One of the most important functions of our skin is to help our body retain moisture. That requires an intact moisture barrier, which means surface cells must fit together in a very neat and efficient manner. With time and sun exposure, these cells generally don't fit together so well and we tend to lose moisture to the environment. Consequently, skin becomes dehydrated, and feels tight and uncomfortable.

"Dry" means lacking moisture, not wet, implying the surface may never have been wet. "Dehydrated" means that it was moist at one time but the water has been removed and it is now dry. Both words refer to the absence of water. In common usage, "dry" often means lack of oil, and "dehydrated" describes lack of water.

Dry air, wind, sun exposure, excessive cleansing, high altitude/low relative humidity, alcohol intake, fever, and smoking can all affect skin's moisture level. Insufficient water intake—especially after periods of heavy perspiration (exercise, summer heat) or illness—may also be a factor. Even oilier skins can become dehydrated if they don't receive sufficient hydration.

Some young people inherit their dry skin, but for most people, skin's barrier function—and its ability to retain moisture—gradually diminishes with age. Also, skin thins over time and oil production decreases. The effects of cumulative sun damage can further decrease barrier function.

Gently exfoliate. If we look closely at the surface of dry skin, there tends to be an accumulation of dead cells, which curl up and produce a dry, uncomfortable feeling on the skin. Removing or exfoliating these older, dead cells not only helps improve skin's appearance—it also helps restore barrier function and skin's ability to retain moisture. Skin that's exfoliated will feel more comfortable, and will be more able to withstand external irritants. Exfoliation also makes it easier for skin to absorb moisturizers and their beneficial ingredients.