Contact Dermatitis

Etiology and Epidemiology

Inflammation in the top layers of the skin, caused by direct contact with a substance, is divided into two subtypes: irritant contact dermatitis and allergic contact dermatitis. Irritant contact dermatitis is observed after the skin surface is exposed to an irritating chemical or substance. Contact dermatitis may occur in any age, and girls are more frequently affected than boys. Allergic contact dermatitis is a cell-mediated immune reaction, also called type IV or delayed-type hypersensitivity. The antigens, or haptens, involved in allergic contact dermatitis readily penetrate the epidermis and are bound by Langerhans cells, the antigen-presenting cells of the skin. The hapten is presented to T lymphocytes, and an immune cascade follows.

Clinical Manifestations

Irritant contact dermatitis is characterized by ill-defined, scaly, pink or red patches and plaques ( Fig. 191.1 ) localized to skin surfaces that are exposed to the irritant. Irritant contact dermatitis is observed frequently on the dorsal surfaces of the hands, often from repeated handwashing or exposure to irritating chemicals.

Diaper dermatitis is a common problem in infants and most commonly is a form of irritant contact dermatitis. The dermatitis is caused by irritation from urine and feces, typically affecting the perianal region and the buttocks while sparing the protected groin folds and other occluded areas. Secondary infection by Candida albicans or bacterial pathogens may complicate diaper dermatitis as well.

Allergic contact dermatitis may be acute (such as Rhus dermatitis) or chronic (such as nickel dermatitis). Acute lesions are bright pink, pruritic patches, often in linear or sharply marginated, bizarre configurations. Within the patches are clear vesicles and bullae ( Fig. 191.2 ). Signs and symptoms of the disease may be delayed for 7–14 days after exposure if the patient has not been sensitized previously. On re-exposure, symptoms begin within hours and are usually more severe. The eruption may persist for weeks. Chronic lesions are pink, scaly, pruritic plaques, often mimicking atopic dermatitis. Even intermittent exposure can result in a persistent dermatitis.