Skin lesion. Light micrograph of a section through a seborrheic wart. Also known as keratoses, these raised skin lesions develop in the elderly. They are not true warts, but are caused by a proliferation of basal cells in the skin, and are often pigmented. Melanocyte cells that contain the pigment melanin are seen (brown). The lesions are often raised on a central stalk, and therefore are subjected to trauma, which may cause them to bleed and become irritated. Although they are benign many people have seborrheic ketoses removed for cosmetic reasons.