Allergic contact dermatitis

Allergic contact dermatitis (ACD) is a form of contact dermatitis that is the manifestation of a type IV hypersensitivity (delayed hypersensitivity) response caused by contact with a substance; the other type being irritant contact dermatitis (ICD). It differs from classical allergic reactions, which are type I hypersensitivity reactions.

Although less common than ICD, ACD is accepted to be the most prevalent form of immunotoxicity found in humans. By its hypersensitive nature, this form of contact dermatitis is atypical within the population. The mechanisms by which these reactions occur are complex, with many levels of fine control. Their immunology centres on the interaction of immunoregulatory cytokines and discrete subpopulations of T lymphocytes.