ULTRA VIOLET RAYS
The Ultra Violet rays consist of UVA, B and C.

The UVC rays are the shortest of the Ultra Violet rays. These are potentially the most harmful but are totally screened out by the upper ozone layer. However, as this ozone layer is damaged, the danger grows.

UVB rays cause the most immediate damage to skin in the form of sunburn. These rays penetrate the epidermis and activate the melanocyte cells that produce melanin which, in turn, results in a darker complexion or tan. UVB's are the primary cause of skin cancer, especially in combination with UVA. Further, UVB rays depress the immune system. (Notice how tired and drained you feel after a significant time in the sun. That's the depressant effect). UVB's are only moderately screened by clouds but are reduced significantly by any natural block such as glass or clothing. They are less pervasive than UVA, and they are affected by both factors: time of year, closeness to the sun (they're 20% stronger for each 5,000 feet of elevation). UVB's are also easily reflected, so you get 17% more UVB concentration from sand and 40% more off water.

UVA rays are the third group of light rays and the main cause of premature aging of the skin. They cause wrinkles, age spots, and loss of elasticity. Unlike the other two, these rays easily penetrate the ozone layer. They also penetrate through the top layer (epidermis) of the skin and deeply into the dermis. Together with UVB'S, they cause real damage, killing skin cells, dilating blood vessels to produce a reddish skin or sunburn and destroying the vitamins in the skin causing the connective tissue to be destroyed.

The UVA rays also stimulate melanin but more slowly and safely. Unlike UVB, they are more pervasive and penetrate glass and other barriers. Thus, on a long sunny drive, the side of the body nearest the car window will feel the heat and also develop some color. UVA rays are 10 to 100 times more numerous than UVB