Individual flares of atopic dermatitis can be prevented by avoiding triggers of inflammation and can be lessened with frequent emollient application. Some evidence suggests that breastfeeding for at least 4 months prevents or delays the occurrence of atopic dermatitis in early childhood. For infants with a parent or sibling with atopic disease and who are not exclusively breastfed for 4 to 6 months, there is modest evidence that the onset of atopic dermatitis may be delayed or prevented by the use of extensively hydrolyzed casein-based formulas. There is insufficient evidence that soy-based formulas, delaying the introduction of complementary foods beyond 4 to 6 months of age, or other dietary intervention prevents the development of atopic disease. There is no convincing evidence that women who avoid peanuts or other foods during pregnancy or while breastfeeding lower their child’s risk of allergies.
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. Allergic contact dermatitis is a cell-mediated immune reaction, also called typeIV or delayed-type hypersensitivity. The antigens, or haptens,involved in allergic contact dermatitis readily penetrate theepidermis 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. Contact dermatitismay occur in any age, and girls are more frequently affectedthan boys.
Irritant contact dermatitis is characterized by ill-defined, scaly, pink or red patches and plaques (Fig. 191-1). The eruption is localized to skin surfaces that are exposed to the irritant. Irritant contact dermatitis is observed frequently on the dorsal surfaces of the hands in patients, often from repeated hand washing 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 lesionsare bright pink, pruritic patches, often in linear or sharplymarginated bizarre configurations. Within the patches areclear vesicles and bullae (Fig. 191-2). Signs and symptomsof the disease may be delayed for 7 to 14 days after exposureif the patient has not been sensitized previously. On reexposure, symptoms begin within hours and are usually moresevere. The eruption may persist for weeks. Chronic lesionsare pink, scaly, pruritic plaques, often mimicking atopic dermatitis. Even intermittent exposure can result in a persistentdermatitis.
The diagnosis is established by clinical presentation andhistory of exposure to a recognized irritant or allergen.Skin-prick testing and serum IgE levels are not helpful indetermining the cause of allergic contact dermatitis. Patchtesting may be used to determine the allergen causing thereaction in difficult cases.
Figure 191-1 Irritant diaper dermatitis.
Figure 191-2 Allergic contact dermatitis to tincture of benzoin.