Layers of the Skin:  Stratum Corneum

The stratum corneum, also known as horny layer, is the top, outermost layer of the epidermis. The esthetician is primarily concerned with this layer. The stratum corneum is very thin, yet it is waterproof, permeable, regenerates itself, detoxifies the body, and responds to stimuli. Keratinocytes on the surface have hardened into corneocytes which are the waterproof, protective cells. The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment.

This layer is comprised dead cell remnants and are completely filled with keratin fibers. They are also referred to as cuticle. Keratin is a tough, water-repellant protein designed to impede the invasion of pathogens and viruses. It guards the underling tissue and is essential for the adhesion of sebum.

This layer is referred to as the horny layer because of these scale-like cells. Keratinocytes are continually shed from the skin in a process called desquamation. These cells are replaced by new cells coming to the surface from the lower stratums. This process of desquamation and replacement is known as cell turnover. The average adult cell turnover rate is every 28 days depending on a person’s age, lifestyle, and health.

The acid mantle are the cells and oils that combine to form a protective barrier layer on the stratum corneum. Stratum corneum cells are surrounded by bilayers of oil and water. Lipids of the cell membranes, such as phospholipids and essential fatty acids, determine the health of this protective barrier. In general, the stratum corneum has 15 to 30 layers of cells. The keratinocytes on the surface of the skin are also called squamous cells. The stratum corneum has a pH of around 4 to 5.5. The acidity helps to prevent bacteria growth.


Where moisture is concerned, the stratum corneum plays an essential role in the function, health and maintenance of skin an and is the principal barrier tissue preventing water loss and the final cellular chapter of epidermal differentiation.  The stratum corneum also contains the skin’s natural moisturizing factor (NMF) and is responsible for maintaining skin hydration. As the skin ages, and as a result of environmental insults, this natural barrier function becomes compromised, leading to dry and dehydrated skin.

The stratum corneum structure contains dead skin cells (corneocytes) that contain a complex combination of lactic acid, urea, salts and amino acids, collectively referred to as the skin’s natural moisturizing factor (NMF). It also contains a natural water binding barrier for the skin that is made up of ceramides, cholesterol and free fatty acids that organize themselves into layers.  The stratum corneum prevents TEWL (Trans Epidermal Water Loss) by the formation of a continuous matrix of highly organized lipid lamellae into which is embedded an extensive network of corneocytes.  f there is a breakdown in either with the formation of the corneocytes or in the barrier, skin loses its ability to hold onto moisture. 


There has been a lot of recent studies and research on corneotherapy and approaches and treatments regarding the stratum corneum.  Corneotherapy treatment is centered on recovery of the stratum corneum. The stratum corneum is very complex even if it consists of cells not capable of dividing and multiplying, it is far from being static tissue. A key principle of Corneotherapy is to keep the epidermis intact at all times.  This approach of retaining the integrity of the epidermis ensures the skins defense and immune systems are not stimulated unnecessarily.

The principles of Corneotherapy can also be applied for the correction of skin conditions, and for the supportive prevention of skin problems and the prevention of premature skin aging.  This therapy is centered around the science of corneobiology, which is focused on the anatomy, physiology and biology of the stratum corneum. Corneobiology encompasses disciplines including immunology, endocrinology and psychology.

Corneotherapy can also be an individualized approach to skin care and treatment.  A skin therapist investigates and defines the causes of the conditions before selecting appropriate treatments, therapies or modalities that will achieve the best outcome. This contrasts with the more simplistic approach of treating symptoms without determining the causes.