Natural Moisturizing Factors (NMF) and Surface Lipids
The most important substance for the suppleness of the skin is water. The water content of the upper horny layer is between 10 and 20 percent in young skin. Without natural moisturizing factors (i), this water would soon evaporate and the skin would become dry and cracked.
The skin’s moisture comes from water from deeper layers (transepidermal water (i)) and from normal perspiration. Various factors such as a lack of moisture-binding substances or extremely low humidity can lead to an increased loss of moisture to the environment. Especially prone to this are more exposed regions such as the face and hands. A distinction is made between active, glandular and passive extraglandular (i) or transepidermal water (i) loss.
NMF - substances with a special relationship to water
Some of the body´s own substances, the natural moisturizing factors (i) (NMF), are capable of retaining water in the horny layer. These substances with a special water binding capacity are derived from sweat and the sebaceous oils (e.g. urea (i)) as well as the cornification process (e.g. pyrrolidine carboxylic acid).
The lipids of the skin surface
The skin surface lipids are made up of the epidermal lipids and lipids from sebum - important for the hydrolipid film. Various fatty acids, especially those originating from sebum and only found on the skin surface, give the lipophilic portion of the hydrolipid film an antibacterial and fungicidal effect.