• Begin to appear during the 4th decade of life and then gradually increase in number.

• Macular, papular, or verrucous; colors vary from white to black but most commonly brown.

• Typically has a ‘stuck-on’ appearance with a smooth to verrucous surface (Fig. 89.1).

• Spares the palms, soles, and mucosal surfaces.

• May resemble a melanoma clinically but has no pigment network (by dermoscopy) and has horn pseudocysts.

• Sudden appearance of multiple lesions may be associated with internal malignancy (sign of Leser–Trélat) or erythroderma; the former may also be associated with skin tags, irritated seborrheic keratoses, tripe palms, and acanthosis nigricans.

• Histopathology: a spectrum of different architectures, most commonly acanthotic, papillomatous and hyperkeratotic, or irritated (Fig. 89.2).

• Variants:

– Dermatosis papulosa nigra (Fig. 89.3): common in dark-skinned individuals; 1- to 5-mm hyperpigmented papules on the face.

– Stucco keratosis (Fig. 89.4): 1- to 4-mm gray-white papules on the lower extremities (especially dorsal feet and ankles) of older adults.

– Inverted follicular keratosis: endophytic variant of seborrheic keratosis; tan to pink papule, typically on the face of adults.

• Autosomal dominant disorder; sometimes associated with Darier disease.

• Multiple, skin-colored, flat-wart-like papules on dorsal aspect of hands and feet.

• Benign neoplasm of keratinocytes showing papillomatosis with overlying hyperkeratosis in ‘church spires’.

• May have ATP2A2 gene mutation.

• Red, shiny papule or plaque, sometimes with a peripheral collarette of scale (Fig. 89.5).

• Favors the leg.

• Histopathology: acanthosis of characteristically well-demarcated pale or clear keratinocytes with overlying parakeratosis.