What is the skin barrier

The skin's natural protective barrier is also called a "brick wall structure."

In 1983, American scholar Elias PM proposed the famous "brick wall theory" of the skin's natural barrier.

The natural barrier of the skin refers to a "brick wall-like structure" composed of keratinocytes, "lipids" between cells, and NMF (natural moisturizing factor). The bricks are keratinocytes, and the mortar is the lipids between keratinocytes and substances such as NMF.

The outermost layer of the skin, the stratum corneum, and the "sebum film" covering its surface together form a natural protective barrier for the human body.

The sebum film is a transparent, weakly acidic film covering the surface of the skin, also known as the hydrolipid film. It does not belong to the skin structure, but it is closely related to the skin.

The sebum film is the outermost line of defense of the skin barrier. It is mainly composed of sebum secreted by sebaceous glands, sweat secreted by sweat glands, lipids produced by the disintegration of stratum corneum cells, and water emulsification, and is weakly acidic. Its main ingredients are ceramide, squalene, linoleic acid, linolenic acid and lipid components, which have the functions of locking in moisture and having certain anti-inflammatory effects.

The stratum corneum is located in the outermost layer of the epidermis. It is composed of 5-15 layers of keratinocytes and is 20-30um thick. The main components of lipids between keratinocytes are: 50% ceramide, 10-20% free fatty acids, and 25% cholesterol. The stratum corneum is the main pathway for skin absorption. A normal stratum corneum can resist external stimuli well and maintain the hydration function of cells. It is an important barrier for the skin!

Normal and abnormal skin barrier function

When the skin's natural barrier function is normal, moisture in the skin is not easily lost, and the skin is not easily dehydrated and dry; symbiotic bacteria such as bacteria, fungi or viruses on the skin's surface are not easy to cause disease; and the skin's absorption function is normal.

Once the skin barrier is damaged, transepidermal water loss increases, the skin's ability to retain water deteriorates, and the skin becomes prone to dryness, flaking, roughness, dullness, and paleness; the skin has poor resistance to external stimuli, and various symbiotic bacteria can easily enter the dermis and trigger an immune inflammatory response; the skin's blood vessels and nerve endings are prone to uncomfortable symptoms such as fever, itching, and tingling when stimulated by external stimuli.