Lesions can present in linear or square patches or develop at telling sites such as underneath a watch, on the earlobes, or under a waistband. Allergic contact dermatitis of the face can result in swollen, red, and blistered skin. The responsible allergen is sometimes difficult to determine because there's been exposure to multiple reaction-inducing agents. For example, someone may react to a cosmetic applied to the face, a chemical on the hands, or an airborne allergen, all of which may appear as similar reactions. Irritant contact dermatitis can produce a range of symptoms from mild redness to severe chapping to blisters and ulcerations on exposed areas.
Most cases develop slowly, after repeated exposure to mild irritants.
Harsh, irritating chemicals in high concentrations can cause dermatitis on anyone's skin. A careful medical history is the best tool for diagnosing contact dermatitis. Attention to recent and new as well as long-term exposures is important. Patch testing may be performed when allergic contact dermatitis is suspected. During this procedure, various suspected and common allergy-inducing substances are taped to the patient's back for 48 hours.