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The stratum corneum is the outer layer of the skin (epidermis). It serves as the primary barrier between the body and the environment.
The epidermis is made up of five layers:
- stratum basale: the deepest layer of epidermis, made up of cuboidal and columnar cells
- stratum spinosum: made up of skin cells that are connected by desmosomes giving these cells a spiny appearance under a microscope
- stratum granulosum: made up of skin cells with granules containing components that contribute to the formation of the outer skin layer
- stratum lucidum: thin, lighter appearing layer only present on the palms and soles
- stratum corneum: the outermost layer of skin, made up of layers of very resilient and specialized skin cells and keratin
The stratum corneum consists of a series of layers of specialized skin cells that are continuously shedding. It’s also called the horny layer, as the cells are tougher than most, like an animal’s horn. The stratum corneum exists to protect the inner layers of skin.
Most areas of the stratum corneum are about 20 layers of cells thick. Areas of skin like your eyelids can be thinner, while other layers such as your hands and heels may be thicker.
Your skin is the biggest organ system in your body. The most important function of the skin is to protect the body from things in the environment that may cause harm.
The skin helps to
- keep your body temperature at a healthy level
- prevent water loss or absorption
The stratum corneum is sometimes described as a brick wall. The corneocytes that make up the cell envelope are layers, like bricks, mortared together by lipids, that create the outer water barrier.
If everything is working properly in the stratum corneum, the skin layer will help defend you against:
At the same time, it’s protecting the skin layers underneath.
Unfortunately, some of the products that you use to clean your body can harm the stratum corneum.
Surfactants, such as hand soap, will bind to the proteins in the skin and allow water loss through the skin and weaken the barrier created.
Using sensitive soap, such as an unscented bar soap, and not over-washing is suggested. Using moisturizers can also help to prevent your skin from drying out as well.
Parts of the stratum corneum
The stratum corneum is made up of many parts to help protect your lower skin layers. Although the structure could be described in vastly greater detail, for ease of basic understanding, you can focus on three primary categories.
The bricks, also called corneocytes, are mostly made up of keratin. Keratin is a protein also found in hair and nails.
Keratinocytes are created in the lower layers of the epidermis and operate with a phospholipid cell membrane, which can be quite permeable. When the keratinocytes are pushed to the stratum corneum, they’re transformed into corneocytes with a more durable cell envelope.
A healthy stratum corneum will shed approximately one layer of corneocytes each day. The corneocytes will then be replaced with new keratinocytes from a lower layer of the epidermis called the stratum granulosum.
The desmosomes serve to connect the bricks by joining the corneocytes together. These are formed via connections of proteins such as corneodesmosin.
In order for the bricks to shed at a healthy rate, enzymes must dissolve the desmosomes.
The mortar that secures everything in place is made out of lipids that have been released from tiny lamellar bodies that are present in the stratum granulosum. The lipids float into the space between the bricks and between the layers of corneocytes.
The mortar is very important in protecting the lower layers of the skin. It creates the barrier that keeps out bacteria and toxins.
The mortar and whole of the stratum corneum are slightly acidic due to cellular processes that work to produce the lipids. The stratum corneum has a pH of around 4 to 5.5. The acidity helps to prevent bacteria growth.
The stratum corneum is the outer layer of your epidermis (skin). It’s made up of mostly keratin and lipids. The visible cells shed and are replaced from the lower epidermal layers.
The cells have a 2-week cycle in the stratum corneum. When a keratinocyte enters the stratum corneum, it’s changed into a corneocyte and shed within a 2-week period.
If you’re concerned about your stratum corneum or general skin health, talk with your doctor about a skin care regimen that will help your skin’s mortar and bricks stay intact.