Contact Dermatitis (cont.)

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What are risk factors for contact dermatitis?

Contact dermatitis is caused by the direct application of the inciting substance to unprotected skin. Therefore, the key risk factor is exposure to that substance.

What are contact dermatitis symptoms and signs?

Contact dermatitis appears as a weepy, oozy, red, elevated rash (an eczematous dermatitis) at the site of direct contact with the inciting substance. The major complaint of most patients is itching or burning at that site. Older lesions are itchy but may only appear as red, elevated, and scaly.

How is contact dermatitis diagnosed?

Irritant contact dermatitis is diagnosed by its clinical appearance associated with appropriate historical clues furnished by the patient during the medical interview. The incubation period between exposure and the onset of symptoms is minutes to hours so that the patient usually is aware of the identity of the causal substance. Allergic contact dermatitis is much more difficult to diagnose. The pattern of the distribution of the eczematous dermatitis is frequently helpful. For example, allergic contact dermatitis to poison oak, poison ivy, or poison sumac (Toxicodendron plants) typically appears as a linear eruption because the affected skin moves past the leaves of the plant in a line, distributing the allergenic material linearly. The induction of sensitivity requires at least one previous exposure. However, for mildly allergenic substances, many exposures may be necessary before an allergy is manifest. To correctly identify a particular allergen, it may be necessary to use a challenge technique called "patch testing" to confirm which substance is the cause. This requires at least a 48-hour application of the potential allergen to the skin under an occlusive covering. The development of an eczematous dermatitis at the test site within two to five days after removal of the occlusive material confirms the presence of allergy to that substance. Other eczematous eruptions need to be excluded. This may require culturing for microorganisms, an evaluation of skin scrapings and scale, and perhaps a microscopic examination of a small piece of affected skin removed surgically.