Tending to appear most often in fair-skinned elderly adults with a history of significant sun exposure; cutaneous horns begin to develop as a growth that extends from a red base on the skin in the shape of a funnel. It is made up of compacted keratin, which is the same protein fingernails and toenails are made of. It is a specialized type of actinic keratosis and the size and shape of the growth can vary significantly. However, the vast majority of cutaneous horns are only a few millimeters in length. Squamous cell carcinoma can be found at the base of the horn, which is why they are such a serious sign of skin cancer.