This summary discusses adult patients. Allergic contact dermatitis in children is addressed separately.

Allergic contact dermatitis (ACD) is a delayed-type (type IV) hypersensitivity reaction that occurs when allergens activate antigen-specific T cells in a sensitized individual. It typically requires repeated exposures before an allergic response is noted and most commonly occurs 24-48 hours after exposure to the offending agent.

ACD can occur in response to topical agents, systemic exposure via ingestion, or innocuous transfer of the culprit agent via the fingertips.

Use of soap, topical anesthetic agents, spermicides, rubber accelerators found in condoms, and topical steroids have all been reported to cause ACD in the genital area. Lipstick-induced penile dermatitis has not been reported but is noted as a theoretical concern for individuals sensitive to octyl gallate.

ACD can present as a systemic contact reaction with widespread lesions when the offending agent is ingested, present in an implanted device, or used in a manner that covers a large portion of the body (eg, body washes). Baboon syndrome (symmetric, sharply demarcated erythema of the gluteal or inguinal area as well as other intertriginous or flexural sites) has also been reported as a presentation of systemic ACD.

Passive transfer of poison ivy resin is also a cause of penile ACD.

The intense erythema and sharply demarcated plaques of contact dermatitis are easy to confuse with cellulitis or erysipelas, especially when vesiculation and bullae formation take place. Differentiating features include the presence of pruritus (often extreme) in contact dermatitis versus the skin warmth and spreading erythema of a soft tissue infection. A detailed allergen exposure history should be elicited.

Related topic: irritant contact dermatitis