In healthy skin, there is a normal physiological balance between the production of new cells and the shedding of the old ones. The outmost layer of skin, the stratum corneum, is approximately 20 layers of non-living, yet functional, cells called corneocytes. They are held together by protein bridges called desmosomes. Desquamation is the process by which these protein bridges are enzymatically dissolved allowing the shedding of the most superficial cells. The enzymes responsible for dissolving these bridges can only function in a well hydrated environment. When the water content in the outer layer of skin decreases, these enzymes become ineffective and can not dissolve the desmosomes. The retention of these most superficial cells makes the skin look dry and scaly.
Quality moisturizers help increase the water content of the outer layer of skin increasing the activity of the enzymes that break the protein bridge connections between corneocytes. This allows for appropriate shedding of old superficial skin cells resulting in soft smooth hydrated skin.