Abnormal growth of keratin on the skin and mucous membranes is called keratosis. Actinic keratosis, hydrocarbon keratosis, keratosis pilaris and seborrheic keratosis are all different types of keratosis. Presence of patches of thick and scaly skin is actinic keratosis. Exposure to polycyclic aromatic hydrocarbons causes cancerous skin lesions which is known as hydrocarbon keratosis. Presence of benign skin tumor is seborrheic keratosis. An autosomal dominant, genetic disorder that cause red bumps on the skin is keratosis pilaris.