Contact dermatitis causes itching and burning. It is characterized by redness, which can progress to vesiculation, oozing, weeping, scaling, and fissuring. After several days of itching and rubbing, the patient may develop secondary bacterial infection with purulence and crusting in the area. Sometimes, the reaction is so intense that swelling occurs at the contact site and dermatitis occurs at distant sites. The latter phenomenon is called an id reaction. Contact dermatitis may be divided into two groups: irritant and allergic.

Irritant contact dermatitis occurs every time the patient comes into contact with the substance. This dermatitis can develop in a few minutes or in several hours. Any person is subject to irritant dermatitis if he or she is in contact with an irritating substance long enough to produce a reaction. The duration of exposure required to produce dermatitis varies. Perhaps the most common contact irritant is soap, especially in the wintertime, when the skin is already dry and irritated. Other common irritants include detergents, cutting oils, solvents, and cement.

Allergic contact dermatitis develops within 24 to 48 hours of exposure to an allergen to which the patient has previously been sensitized. Rhus dermatitis, caused by poison oak, poison ivy, or poison sumac, is the prototypical allergic response. This dermatitis lasts for 10 to 20 days because the rhus oil becomes embedded in the skin. A clue to the diagnosis is its linear pattern. Other common contact allergens include nickel, neomycin, rubber (latex), paraphenylenediamine, lanolin, topical anesthetics, topical antihistamines, and fragrances. It is worth remembering that most metal jewelry contains nickel, even when it is advertised as “solid gold.” The alloy is used to strengthen the gold or silver and also to save expenses. Generally, 18-kt gold has an insufficient amount of nickel to cause trouble (Fig. 3-1). Topical neomycin is the most common cause of iatrogenic allergic contact dermatitis.