Sun - the skin’s enemy

  • 4 May 2015
  • Reading time 6 mins
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For many years now we have been aware of the need to stay out of the sun and use sunscreens. Vanity and fashion, however, dictate otherwise. Most of us ‘feel better’ with a a tan - particularly psychologically - and pay good money to spend our annual holiday soaking it up. But what precautions should we take and how does it damage our skin?

The A B C of Ultraviolet

The sun emits many different types of rays. Luckily the stratosphere and ozone filter out shorter rays. If ozone didn’t filter out ultraviolet C, for example, we would not be here, as it destroys DNA. Ultraviolet A and B are of particular concern, although others such as infrared are increasingly being implicated in skin damage too.

UVB rays are shorter than UVA, and they are the ones which cause most damage, although both are harmful. UVB rays penetrate the epidermis and are known as the rays which cause burning. They oxidise the fats in the cell membranes, ruining their barrier function. Some UVB rays manage to get further into the epidermis, causing sunburn which is effectively oxidative damage to the DNA and other proteins. The redness and inflammation caused by sunburn are a result of the oxidation and the dilation of blood vessels as the skin attempts to protect and repair itself. This goes on long after the initial sun exposure and the cascade of oxidants sets the scene for potentially cancerous cell changes later on.

UVA rays cause oxidative damage to cells and the connective tissue in the dermis, which leads to burning and ageing. Initially believed to be less harmful than UVB, it is now known that UVA rays can penetrate further into the skin, into the dermis, where they damage collagen and elastin. With these two important connective tissues destroyed, it is not difficult to see the link between UVA exposure and ageing. UVA rays are, in a way, more insidious because they get through the skin even on a cloudy day and through glass, unlike UVB which can only reach the surface of the earth when the sun is high in the sky.

All the different rays aside, the bottom line is that UV light damages our cells on a molecular level: it interferes with their ability to make proteins and reproduce properly, speeds up the replication of damaged cells, hardens the collagen and elastin which normally keep our skin strong and elastic, breaks down the important fats in the cell membrane and ultimately creates a dry, rapidly ageing skin which is even more susceptible to further damage.

These effects have worsened in recent years because the amount of UV light reaching the earth’s surface is increasing as the protective ozone layer is being depleted. Also, the closer you get to the sun , the more susceptible you are to the effects of UV rays, so i’t even more important to protect yourself from the sun when mountain climbing, skiing or visiting high altitudes.

Natural defences

In the face of this onslaught from the sun, our bodies do have remarkable protective mechanisms. The first defence that comes into play, but only if we carefully control our exposure to the sun, is melanin, the pigment produced in the skin. It absorbs light, and, as exposure continues, more melanin is produced by the melanocytes, creating a suntan. People with darker skin have more melanin, so they are more resistant to the harmful effects of the sun, while albinos have no melanin at all, so they burn severely in even the slightest sun exposure. The keratinocytes also play a protective role by moving the protective pigments - melanin and keratin - towards your skin’s surface to provide your very own sunscreen.

Shiny, wet skin absorbs more light than dry skin because of the way the rays bend through the liquid. This is why putting oil on your skin before sunbathing is likely to increase tanning. Cell membranes in the skin (which are partly composed of oils) are particularly susceptible to damage from UV rays, and it is now accepted that long-term exposure to UV light accelerates the ageing process and the risk of skin cancer.

Unfortunately, melanin is not enough to protect us from the damage caused by the sun. In many people it ‘mutinies’ and dumps melanin in clusters which show up as freckles. The sun causes permanent damage by oxidising the elastin in skin - the proteins become cross-linked and lose their elasticity. The DNA in your cells is also very susceptible to damage. And the havoc caused by damaged DNA is believed to be a major cause of cancer. It also prevents the DNA from sending accurate messages to cells, resulting in changes to the structure of the skin, leaving it less supple, dryer and eventually rather rough and wrinkly. This sort of damage is irreversible.

Another clever defence mechanism the skin employs to protect itself from the sun is altering its thickness. In response to continued attack by UVB (not UVA), the stratum corneum which largely consists of dead, keratin-filled cells, gets thicker. These dead cells offer protection from the sun by absorbing or reflecting a significant amount of UVB.

Our third line of defence is the body’s own antioxidants, sun as vitamins A, C and E, and enzymes which ‘mop up’ some of the oxidant damage caused by the sun. These, however, only have a limited life and are rapidly over-run after just a few minutes in fierce sun. Recent research published by the American Academy of Dermatology showed that sunburn was reduced by taking vitamin C (2000 mg) and vitamin E (1000 iu), both potent antioxidant nutrients.

However, UV light is a very powerful oxidant promoter which can override antioxidant protection. While antioxidant nutrients are extremely effective in protecting us against more general oxidant exposure, the harsh effects of direct sunlight are best avoided altogether.

Super sensitivities

Burning and ageing are just two of the negative effects of the sun. UV rays can also cause harm by suppressing the function of the skin’s immune cells - the Langerhan cells. In some people, they trigger a ......

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