How does UV radiation cause skin cancer?

By damaging the skin’s cellular DNA, excessive Ultraviolet (UV) radiation produces genetic mutations that can lead to skin cancer. UV rays react with a substance called melanin that is found within the skin. Melanin plays a role in the first defense system to protect against the sunlight by absorbing the dangerous UV rays which can cause serious damage to our skin. Sunburn occurs when the amount of UV exceeds the level of protection that the skin's melanin can provide. However, a small amount of exposure to sunlight is healthy and pleasurable. Predisposition to skin cancer can be hereditary, meaning that it is passed through the generations of a family through genes.

Basically, there are two different ways by which UV radiations could cause skin cancer:
• By damaging the DNA in skin cells, causing the skin to grow abnormally and develop benign or malignant growths.
• By weakening the immune system and compromising the body’s natural defenses against aggressive cancer cells.

UVA rays have longer wavelengths. They penetrate deeper into the dermis and suppress the immune system to interfere with the ability of immune system to protect against the development and spread of skin cancer. Signs of UVA exposure include premature aging of the skin such as wrinkling and age spots. Long-term exposure can cause damages to the skin's connective tissues, leading to premature aging.

UVA may also aid in the development of skin cancer. According to the research studies done by scientist, UVA does not cause significant damage in areas of the epidermis which is the outermost skin layer where most skin cancers occur, UVA damages the skin cells called keratinocytes in the basal layer of epidermis where most skin cancers occur.

Diagram: A tanning booth. (Amber Desire, 2009)

UVA is used by tanning salon in the tanning booths. UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, can cause cumulative damage over time. The doses of UVA emitted from the high-pressure sunlamps in the tanning booth are as much as 12 times that of the sun. Based on the statistics, people who often visit tanning salons are 2.5 times more likely to develop squamous cell carcinoma, and 1.5 times more likely to develop basal cell carcinoma. According to recent researches, risk of melanoma is 75 percent higher for individuals who had first exposure to tanning beds in youth.

The UVB rays are the sun's burning rays and are the primary cause of sunburn. UVB rays have shorter wavelengths than UVA and are primarily responsible for sunburn and skin cancer. UVB rays can be blocked by window glass. UVB tends to damage the skin’s more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. Its intensity varies by season, location, and time of day. Melanoma, the most dangerous form of skin cancer, is thought to be associated with severe UVB sunburns that occur before the age of 20.