Keratosis pilaris (KP) is a very common autosomal dominantly inherited disorder of follicular hyperkeratosis, affecting 50% to 80% of adolescents and about 40% of adults worldwide. KP is generally described as a skin condition of childhood and adolescence, but may worsen with puberty and pregnancy. Symptoms commonly improve with age. A questionnaire-based study reports some seasonal variation, with improved symptoms in the summer and worsening in the winter.

Several conditions associated with KP include ichthyosis follicularis, atopic dermatitis, papular atrichia, mucoepidermal dysplasia, cardiofaciocutaneous syndrome, and ectodermal dysplasia with corkscrew hairs.

KP is characterized by horny folliculocentric keratotic plugs or small papules (Figs. 26-1 and 26-2). The papules are typically acuminate, may have a surrounding erythema, and dot the otherwise normal skin on the lateral aspects of the upper arms, legs, and buttocks in a fairly regular pattern. Removal of a plug leaves a cup-shaped depression in the apex of the papule, which is soon filled by new keratotic material. The follicular bump is created by keratin accumulation and often a small coiled hair may be trapped beneath the keratin debris. KP is generally asymptomatic except for cosmetic dissatisfaction and mild pruritus. Treatment may prove challenging.

Keratosis pilaris rubra faceii is a variant of KP whereby keratotic papules are located on the face on a background of erythema. KP atrophicans or ulerythema ophryogenes (Fig. 26-3) begins in childhood, involves the cheeks and eyebrows, and is accompanied by madarosis (absence of eyelashes or eyebrows). Epidermal atrophy and perifollicular fibrosis are present. Atrophoderma vermiculata has been described as KP of the cheeks, which results in a honeycombed worm-eaten appearance resembling acne scarring.