UVB rays are slightly stronger. They are mainly responsible for direct damage to the DNA and are the rays that cause sunburns. They are also thought to cause most skin cancers.

UVC rays are the strongest UV rays. Fortunately, because of their strength, they react with ozone high in our atmosphere and do not reach the ground. Therefore, UVC rays are not present in sunlight and are not normally a risk factor for skin cancer. But they can be found in some manmade sources, such as arc welding torches and mercury lamps. In the past, sunbeds also were a source of UVC rays.

Do UV Rays Cause Cancer? 

Yes. Most skin cancers are direct results of exposure to the UV rays in sunlight. In-transit, basal cell and squamous cell cancers of the body -- the most common types of skin cancer, tend to be found on sun-exposed parts of the body, and they are linked to lifetime sun exposure. Melanoma, a more serious but less common type of skin cancer, is also related to sun exposure.

Cancer Treatments

Some cancer treatments such as chemotherapy and radiation therapy may increase a person's risk of developing a different type of cancer later in life. Advances in radiation therapy, a common cancer treatment, increase the chances of survival for many cancer patients.

Cancer is a common disease, and not all second cancers are due to cancer treatment. For example, certain inherited gene changes can increase a woman's risk for both breast and ovarian cancer. Also, being exposed to certain cancer-causing substances, like tobacco smoke, can put a person at higher risk for several different cancers, such as cancers of the lung, larynx (voice box), throat and mouth.                    

Does Radiation Therapy Cause Cancer?

As these treatments become more common and more successful, studies are being conducted on the long-term effects they have on the patients. Of the possible long-term complications of radiation therapy, developing a second cancer is one of the most serious.