While dry skin and dehydrated skin can share many of the same characteristics, such as tightness, roughness, flaking, scaling, redness and sensitivity, they are quite different skin concerns. Dry skin generally refers to skin lacking in oil. Dehydrated skin is skin lacking in moisture - it is not so much a skin type as a skin condition. Even oily and combination skin can be dehydrated. Dehydrated skin occurs when the protective uppermost layer of the skin, known as the stratum corneum, is lacking in moisture. Some of the signs of dehydrated skin to look out for are itchy skin, dullness, dark circles under the eyes and the increased appearance of wrinkles.