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Chapter 3. Allergic Contact Dermatitis

Integration: Unifying Concept

What has been written about clinical diagnosis of allergic contact dermatitis applies in principle to irritant contact dermatitis. Distribution, in addition to character of individual lesions, is decisive.

Irritant contact dermatitis is unrelated to hypersensitivity and is inducible in every human being by virtue of the intrinsically damaging character of an irritant, the earliest stage being red macules or patches that very soon are surmounted by vesicles, bullae, or both.

All of the morphologic expressions of allergic contact dermatitis and of irritant contact dermatitis are a consequence of a basic pathologic process, to wit, delayed hypersensitivity for the former and nonhypersensitivity, irritation, often with necrotizing effects, for the latter. In short, papules, vesicles, and bullae that develop in response to contact allergens and contact irritants are a reflection of an inflammatory process that involves the dermis and epidermis, the dermis first for allergic contact dermatitis in regard to where changes pathologic are witnessed initially and the epidermis first for irritant contact dermatitis. Conceptually, the epidermis is the first affected in allergic contact dermatitis, that being the site where a haptene forms without which the immunologic process could not commence. Spongiosis with little if any ballooning or necrosis is present in the case of allergic contact dermatitis, and ballooning accompanied by necrosis and little if any spongiosis is manifest that of irritant contact dermatitis.