Allergic and Irritant Contact Dermatitis

Abstract

Contact dermatitis is an inflammatory skin disease induced by direct contact of a external agent to the skin. It can be classified into two main types: Irritant contact dermatitis and Allergic contact dermatitis. Irritant contact dermatitis represents a non-specific cutaneous response to the toxic or physical effects of environmental agents, while Allergic contact dermatitis represents a specific type IV hypersensitivity reaction to specific haptens. Both types are characterized by a highly variable clinical presentation that includes erythema, papules, vesicles, bullae, scaling and erosions in acute cases, and papules, plaques, lichenification, hyperkeratosis and fisures in the chronic. Pruritus is a very common symptom most frequently associated with Allergic contact dermatitis but also frequent in Irritant contact dermatitis. Furthermore, occasionally pruritus may be the leading or only symptom that guides the clinician to suspect the diagnosis of Contact dermatitis, as it is in the case of Allergic contact dermatitis of the anogenital region or when the process occurs in the elderly. Although the mechanisms underlying the pathogenicity of the inflammatory cutaneous response in irritant and allergic contact dermatitis has been widely studied, little is known about the mechanisms leading to pruritus. This chapter summarizes the most important aspects of contact dermatitis in these specific situations as well as the last insights into the pathogenicity of pruritus in contact dermatitis.