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.
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 is the pigment that gives the skin, hair and iris of the eyes their colour. Individuals with darker skin, have higher amounts of 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...