There are many possible causes of dull, dry skin. One common cause is dehydration. When the body is not adequately hydrated, the skin can become dry and lackluster. In addition, cold weather can lead to dry skin, as the low humidity levels strip away moisture. Another common cause of dull skin is a build-up of dead skin cells. As our skin cells die, they can accumulate on the skin's surface, creating a barrier that prevents moisture from getting in. Excess exposure to sunlight can also cause the skin to become dried out and restless. If you are concerned about your dry skin, it is best to consult with a professional to find out the underlying cause and get specific treatment recommendations.