Keratosis is the term for a family of skin conditions characterized by patches of thick, scaly skin. It is commonly caused by a vitamin deficiency in Vitamin A, but can also be caused by a deficiency in Vitamin D, Vitamin C, or Vitamin E. Vitamin A deficiency can lead to dry, scaly skin, while Vitamin D deficiency can cause redness and inflammation. Vitamin C deficiency can cause rough, discolored skin, and Vitamin E deficiency can cause brittle nails and thinning hair. Therefore, if you are experiencing the symptoms of keratosis, it is important to speak to your doctor about possible vitamin deficiencies.