Natural moisturizing factors (NMF) is a collective name for a group of ingredients or molecules such as amino acids, lactate, urea, PCA and etc. NMF is mainly located in skin’s stratum corneum layer and its function is to retain sufficient moisture to the skin layer. Sufficient moisture in stratum corneum is important because it helps in:
- maintaining elasticity of the skin, protecting it from damage
- allowing hydrolytic enzymes to function in the process of desquamation
- contributing to optimum stratum corneum barrier function
Approximately one-third of water contained within the stratum corneum is bound, with the remainder being free water. Increasing the level of free water has no effect on the elasticity of the stratum corneum. Therefore, it is the NMF-bound water that gives the skin with its elastic qualities. Replacing or replenishing the supply of the NMF in the skin through the external application of moisturizers containing NMF appears to be a successful approach for the treatment of xerotic or dehydrated skin.
How NMF helps in fine lines and wrinkles?
NMFs are highly efficient in attracting and binding water from the atmosphere, and drawing it into the corneocytes. The hydrates NMF forms ionic interactions with keratin fibers, reducing the intermolecular forces between the fibers and thus increasing the elasticity if the stratum corneum and the skin ultimately. This elasticity makes the skin appear healthy and supple and prevent cracking or flaking due to mechanical stress. Furthermore, NMF allows the corneocyte cells to balance the osmotic pressure exerted by the intracellular “cement” surrounding them. By maintaining the osmotic pressure balance, it prevent excessive water influx, as seen in wrinkled skin of someone who has been in the bath too long, or water efflux, which would cause the corneocytes to shrink (as seen visibly as wrinkles or fine lines).
How NMF helps dry skin and dehydrated skin?
There are numerous enzymes function in the stratum corneum and they need liquid water to function properly. Many of these enzymes are involved in the process of desquamation, breaking the various bonds and forces holding the corneocytes together in the most superficial layers of skin. NMF water binding provides much of this necessary water. Reductions or the lack of NMF have been correlated with various stratum corneum abnormalities that manifest clinically as areas of dry skin with scaling, flaking, or even fissuring and cracking. All of these conditions show characteristics of abnormal desquamation, with the accumulation of corneocytes resulting in the visible dryness, roughness, scaling, and flaking properties of dry skin.
How is NMF formed?
NMF components are breakdown products from the proteolysis of the filaggrin protein. The conversion of filaggrin to NMF occurs as the corneocytes are moving to the more superficial layers of the stratum corneum. The timing and exact location in the stratum corneum of filaggrin processing is dependent on the water activity within the corneocyte and the external relative humidity. In a humid environment, the hydrolysis of filaggrin occurs almost at the outermost surface. While in low humidity, the proteolysis occurs at deeper layers where the NMF works to prevent dehydration of the skin.
Conversion of filaggrin to NMF is also controlled by the water activity within the corneocytes, and only occurs within a narrow range—if the water activity is too high, the filaggrin is stable, while if it is too low, the hydrolytic enzymes will be unable to function and degrade the filaggrin.15 Thus, the skin’s hydration status influences the degradation process of filaggrin.
It should also be noted that the creation of NMF creates high osmotic pressure from within the corneocyte. Therefore, the degradation process does not occur until the corneocytes have matured and strengthened and moved toward the more superficial layers of the stratum corneum, where the surrounding lipids and other extracellular components balance this osmotic pressure.
What will affects and reduces NMF level in skin?
- Routine washing with harsh cleanser will remove the NMF from the superficial layers of the stratum corneum.
- Exposure to UV.
- Aging process
- Loss-of-function mutations in the filaggrin gene (FLG)
- Exposure to low humidity environment
Source: Fowler, J. (2012). Understanding the Role of Natural Moisturizing Factor in Skin Hydration. Practical Dermatology. Retrieved from http://practicaldermatology.com/2012/07/understanding-the-role-of-natural-moisturizing-factor-in-skin-hydration