Actinic keratosis, a common skin condition, can cause crusty brown spots on skin, typically called age spots or sun spots, according to Healthline. The scaly spots develop when keratinocytes, which are skin cells, begin growing abnormally. The patches of discolored skin may also be pink, grey or tan.
Actinic keratoses is the correct name for the spots, which develop in people who have intense exposure to sunlight over long periods of time. The spots appear with age, usually on the arms, hands, face, neck and scalp. Most of the time, the spots are benign, but there is about a 10 percent chance that one or more of the lesions may develop into squamous cell carcinoma, a common skin cancer. Patients need to monitor the spots, and if changes occur, such as bleeding, inflammation or rapid growth, they need to see dermatologists, notes Healthline.