Unmasking skin

If you look in the mirror, your skin looks like a simple covering for the body. In fact this is a deceptive image: consider that the skin is the largest living organ in the human body, as essential and hard working as the brain or heart, and the closest contact we have with the outside world. It's literally out last outpost, and usually the unsung hero. Besides its obvious role of keeping our insides in, skin is also responsible for keeping foreign inviters out, regulating body temperature, getting rid of waste matter, acting as a water reservoir, manufacturing vitamin D from sunlight and housing our senses of touch and pain.

From a distance, your skin appears smooth and flat, but on closer inspection you will see that a network of tiny grooves, which change shape as the skin moves, marks and surface. A cross section looks a little like a complex Dagwood sandwich, with various layers and fillings. The two skin layers - the epidermis and dermis - rest on a third layer of subcutaneous fat, and send signals to the brain to set various physiological functions in motion. In order to take the best care of your skin, it's important to understand how these layers work.


The EPIDERMIS

Your skin's front line of defence is the epidermis. It allows light to partially pass through it as it would through frosted glass, and is nourished by blood vessels in the deeper layers of the skin that provide it with oxygen and "skin food". Plump, moist skin cells are developed in the basal layer of the epidermis. As each new layer of skin cells form, the cells move up towards the skin's surface, becoming flattened as they do so. By the time they reach the outer horny layer of the skin - known as the stratum corneum - they are affectively dead. These layers of densely packed cells, known as corneocytes, are filled with a protein called keratin, and a fatty lipid. Like the tiles of a roof, they overlap in layers to form a strong, protective shield that prevents water loss. Throughout you life, the cells of the surface layers are continually being worn away and replaced with new cells from below. In normal skin, it takes about 30 days for the cells to move up to the surface. If the outer layer is being lost quickly - due to sunburn, for example - these cells will be replaced more swiftly.

Below the stratum corneum are the Langerhans cells, which patrol for invaders, and the melonocytes - cells that produce the pigment melanin, which helps determine the colour of your skin and hair. Melanocytes evolved to help the skin ward off dangerous UV radiation; the melanin on the skin surface adsorbs UV light, protecting the cells below. Within the melanocyte, melanin is packaged in small membrane sacs called the melanosomes. The difference in pigmentation of various ethnic groups is due to the way in which the pigment is packed in these melanosomes. Skin cells in black-skinned people do not contain more melanocyte cells, but the melanin granules are larger and individually dispersed. Black-skinned people, therefore, are genetically programmed to be more resistant to UV damage because of the profusion of melanin within their cells. People with white skin tend to suffer more from unprotected sun exposure because they have less melanin, and because their melanosomes are smaller and grouped together in membrane-bound clumps. Skin cells in Asian people contain smaller melanosome complexes that are more densely packed that those found in Caucasioan skin cells.

The DERMIS

The dermis is composed entirely of living cells. While the epidermis can repair itself, the dermis can become permanently damaged. This layer consists mainly of collagen, a protein that's responsible for the structural support (i.e. strength and resilience) of the skin. Collagen is packaged in bundles held together by elastic fibers. These are made up of another protein, elastin, which gives the skin its tone, plumpness and elasticity. Also found in the dermis are the sebaceous glands, hair follicles and sweat glands. The main function of sweat glands is to regulate the body's temperature. They are distributed over the entire body surface, with a larger number on the palms, soles and forehead. The sebaceous glands produce sebum (oil), the skin's natural lubricant. They are very sensitive to hormones, which increase the glands' size and the secretion of sebum. (that's why males are more prone to acne, especially during puberty.) Sebaceous glands therefore play a key role in determining facial skin type.

Do men and women age differently?

There is definitely a difference in male and female skin and so also in the ageing process. Women have less collagen than men to begin with, and because men have a thicker stratum corneum and produce more sebum than women, the lipid film on their skin surface is more pronounced. Furthermore, men's sebaceous glands are active well into their eighties. Also, testosterone, which is found in far higher levels in men, increases the rate of cell turnover in the basal layer and enhances collagen production, thereby thickening the skin. While there is a gradual thinning of skin with age in men (about 1% per year), the thickness of a woman's skin remains fairly consistent until menopause, when her oestrogen levels start to fall. Then she will experience a dramatic thinning of the skin, and decreased collagen synthesis and repair. In addition, there is an increase in intrinsic ageing with the failure of oestrogen production and reduced dermal hydration.