ABSTRACT
Contact dermatitis is defined as inflammation of the skin invoked as a result of exposure to an exogenous agent and constitutes a key portion of occupational disorders in industrialized societies.
In 1898, contact dermatitis was first appreciated to have more than one mechanism and is now generally divided into irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD) on the basis of these mechanistic differences. ACD is a delayed (type IV) hypersensitivity reaction, mediated by T cells and requiring prior sensitization, while ICD has a nonimmunological mechanism, thus not requiring sensitization. Clinical distinction of the two processes is often challenging, as morphology and histopathology of irritant and allergic dermatitis reactions can be virtually indistinguishable. The two processes may, and often do, coexist, thereby further complicating matters.
