When skin lacks what component, it is classified as a dry skin type?

Dry skin type is classified as such when there is a deficiency of oil in the skin. The skin produces natural oils, known as sebum, which play a crucial role in maintaining moisture levels, protecting against external harmful elements, and providing a barrier that prevents excessive water loss. When there is insufficient oil, the skin loses its ability to retain moisture, leading to a dry and flaky appearance.

While hydration, water, and collagen are all important components of skin health, the primary characteristic that defines dry skin is the lack of oil. Hydration and water relate more to moisture content, and collagen is primarily concerned with the skin's structural integrity and elasticity. However, it is the deficiency of oil that directly affects the skin’s ability to appear smooth and well-moisturized, thereby classifying it as dry.