• Defined as generalized redness and scaling involving more than 90% of the body surface area (BSA); occasionally applied to patients with slightly less BSA involvement, e.g. when diagnosed earlier in the course of their disease.

• A clinical presentation for a variety of diseases, often divided into three major categories: (1) primary skin disorders; (2) drug-related (Table 8.1); and (3) malignancies, particularly Sézary syndrome and erythrodermic mycosis fungoides.

• In adults (Table 8.2), the most common primary skin disorders are psoriasis (Fig. 8.1) and atopic dermatitis, with allergic contact dermatitis or pityriasis rubra pilaris (Fig. 8.2) less common.