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

Contact dermatitis presents as either allergic or irritant in etiology. While irritant contact dermatitis represents the direct toxic effect of an offending agent on the skin, allergic contact dermatitis (ACD) represents a delayed-type (type IV) hypersensitivity reaction that occurs when allergens activate antigen-specific T cells in a sensitized individual. Consequently, whereas irritant contact dermatitis can occur after one exposure to the offending agent, ACD typically requires repeat exposures before an allergic response is noted. Allergic contact dermatitis can occur 24-48 hours after exposure to the offending agent.

ACD can occur in response to topical agents, systemic exposure via ingestion or implanted devices, or innocuous transfer of the culprit agent via the fingertips, such as a reaction to artificial nails.

Cases of vulvar ACD have been reported to topical medications such as nifuratel, an antibiotic, and topical anesthetics used to treat hemorrhoids, as well as contact with external materials such as sanitary pads, textiles, or panty hose. In 4%-5% of cases, sensitization to topical steroids has been implicated.

With regard to systemic exposure, clinically relevant reactions to spice and flavor allergens have been noted in a considerable number of cases of anogenital ACD. For example, one case of vulvar ACD was reported in response to sensitization and exposure to peppermint oil by drinking herbal tea. Additionally, nickel sensitivity has been noted in a subset of women with vulvar pruritus, and 50% of these patients had improvement in their symptoms with nickel avoidance. Medical devices such as intrauterine devices for contraception, diaphragms, and condoms have also been implicated. Exposure to inhaled substances including pollen and latex have been reported to cause vaginal ACD.