Seborrheic keratoses (SKs) are extremely common, benign neoplasms of the epidermis that typically appear on the chest and back. There can be a few or hundreds of these raised, "stuck-on"-appearing papules and plaques with well-defined borders. The etiology is unknown, although there is a familial trait for the development of multiple SKs with an autosomal dominant mode of inheritance.

SKs tend to increase in incidence and number with increasing age. SKs are asymptomatic, but when irritated or traumatized, they may become pruritic or painful with associated redness or bleeding.

SKs rarely arise on penile skin. SKs in the genital area have been associated with the presence of human papillomavirus (HPV) infection as identified by polymerase chain reaction (PCR).

An SK may start out as a flat, wrinkled plaque with a "postage stamp" appearance (flat SK).

A lichenoid keratosis is an inflamed SK that presents as a pink, shiny papule or plaque with an appearance that resembles that of nodular or cystic basal cell carcinoma (BCC) or melanoma.

Melanoacanthoma is an SK subtype characterized by more hyperpigmentation and less hyperkeratosis and often requires a biopsy for definitive diagnosis given the degree of pigmentation.

Relatively rapid onset (within weeks to months) of numerous SKs may be a cutaneous sign of internal malignancy. Multiple eruptive SKs in association with a visceral cancer is referred to as the sign of Leser-Trélat. The most common associated malignancy is adenocarcinoma of the gastrointestinal tract; other associated malignancies include lung cancer, esophageal carcinoma, mycosis fungoides, and Sézary syndrome.