What is the Epidermis?

The epidermis is the outermost layer of your skin. It protects the body from pathogens, keeps the skin hydrated and determines skin color.


The epidermis contains column-shaped basal cells that are constantly dividing and being pushed toward the surface of the skin. It also contains melanocytes that produce melanin, which gives skin its natural color.송도피부과

Basal Layer

The basal cell layer (also called the stratum basale or stratum germinativum) is the first epidermal layer. It contains a single layer of skin cells that continually divide and force older, dead cells up toward the surface where they are eventually shed.

The keratinocytes in this layer produce the protein keratin, which forms hair, nails and your skin’s outermost layer. They also produce melanocytes (mel-an-o-site) that produce the pigment melanin, which determines your skin’s color. Melanocytes package melanin into tiny parcels called ‘pigment packages’ that are transferred to the keratinocytes for processing.

The squamous cell layer (also called the stratum spinosum or prickle cell layer) is located just above the basal cell layer. The keratinocytes in this cell have accumulated so much keratin that they become tough, flat and translucent. They also have lots of desmosomes, which are cell-to-cell connections that resemble spikes, giving this layer its ‘prickle’ appearance.

Stratum Basale

Stratum basale, also known as the germinativum layer, is the innermost epidermis cell layer. It consists of a single layer of tall, simple columnar epithelial cells. These cells, or keratinocytes, rapidly divide to replenish the regular shedding of skin from the surface. They form the protective barrier against water loss and physical damage.송도피부과

The cells in this layer produce a protein called keratin that makes up the tough, waterproof outermost skin layer. They also secrete defensins, which are our first line of defense against infection and other threats to the skin.

Melanocytes in the epidermis produce melanin, a dark pigment that gives your skin its color. They transfer melanosomes to keratinocytes in the stratum spinosum layer, where they are absorbed by the keratin and help shield skin from harmful UV rays. The cells in the stratum lucidum are a translucent, seemingly transparent layer of dead and flattened keratinocytes that provide an efficient barrier to water.

Stratum Spinosum

The next layer up, the stratum spinosum, contains cuboidal to columnar mitotically active stem cells that produce keratinocytes. These keratinocytes, also known as corneocytes (corn-ee-o-site) and granulocytes (gra-nu-lo-site), are characterized by a prickle appearance that is a result of their protruding cell processes called desmosomes (dez-mo-so-me’s). The stratum spinosum also contains melanocytes, cells that produce the pigment primarily responsible for giving skin its color.

The cells in the stratum granulosum, which are flattened and stick together, form a barrier that protects your underlying tissues from microbes, dehydration and other environmental stresses. This is why the skin on your hands and feet appear thicker than that on other parts of your body.

The stratum granulosum is followed by the stratum corneum, which you can see as the tough, translucent layer on your skin’s surface. The dead keratinocytes in this layer are densely packed with a clear protein rich in lipids — eliiden (ell-ih-den) — that gives the skin its translucent appearance and prevents water from easily entering or leaving the epidermis.

Stratum Granulosum

This layer is a flattened sheet of cells adjacent to the stratum basale, and contains granules. These granules, which contain neutral lipids, are thought to provide a barrier against penetration through the epidermis. Cells in the granulosum are also distinct from those in the stratum spinosum because they have bundles of tonofilaments, which are part of the cytoskeleton and give them strength.

As they move toward the surface, these cells become keratinized and begin to flatten. They then fuse with each other and release granules of keratohyalin, which are thought to help bind the keratinized granules to each other.

This process is called keratinization and is the key to the formation of the skin’s five layers. The epidermis of most of the body’s skin, which is called thin skin, consists of four different layers, including the stratum granulosum, stratum spinosum, and the stratum corneum. The skin of the palms and soles of the feet, which is called thick skin, has an additional fifth layer called the stratum lucidum.

Stratum Corneum

The stratum corneum is a layer of hardened keratin. It makes up 90 per cent of the epidermis and forms the outer barrier that keeps out bacteria and toxins. It also contains some lipids. It is semi-permeable, allowing water and some fat-soluble substances to pass through while keeping other materials out. The cells in this layer are called squamous cells and form finger-like downgrowths that are sometimes seen as scales. Diseases characterized by scaling and defective desquamation of the stratum corneum include dermatitis (eczema, psoriasis) and the ichthyoses.

The squamous cells in the layer are held together by proteins called desmosomes. These structures are visible under a microscope. This layer varies in thickness, and it’s thickest on the palms and soles of the feet. It contains keratinocytes that secrete defensins, which are our first line of defense against pathogens. It also contains melanocytes (mel-ann-o-sites) that produce the pigment melanin that protects the skin from UV rays.

Stratum Lucidum

The outermost layer of the epidermis is the stratum corneum. It is 20-30 cells thick and contains a keratin-rich secretion that serves as a protective barrier. This outer layer provides mechanical protection against scratches and abrasions of the deeper, more delicate layers below it. It also helps to keep the skin hydrated and protected from pathogens.

Cells of the stratum spinosum have desmosomes connecting them to each other with a thick tuft of intermediate filaments called granules. These filaments make the cells appear to be spiked or prickled and give this layer its name of the prickle cell layer (stratum spinosum).

When a cell in this outermost layer is scratched, it becomes loose and flakes off. This is known as dandruff and people produce up to 40 pounds of the stuff in their lifetimes. This shedding is also an important way the body removes dead skin cells from the surface.