Stratum Corneum

by | Aug 18, 2020

The outermost layer of the skin structure is the stratum corneum. The stratum corneum and the sebum membrane together form the skin barrier.

Many people have a deep misunderstanding of the stratum corneum under the promotion of advertisements. They think that the stratum corneum is a pile of dead cells that hinder the regeneration of the skin. But in fact, the stratum corneum is an indispensable good thing for us.

The stratum corneum is the front-line barrier between the human body and the external environment. It has long been thought that the stratum corneum has no biological activity. But with the development of science and technology, scientists have found that the stratum corneum is highly active and plays a key role in maintaining the stable state of the human skin barrier.

Stratum Corneum Overview

  • The stratum corneum is composed of a brick wall structure: bricks—keratinocytes; cement—intercellular lipids.
  • Keratinocytes contain the famous natural Moisturizing Factor (NMF)
  • Half of the intercellular lipids are ceramide (Famous active ingredients in skin care products)
  • Keratinocytes of the skin are updated every 28 days.
  • Stratum corneum care: Reasonably clean, use products containing repair ingredients.

Stratum Corneum Definition

As we said in the skin structure, the stratum corneum structure is similar to the typical brick wall structure. Keratinocytes are bricks, and intercellular lipids are cement.

Such a structure also allows the stratum corneum to have the function of a wall, silently protecting our bodies from the wind and sun.

The structure of the stratum corneum: its surface is covered with a layer of sebum and its interior consists of a brick wall structure of keratinocytes, which are filled with intercellular lipids.

In the following, the keratinocytes and intercellular lipids will be introduced respectively.


As a brick of the stratum corneum, the shape of the brick is a flat polyhedron. Keratinocytes contain a lot of natural moisturizing factor(Composed of amino acids, pyrrolidone carboxylic acid, and lactate).

The natural moisturizing factor (NMF) is extremely water-absorbent and can control the evaporation of water, thereby controlling the skin’s moisture content to maintain a normal state.

Because NMF has the excellent moisturizing ability, major cosmetics companies are rushing to study. For example: The Ordinary, Medicare, and other brands have launched NMF moisturizing products.

Intercellular lipids:

Made of 50% ceramide, 15% cholesterol, 5% cholesterol esters, and 30% free fatty acids.

These several components can form a very delicate lipid bilayer structure. Such a structure is filled between keratinocytes, which can effectively prevent the loss of water, nutrients, and electrolytes in the body, and has a deep moisturizing effect.

The bi-molecular structure of intercellular lipids. One end of the structure is a ball, and the other end is a thin strip.

Lipid bilayer structure

The reduction of any substance in intercellular lipids will cause corresponding skin symptoms.

The reduction in ceramide will cause dry skin, desquamation, atopic dermatitis, and eczema.

The reduction in free fatty acids will cause psoriasis.

The reduction in cholesterol will cause skin aging and photoaging.

Stratum Corneum Metabolism

The keratinocytes in the stratum corneum have been iteratively updated, new ones appear and old ones fall off. Inadvertently, you have changed your face.

Keratinocytes are born from the deepest basal corneum of the epidermis, and these newborns migrate upward to replace the upper layer of cells. The upper cells will leave the skin surface.

From birth to maturity, to the function that the stratum corneum cells should have, to service, and finally to fall off. The life of keratinocytes will last a total of 28 days.

The differentiation process of cells. Newborn cells are produced from the stratum basale and gradually migrate upward to the stratum corneum. The migration process takes about 14 days. Keratinocytes and intercellular lipids form the stratum corneum, which is finally shed from the skin. This process takes about 14 days.

Keratinocytes: from birth to death

Every cell in your body interprets this proposition at all times: stick to the responsibility given to you by life, live calmly, and face death calmly.

The life of keratinocytes is quite exciting, we divide it into two stages:

The first stage: the growth phase of keratinocytes

After the keratinocytes are born in the stratum basale, they enter the growth phase. In this stage, the new cells will continue to migrate upwards to the stratum corneum.

During the migration process, the new cells will bring melanin, a strategic weapon produced by melanocytes, to resist the attack of ultraviolet rays.

At the same time, the new cells form a small capsule in the body containing something called a lipid. The entire migration process took 14 days.

The second stage: the service period of keratinocytes

After the new keratinocytes reach the stratum corneum, they enter the service period. At this time, the keratinocytes found that the moisture in the environment had been greatly reduced. They found that the environment in which they lived has changed significantly. So they are tightly linked to each other, and at the same time spit out the internal lipids to the outside of the cell, And then degrade the keratin inside the cell into natural moisturizing factor(Composed of amino acids, pyrrolidone carboxylic acid, and lactate).

