The document discusses the history and pathogenesis of contact dermatitis. It notes that contact dermatitis can be either allergic or irritant-induced. Allergic contact dermatitis is a type IV hypersensitivity reaction resulting from skin exposure to contact allergens. It affects 15-20% of the population and has a latency period of 2-3 days. Nickel, fragrances and balsam of Peru are common allergens identified on patch testing. Irritant contact dermatitis does not involve sensitization and has a shorter latency period of less than 48 hours.