Client restrictions apply, please speak to your account manager for details. Seborrheic keratosis. This skin growth, also known as a seborrheic wart, is caused by overproduction of keratin, the tough fibrous protein found in hair and the outer layer of skin. Keratoses range from flat, dark brown rough patches, to small, wart-like protrusions covered with a greasy, removable crust. They are mainly found on the trunk and usually occur in elderly patients. They are harmless, but as they are unsightly can be removed by cryosurgery (destruction of tissue using extreme cold) or surgical excision.