In this way, keratinocytes together with its digestate and excrement form a strong brick wall structure. The entire service period also took 14 days.

Eventually, keratinocytes will shed, ending their life.

As we grow older, this exfoliation process will start to become slow. Some dead cells that should have been exfoliated have not left our skin. If our skin barrier is intact, we can use some gentle exfoliation methods to remove excess keratin.

Stratum Corneum Function

stratum corneum cells, intercellular lipids, and the sebum membrane covering the skin surface, these three constitute the outermost protective layer of the skin, commonly known as the skin barrier.

The skin barrier locks in moisture and oil to help protect the skin from various germs. A healthy skin barrier can help reduce the occurrence of skin diseases and slow down the aging process.

The consequences of destroying the skin barrier are very serious: such as sensitive skin, lack of water in the skin, skin irritation, melasma, bacterial fungal infections, etc.

The picture on the left is a healthy skin barrier. Its stratum corneum is intact and can prevent the loss of body water and damage from external stimuli. The picture on the right is an unhealthy skin barrier. Its epidermis is damaged, the water in the body is easily lost, and the outside is easy to damage the inside of the skin.

Sebum And Stratum Corneum

The sebum membrane is mainly composed of the sebum secreted by the sebaceous glands, the lipids produced by keratinocytes and the sweat secreted by the sweat glands. The sebum membrane contains wax fat, triglyceride, free fatty acid, ceramide, squalane, and other substances. It is also mixed with phospholipids and cholesterol lipids produced after epithelial cell metabolism.

The sebaceous membrane is closely related to the stratum corneum, which can be described as a interedependency. Some people may not understand the difference between the damage of the sebaceous membrane and the stratum corneum. The difference between the two is quite large, mainly reflected in the degree of damage to the skin condition.

Damage to the sebaceous membrane is the initial state of damage to the stratum corneum, and the stratum corneum begins to be damaged when the sebaceous membrane is damaged. So, if you want to repair the stratum corneum, first repair your sebum film.

Only after the sebaceous membrane is rebuilt, the stratum corneum begins to renew and thicken. The skin is considered to return to a normal cycle. Looking at the picture below, you can know the progressive relationship between the two.

Detailed introduction of damaged stratum corneum and damaged sebum membrane. Dark orange describes the skin condition with damaged stratum corneum, and light orange describes the skin condition with damaged sebum membrane.

As can be seen from the above figure, our skin barrier damage covers damaged sebum membrane and damaged stratum corneum.

Here is a summary of several damaged features.

Damaged sebum membrane

  1. There is a sense of tightness after washing the face, the skin is getting dry.
  2. The surface of the skin is rough, and the moisturizing function is weakened.
  3. There will be a tingling sensation when using masks and other skin care products.

Damaged stratum corneum

  1. The skin is prone to redness, itching, and sensitivity.
  2. There is very obvious red blood on both sides of the cheek.
  3. The skin becomes very sensitive, and there are symptoms such as redness, dryness, tingling, and redness in the environment of excessive cold and heat.

How To Repair The Skin Barrier?

When the skin barrier is broken, there are two main ideas for repairing the barrier:

Reasonable cleaning and ingredient repair.

Reasonably clean

Girls with thin cuticles should never clean their skin excessively and do not use cleaning products that are too rich in soap.

Excessive cleaning will cause a large loss of sebum, which has a protective effect on the stratum corneum, thereby destroying the skin barrier. If there are no special needs, it is recommended to use a mild amino acid facial cleanser.

When the skin barrier is broken, try to avoid using the cleansing mask, scrub, fruit acid, salicylic acid, and other exfoliating products.

Ingredient Repair

The essence of ingredient repair is to directly or indirectly supplement ingredients similar to the stratum corneum, thereby simulating the environment of healthy skin.

The following components are common to the repair of the stratum corneum:


We know that 50% of the intercellular lipids are ceramides, so directly supplementing ceramides is an effective way to repair the stratum corneum.


Glycerin is a kind of very absorbent moisturizer, Can quickly help the stratum corneum restore water content.

Besides, glycerin can stimulate the skin to produce a channel protein that specifically transports water from the dermal layer to the epidermal layer, ensuring the normal function of the entire epidermal layer.

It can fundamentally improve the water-carrying capacity of the epidermis and lay a solid foundation for the repair of the stratum corneum.

Sodium pyrrolidone carboxylate (PCA-Na)

Sodium pyrrolidone carboxylate is one of the important ingredients of natural moisturizing factor (NMF) in keratinocytes. It has good hygroscopicity and helps repair the stratum corneum.

I hope that all the beautiful girls can polish their eyes, recognize some exaggerated publicity, take good care of their skin, and take care of our stratum corneum.