<unk>  is a premalignant condition of thick, scaly, or crusty patches of skin. It is  most common in fair-skinned people who are frequently exposed to the sun, because their pigment isn't very protective. It usually is accompanied by solar damage. Since some of these pre-cancers progress to squamous cell carcinoma, they should be treated.
Actinic keratosis
Inverted follicular keratosis
Nevus comedonicus
Lichen nitidus
Eccrine nevus
Porokeratosis
Actinic granuloma
White sponge nevus