Keratosis (from kerat- + -osis) is a growth of keratin on the skin or on mucous membranes stemming from keratinocytes, the prominent cell type in the epidermis. More specifically, it can refer to: actinic keratosis (also known as solar keratosis), a premalignant condition chronic scar keratosis hydrocarbon keratosis keratosis pilaris (KP, also known as follicular keratosis) seborrheic keratosis, not premalignant.