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Bearing in mind just how important the skin is, it should come as no surprise to learn that this organ is not a shapeless mass of cells but has a complicated structure. The skin consists of two main layers; the outer one is the epidermis and the inner one is the dermis. The main function of the epidermis is to form a tough barrier against the outside world, while the dermis is a soft, thick cushion of connective tissue that lies directly below the epidermis and largely determines the way the skin looks. Both layers are constantly repairing and renewing themselves, but the dermis does so more slowly than the epidermis. Under the dermis is a layer of fat cells, known as adipose tissue or subcutaneous (below the skin) fat, which provides insulation and protective padding as well as a store of energy.

Just as the thickness of the skin varies slightly throughout the body, so does the structure. For example, you do not find hairs on the palms of the hands or the soles of the feet. Generally, though, the skin is pretty similar all over the body. If you examine the skin in more detail you can see what an amazing job it does.

The epidermis

The epidermis is sub-divided into four distinct layers: the basal, spinous, granular, and cornified layers.

Basal layer: Cells here are attached to the basement membrane, which separates the epidermis from the dermis. Basal cells continually divide and grow to produce new cells that gradually move up through the epidermal layers to the surface. The basal layer also contains special cells, called melanocytes, that produce the pigment melanin. Melanin not only acts as a sunscreen against ultraviolet light but it also determines normal skin color, being naturally more prevalent in darker-skinned people.

Spinous layer: Here, cells rising up from the basal layer start to flatten out and produce a tough protein, keratin, to protect the body from harm.

Granular layer: In this layer, the still-living cells continue to flatten and fill with keratin but then gradually lose their nuclei to become dead cells.

Cornified layer: This is the outermost layer of the epidermis where the scale-like cells are made up almost entirely of keratin. These cells are all dead and are constantly being worn away and replaced by cells from below.

The dermis

The dermis is thicker than the epidermis. It consists mainly of connective tissue, which is made up of fibers of the proteins collagen and elastin and a non-fibrous gelatin-like material called ground substance or extracellular matrix (ECM) that fills spaces between the fibers. Moving through the matrix and among the fibers are fibroblast cells that manufacture the protein fibers and weave them together to form a web-like structure. These fibers often occur in bundles, made up of many fibrils lying parallel to one another, and they are very strong. They are found in all types of connective tissue such as bone, cartilage, tendon, and ligament.

The dermis contains blood vessels, which supply oxygen and nutrients to the skin and remove waste products, as well as special skin structures such as sensory receptors, nerve endings, sweat glands, and hair follicles – the deep pits that house the hairs. Each hair grows from the papilla, an area at the bottom of the follicle. Like skin, hair is made up mostly of keratin and is dead, except at its base, where new hair is constantly being formed. Each hair grows for about four years and then falls out and a new period of hair growth begins. Each follicle is surrounded by nerve endings that respond to the movement of the hair and can detect, for example, a light touch or a gentle breeze.