Mechanisms involved in allergic contact dermatitis.

Allergic contact dermatitis is a common inflammatory skin disease caused by agents such as plants, chemical compounds, and topical medications. Histologic features typically include edema within the epidermis and dermis and a lymphohistiocytic infiltrate with an admixture of basophils. Langerhans cells and keratinocytes play pivotal roles in allergic contact dermatitis reactions. Langerhans cells synthesize and express class II molecules that allow the presentation of exogenous antigens to T lymphocytes. Additionally, keratinocytes and Langerhans cells produce interleukin-1, which is thought to be a second signal that activates T cells. Mast cells and basophils also may play a proinflammatory role. Treatment primarily consists of removal of the offending agent. At times, systemic corticosteroids may be required, especially in the acute phase. In more chronic cases, topical corticosteroids may be beneficial. Antihistamines may be useful because of their soporific effects, but their usefulness is limited.