The term “eczema,” often referred to redundantly as “eczematous dermatitis,” casts a wide net and tends to be confusing to most nondermatologists. Despite being the most common inflammatory skin condition, eczema is the most confusing skin ailment for both patients and their nondermatologic health care providers. Eczema is very difficult to define. United States Supreme Court Justice Potter Stewart once said that he could not define pornography, but he knew it when he saw it. Such is the case with eczema, a condition that is best understood through repeated viewing (see Chapter 4: Eczema in Infants and Children for a more precise definition).

At one end of its clinical spectrum there is acute eczema (e.g., poison ivy), manifested by itchy red patches, edema, plaques, or papules that may become intensely inflamed and often develop into vesicles and bullae (Fig. 13.1). Subacute eczema is an intermediate stage between acute and chronic eczema. The term has little clinical value but is sometimes used to describe the stage when the acute oozing lesions become dry crusts (Fig. 13.2). On the other end is chronic eczema (e.g., lichen simplex chronicus) whose hallmark is “lichenification,” a thickened plaque with an accentuation of the normal skin lines. It is the result of repeated rubbing of the skin. Lichenification was so named because it resembles the lichens found on tree trunks (actually, it more closely resembles the bark of a tree) (Figs. 13.3 and 13.4).