅰ and type Ⅳ, and the drug eruption include all types of allergy.