THE SKIN BARRIER 

The skin barrier is formed on the stratum corneum which is the outermost layer of our skin. It is a barrier that protects our skin by preventing the loss of moisture and electrolytes which are essential to the skin while at the same time inhibiting harmful pathogens to enter inside your skin.

The skin barrier of the stratum corneum has a brick wall-like structure that looks like it has been built with cement.

Keratinocytes forming the skin barrier of the stratum corneum are enucleate keratinized cells and have natural moisturizing factors. The lipid components among the cells that connect the keratinocytes and other cells prevent moisture loss, and this is the reason why the skin barrier is also referred to as a bricks and mortar model in English-speaking countries. 

NATURAL MOISTURIZING FACTORS INSIDE KERATINOCYTES 

Natural moisturizing factors (NMF) are uniquely found in keratinocytes. Mainly comprised of PCA, urocanic acid, and amino acids, NMF keeps the stratum corneum moisturized by attracting moisture. So, it is the ‘moisturizing storage’ present inside the stratum corneum.

Thanks to NMF, the stratum corneum can maintain a certain level of moisture even in a dry environment. The amount of NMF inside the skin is gradually reduced due to various kinds of factors. Around the age of 25, the amount of NMF inside your skin is lessened naturally or it is removed together with the NMF of the stratum corneum from double cleansing.

 

CORE OF THE SKIN BARRIER - CERAMIDE 

Lipids found between the keratinocytes of the skin barrier consist of ceramide, cholesterol, and fatty acid in a fixed ratio so that they function as an oil layer that blocks the moisture loss from the skin. Ceramide is commonly used as a moisturizing component to prevent moisture loss, and here’s the reason why. Because moisture is retained by the NMF inside the keratinocytes and moisture loss is prevented by lipids between the keratinocytes, it is possible to maintain fully moisturized skin if you have a healthy skin barrier.