Xerosis (dry skin, asteatosis) is one of the most common dermatologic conditions, characterized clinically by dry, rough, and scaly skin. It is frequently found in the elderly population and in those living in dry climates. Xerosis more commonly involves the lower legs; however, any site may be affected. Asteatotic eczema, a condition frequently found in the elderly during the wintertime, is a superimposed dermatitis on xerosis. Dry skin can result from both endogenous and exogenous causes. Endogenous causes include malnutrition leading to hypovitaminosis, renal disease, underlying malignancies (especially Hodgkin lymphoma), human immunodeficiency virus, hypothyroidism, and hereditary diseases such as ichthyosis vulgaris and atopic dermatitis. Exogenous causes include cold, dry, windy climates, low indoor humidity, excessive exposure to water, soaps and surfactants, and drugs (i.e., lithium, diuretics, and isotretinoin). The pathogenesis of xerosis may be attributed to a decrease in stratum corneum lipids, resulting in impaired barrier function and decreased synthesis of the “natural moisturizing factor.” This results in reduced water-binding capacity of the stratum corneum leading to dehydration of the stratum corneum and the formation of dull, rough scales. This sequence of events may be a result of exposure to exogenous factors or represent dysfunction of the stratum corneum as a consequence of aging.

Ichthyosis vulgaris is an autosomal dominant disorder of keratinization with a prevalence of 1 in 250 individuals. It results from a loss of function mutation in the filaggrin gene. Filaggrin deficiency results in impaired squamous cell formation and transepidermal water loss. Clinical manifestations are not present at birth, typically appearing early childhood. The clinical findings in ichthyosis vulgaris overlap with xerosis and often cannot be differentiated (Table 13-1). Ichthyosis vulgaris is frequently associated with the atopic triad of asthma, allergic rhinitis, and atopic dermatitis. Laboratory workup may reveal endogenous or exogenous causes of dry skin discussed previously (Table 13-2).

Mild xerosis is usually asymptomatic, but severe xerosis is often associated with pruritus and a stinging sensation. Xerosis initially starts on the lower legs, then spreads to involve the proximal extremities and trunk, often sparing the face, neck, palms, and soles. The skin appears dry and dull, with bran-like scales. With more severe involvement, the skin exhibits superficial cracks and fissures in a pattern that has been likened to a “dried riverbed.” With asteatotic eczema, there is underlying erythema often with excoriations, crusting, and nummular plaques present.

Ichthyosis vulgaris is characterized by fine, white, flaky scale especially on the extensor surfaces of the extremities (Fig. 13-1). The scales on the lower legs tend to be larger with an adherent center and detached outward edges. Flexural areas are spared secondary to increased humidity in these areas. Keratosis pilaris (follicular accentuation and keratinization) may be prominent over the arms, thighs, and buttocks. The palms and soles may have mild hyperkeratosis leading to accentuated skin lines.