Dermatitis, contact

Contact dermatitis is inflammation of the skin caused by an exogenous substance that either has a direct toxic effect (irritant contact dermatitis) or that causes an immunologic reaction (allergic contact dermatitis).

Irritant and allergic contact dermatitis can be caused by a bewildering array substances ranging from detergents to plants. For this reason it is extremely common and is an important cause of occupational illness. The lesions of contact dermatitis appear acutely as vesicles and chronically as lichenification.

Irritant contact dermatitis usually appears within several hours of contact but may, with weaker irritants, take days to develop. Allergic contact dermatitis usually appears 24-48 hours after exposure.

Common causes of allergic contact dermatitis are poison ivy or poison oak; nickel; cosmetics; rubber/latex; and medications.

Poison Ivy/Poison Oak/Poison Sumac. Chemicals in the sap (oleoresin/usushiol) of the plant act as sensitizing allergens. It characteristically manifests as linear streaks of vesicles and papules., corresponding to an area where a leaf brushed against the skin. It is not spread by scratching the skin. Once sensitized to a member of this plant family, other non-obvious members of the family must be avoided including: mango, cashew, and ginkgo.

Cosmetics. A common offender is paraphenylenediamine, a dye used in hair coloring and other products. It causes allergic contact dermatitis in persons that have their hair colored and, occupationally, in hair dressers. It is also a cause of allergic contact dermatitis to henna tattoos, which sometimes include paraphenylenediamine as a darkening agent.

Nickel. Allergic contact dermatitis to nickel usually corresponds to locations where jewlery is worn, such as earlobes, wrists, fingers, and belt buckle area.

Rubber/Latex. Rubber allergens are often found in shoes and gloves. Latex allergy is common in healthcare workers. Dermatitis limited to the hands or feet is typical, but spread of allergen to other areas is not uncommon.

Medications. Allergies to the common topical antibiotics neomycin and bacitraicin are common.

With what can it be confused?

Contact dermatitis can be confused with other causes of dermatitis, fungal infections and bacterial Cellulitis.

How is it diagnosed?

Morphologically, the lesions of contact dermatitis do not differ from those of other causes of dermatitis. A detailed history of environmental, occupational, and recreational exposure to potential irritants and allergens is necessary. The shape of the lesion (e.g. streaks, sharp margins) and location (e.g. hands or feet) may provide important clues. There is no specific way to diagnose irritant contact dermatitis. Allergic contact dermatitis can be tested for by a screening patch tests, in which a standard panel of allergens is placed on the skin and then examined after 48 hours for evidence of delayed sensitivity. Biopsy is not helpful

How is it treated?

Severe generalized contact dermatitis can be treated with a short course of sytemic steroid (e.g. prednisone). Symptoms of widespread dermatitis can be treated with baths, with or without additives such as colloidal oatmeal (e.g. Aveeno) or tar (e.g. Cutar). Astringent dressings (e.g. Domeboro) are also beneficial. Pruritus can be relived with antihistamines such as hydroxyzine or diphenhydramine. Antibiotics (anti-Staph spectrum) are required in the event of secondary infection. For milder, localized lesions, topical corticosteroids are the mainstay of treatment. Typical topical preparations, in order of increasing potency, are hydrocortisone 1%, triamcinolone 0.1%, and fluocinonide 0.05%. Pruritus can be relived with antihistamines such as hydroxyzine or diphenhydramine.

What is the prognosis?

Acute contact dermatitis usually resolves within several weeks. Continued contact with the irritant or allergen can lead to chronic contact dermatitis. Secondary infection can occur. Generalized skin hypersensitivity and generalized dermatitis can develop, as well.

How is it prevented?

Avoidance of offending irritants or allergens is often easier said than done, especially when the offending substance is found at one's place of employment. Protective clothing may help. A Barrier cream, such as Ivy Block, can prevent poison ivy, but it is specific for this allergen.

Date created: 01/03/2009

Last updated: 01/03/2009