- Seborrheic Keratoses (SKs) are extremely common slow-growing benign neoplasms of the epidermis that characteristically manifest as waxy, stuck-on papules and plaques. They begin to appear in middle-age and increase in number with age.
- SKs are typically multiple and can appear on any skin surface except the palms and soles. A variety of colors are possible but generally SKs are light to dark brown. They are sharply demarcated, waxy, classically described as "stuck-on" papules or plaques, often with a smooth or slightly scaling surface.
- Histologically, SKs appear as a thickened acanthotic epidermis with impressive hyperkeratosis to the point of forming keratinzed cysts and pseudo-cysts within the epidermis. Increased pigment deposition is responsible for their potentially dark color.
- SKs are highly common and are frequently encountered in the elderly. Their number can increase with age and individual lesions can grow in area. Other than cosmesis SKs themselves are harmless; however, they can be occasionally confused with melanoma. As an interesting side note, a sudden eruption of a large number of SKs can be an indication of internal malignancy, known as the sign of "Leser-Trelat".