Testing for contact dermatitis involves placing a patch of the suspected substance or substances on the back. The area must be kept clean and dry for forty-eight hours, after which the various patches are removed, and the individual areas are evaluated for inflammatory responses. A positive response then characterizes a type IV reaction, and avoidance of the offending allergen is the treatment of choice. Thirty milligrams per day of systemic steroids may be required when large areas of the skin are involved (>25 percent of body surface). Otherwise, corticosteroid creams may employed; however, avoidance of the contactant is most crucial.