The cause of seborrheic keratosis is unknown, but genetic mutations have been identified in certain types. The lesions commonly occur in middle age and later and most often appear on the trunk or temples. In darker-skinned people, multiple 1- to 3-mm lesions can occur on the cheekbones; this condition is termed dermatosis papulosa nigra.
Seborrheic keratoses vary in size and grow slowly. They may be round or oval and flesh-colored, brown, or black. They usually appear stuck on and may have a verrucous, velvety, waxy, scaling, or crusted surface.
Seborrheic keratoses that are large, multiple, and/or rapidly developing can be a cutaneous paraneoplastic syndrome (Leser-Trélat sign) in patients who have certain cancers (eg, lymphoma, gastrointestinal cancer).
Lesions are not premalignant and need no treatment unless they are irritated, itchy, or cosmetically bothersome.
Lesions may be removed with little or no scarring by cryotherapy (which can cause hypopigmentation) or by electrodesiccation and curettage after local injection of lidocaine.