SKIN STRUCTURE

To understand exactly how beauty products work, why common skin problems occur and what happens to our skin as it ages, it is important to have a basic understanding of normal skin structure and its constituent components.

The skin has two main parts: the upper epidermis and the lower dermis. These together sit on top of a layer of fat and connective tissue that gives the skin its support. The outermost layer of the skin – the upper part of the epidermis – is known as the stratum corneum. This is made up of dead skin cells that are integral to the skin’s function as a barrier. Skin cells turn over approximately every twenty-eight days, with cells from the upper layers being continually shed and replaced by cells from deeper layers.


## The epidermis

The epidermis is the outermost part of the skin, the bit that gets up close and personal with the outside world. To do its job successfully as the first line of defence, it has four main cell types, each with its own important role to play.

### a) Keratinocytes

The main cell in the epidermis, keratinocytes produce the protein keratin, which provides the skin with physical protection and waterproofing. You may already be familiar with keratin as it’s also the main component of hair and nails, and can also be an ingredient in some personal-care products.

### b) Melanocytes

These cells produce the pigment melanin, which gives our skin its colour and protects us against UV light from the sun.

### c) Langerhans cells

Langerhans cells are part of the immune system and are ready to seek and destroy any microbes that may invade the skin.

### d) Merkel cells

These sensory cells are found deep in the epidermis, and provide us with the sensation of touch.

## The dermis

The dermis sits below the epidermis. It is often divided into two layers: the upper ‘papillary’ dermis and the lower ‘reticular’ dermis. The papillary dermis is rich in nerve endings whilst the reticular dermis provides the skin with its structural support and elasticity, and is rich in collagen, elastin and hyaluronic acid. The beauty industry and anti-ageing market has taken much interest in these molecules, and as the terms are often thrown about in writing and talk on skincare, they definitely warrant a closer look.

### a) Collagen

Collagen is one of the most abundant proteins in the body. It forms a scaffold that gives strength, rigidity and support to the skin. There are at least sixteen different types of collagen in the skin, although 80 to 90 per cent of human collagen is of types 1, 2 and 3. Gram for gram, collagen is stronger than steel.

### b) Elastin

Elastin is another connective tissue protein found in skin. As its name suggests, elastin gives skin its elasticity; indeed, its properties are often compared to those of elastic bands: it allows skin to resume its original shape after being stretched, pinched or poked.

### c) Hyaluronic acid

Hyaluronic acid belongs to a group of compounds known as glycosaminoglycans, and also forms part of the skin’s framework. It is essentially a very large sugar molecule with a gel-like consistency. Hyaluronic acid has a unique capacity to bind over 1,000 times its own weight in water. Its purpose in skin is to keep it soft, plump and hydrated. Hyaluronic acid is a popular constituent in skincare due to its moisturizing properties; it can also be injected into, or under, the skin in the form of dermal fillers.