Dry hair develops when your hair doesn’t get or retain enough moisture. This reduces its sheen and can make it appear frizzy and dull. Dry hair can affect men and women of any age, but you’re more likely to develop it as you get older. Your hair consists of three layers. If your hair is healthy, natural oils in the outer layer help protect the inner layers. They also reflect light, making your hair appear shiny. Sheen and luster are two important signs of healthy hair.