Ultraviolet Rays
The sun emits many different types of rays. Luckily the 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 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, in effect, 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 to 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, harms 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, due to chemical reactions between it and various chemicals found in refrigerators and some spray cans. Also, the closer you get to the sun, the more susceptible you are to the effects of UV rays, so it's even more important to protect yourself from the sun when mountain climbing, skiing or visiting high altitudes.
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