What makes our skin the way it is?
Everyday we wash, buff and apply creams to our skin, but how much do we really know about the complex structure covering our bodies?
In simple terms, our skin is made up of three distinct layers: the top or outer layer called the epidermis; the second layer called the dermis, which contains blood vessels, nerve endings, hair roots and sweat glands; and finally the subcutaneous fat layer containing larger blood vessels and nerves.
We all appreciate that when our skin is dry it often feels rough and flaky. It's the top layer of the epidermis - the stratum corneum - that plays a key role in helping contain moisture within the skin. Normally up to 15% of the stratum corneum consists of water. When the moisture content of the stratum corneum falls below 10% the skin appears dry and flaky; further drying can lead to reduced flexibility and cracking.
The spaces between the cells in the epidermis are packed with fats, or lipids, and other components. A mixture of amino acids and salts, which are water soluble and present within the cells and help the cells hold in their moisture, is known as the "natural moisturising factor". This is important as it helps the stratum corneum regulate natural water loss by preventing water evaporating from deeper layers of the skin. The mixture of amino acids and salts are easily washed out (being water soluble), which reduces the ability of the cells at the surface to hold on to their moisture. Sometimes when we use strong soaps or detergents, or are exposed to solvents, these valuable components are washed out and the skin loses some of its ability to keep water, it then becomes dry and will start to crack.
Skin cells are constantly being renewed and the dead cells shed. The epidermis contains natural enzymes that are important for getting rid of old skin cells. These enzymes need moisture to work properly.
What does moisturiser consist of and how does it work?
Moisturiser can play a key role in both adding water to the skin and keeping it hydrated.
In terms of facial moisturisers, most are made up of oil-in-water emulsions consisting of tiny droplets of oil held in a watery base. To prevent the oil and water from separating or deteriorating, manufacturers add stabilising ingredients, such as emulsifiers and thickeners.
In order to help keep water in the skin, moisturisers contain substances called humectants. These are substances that are capable of attracting water and help to conserve the water in the skin. One of the oldest and best examples is glycerin, sometimes called glycerol. This has been the standard humectant for many decades based on its excellent safety record.
In the case of dry skin, the skin cells are being shed too fast. Rather than being shed individually these come off in clumps that look like white flakes. Repeated application of moisturiser increases the water content and normalises cell turnover. This is why it is important to continue using a moisturiser on the skin.
Because most cosmetic moisturising products have a water base they need preservatives, to stop them being contaminated by micro-organisms. These are everywhere in the environment as well as on and in our bodies. Without preservatives, micro-organisms would rapidly spoil the product, and even cause it to become a risk to health. So, what does a moisturiser basically consist of? A cosmetic moisturiser designed to encourage skin hydration will be made from water and humectants, blended with oils and emulsified to form a liquid or cream.
How can moisturisers make our skin look visibly better?
Adding moisturiser means that a liquid now fills the air gap between the dry skin flakes and the skin rather than just air, this liquid has a closer refractive index to that of skin and as such helps to transmit light rather than reflect it. With increasing moisture levels, the stratum corneum becomes more translucent and this means more light can reach the lower layers of the skin. This is responsible for the apparent enhancement of skin colour that is often visible the moment you apply a moisturiser.
Recently moisturisers have been developed which offer sunless tanning. One of the most effective ingredients for sunless tanning is dihydroxyacetone (DHA). The tan itself is not a dye, stain or paint, but is formed during a chemical reaction between the DHA and amino acids in the uppermost layer of the skin surface - the stratum corneum. This reaction is similar to one well known to food chemists called the Maillard reaction (the browning process which occurs during food manufacturing and storage). It does not involve skin pigmentation nor does it need UV exposure to initiate the color change. The reaction is non-toxic and skin safe, without the damage associated with UV exposure. The tan is temporary and fades slowly over three to ten days.
How many times have you read that skin absorbs 60% of whatever is applied to it? Yet there is no evidence to support this figure. In practise, the skin will absorb anything from 0% to 100% of whatever contacts it but in general the primary function of the skin is to act as a barrier that prevents the intrusion of external materials. Cosmetic companies actually have to work hard to develop formulations that can be absorbed into the skin to deliver all the benefits the consumer expects.
How do self-tanning products work?
See our section on self-tanning products.