Your hair consists of three layers. The cuticle, cortex and medulla. If your hair is healthy, natural oils in the outer layer (cuticle) help protect the inner layers. The cuticle layer if undamaged, reflects light, making your hair appear shiny. Sheen and lustre are two important signs of healthy hair.When your hair is dry or damaged, the outer layer breaks down, causing it to appear dull and unhealthy. A variety of factors can lead to dry, damaged and dull hair, including environmental conditions, hair care habits, and your physical health. Dry hair is definitely a sign that damage is occurring. If left untreated, your hair can become brittle, causing it to break or split. Most cases of dry or damaged hair can be effectively treated with simple lifestyle and hair care changes. Daily shampooing can rob, already dry and damaged hair, of its protective oils and lead to further dryness. Try washing your hair once or twice a week instead and make sure you use an appropriate shampoo that is gentle and hydrating. Always condition your hair after a shampoo, never skip this step. You can also apply a hair mask once a week or use a daily leave-in conditioner or hair oil to add lustre and softness. Protecting your hair from heat and sun exposure is also important. If you live in a dry climate, wear a hat when you go outdoors and avoid long-term exposure to dry or windy air. You should protect your hair from chlorine and salt water by applying a leave-in conditioner before you enter the water or by wearing a bathing cap.