The stratum corneum, also called the horny layer, is part of the epidermis of the skin. It performs various protective, resistance, hydration and permeability functions.
It is also the layer of the skin where the pores of the sweat glands and the openings of the sebaceous glands are seated.
It is the outermost layer of the skin and is found on top of the deeper layers of the skin, such as the stratum germinativum and stratum basale. It is composed mainly of cells called keratinocytes, which produce keratin, a hard, tough protein that protects the skin from dehydration, infection and other damage.
What is the stratum corneum
The outer layer of the epidermis, the one you see and can touch, is called the stratum corneum. It is formed by keratinized cells without nucleus, called corneocytes. They are located one on top of the other, joined by keratohyalin. These cells are flat and thin, die and fall off the skin during desquamation.
The stratum corneum also contains lipids that are found between the cells of the layer and help maintain the skin’s hydration and protect it from water loss. In addition, it acts as a physical barrier that prevents the entry of pathogens and other harmful agents into the body. It is thicker in the hands and feet.
The human stratum corneum comprises about 15 layers of flattened corneocytes and is divided into two layers: the stratum compactum and the stratum disjunctivum. The compact stratum is the deep, dense and cohesive layer, while the disjunctive stratum is looser and lies superficial to the compact stratum. As the disjunctive stratum continues to lose adhesiveness due to decreased adhesion between corneocytes, the cells desquamate.
Functions of the stratum corneum
The main function of the stratum corneum is to protect the skin from infections, dehydration, chemicals and mechanical stress. It acts as a barrier by functioning as a complex intelligent system that keeps the skin tissue properly hydrated, thus preventing skin cracking.
How does it do it? According to several studies, it maintains an average level of hydration to avoid dehydration or excess water, which could lead to increased permeability and thus to a decrease in skin protection.
The two components of the stratum corneum, the extracellular lipid matrix and the corneocytes, have different functions:
- Corneocytes provide mechanical reinforcement, protect underlying mitotically active cells from ultraviolet (UV) damage, regulate the onset of cytokine-mediated inflammation and maintain hydration.
- The extracellular lipid matrix that creates the brick-and-mortar organization of the stratum corneum regulates permeability.
Desquamation is the most common clinical evidence of disease in the stratum corneum. It represents inadequate or defective keratinization and desquamation.
Diseases characterized by desquamation are dermatitis (eczema), psoriasis and ichthyosis.
The stratum corneum is a very important layer of the skin and its function is fundamental to the health and well-being of the skin. It is constantly being renewed and is renewed approximately every 28 days.