Seborrheic keratoses are common benign skin growths. Mostly asymptomatic and only occasionally pruritic, they can manifest as solitary or multiple lesions. Common sites include the head, neck, and back. They are usually verrucous, scaling, and sharply differentiated from the surrounding skin (Fig. 32-1). The color varies from flesh-colored to black or even red, if irritated or inflamed. Seborrheic keratoses can be flat or raised and range in size from less than 0.5 cm to more than 3 cm in diameter. Slow enlargement over the years is normal. Rapid development of multiple lesions occurs rarely (Leser–Trélat sign) and can be a paraneoplastic phenomenon associated with gastric and
other adenocarcinomas. A variant, called dermatosis papulosa nigra, appears as multiple small, dark seborrheic keratoses on the faces of African Americans. Stucco keratoses are multiple, white 0.2- to 0.4-cm seborrheic keratoses on the lower legs or arms. The cause of seborrheic keratoses is unknown but there has been recent evidence suggesting a possible contributing role for some strains of wart virus.