Eczematous diseases are mostly epidermal. They are defined by “spongiotic dermatitis” on pathology, and clinically they may present in one of three stages (acute, subacute, or chronic) and in different contexts (types). The word “eczema” is derived from ancient Greek, meaning “to boil,” a reflection of the acute vesicular stage. Though many physicians and lay people use the word “eczema” synonymously with “atopic dermatitis,” the word “eczema” in this book is used differently. “Eczema” (or “dermatitis”) here is defined as a spongiotic reaction pattern that may present in different locations and contexts, with different names applied. For instance, in the context of atopy, a spongiotic dermatitis could be called atopic dermatitis. Other diseases including pityriasis rosea and dermatophytosis can also cause a spongiotic dermatitis.