An important characteristic of moisture-deficient skin is a low water content. When the water content of the horny layer falls below 8 to 10 percent it becomes dry, rough and cracked. Because of its exposed position, facial skin loses more moisture than skin in other areas.
The horny skin layer is hydrated by water from deeper skin layers (transepidermal water (i) loss) and normal perspiration. If the skin is deficient in natural moisturizing factors (i) (NMF’s) or subjected to extreme weather conditions, it loses moisture, becoming dry and taut, and almost unable to absorb rich creams.
When the body’s own supply of moisture and natural moisturizing factors (i) (NMF's) is no longer sufficient, the skin becomes less supple and its protective function is impaired: The skin becomes dry and cracked and can no longer perform its barrier function properly. It becomes more susceptible to external influences and shows an increased transepidermal water (i) loss. Therefore moisture-deficient skin is in particular need of care that supplies not only moisture but also natural moisturizing factors (i) like amino acids. These hygroscopic substances, in a suitable formulation, bring about long-lasting skin hydration.
Weather conditions influence the skin's moisture loss. In dry, hot summer air it loses moisture very quickly. High humidity and low winds lead to a slower rate of water loss.