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What Is Skin Cancer?

Normal human skin showing the outermost epidermis, the dermis, and the hypodermis.

Normal human skin showing the outermost epidermis, the dermis, and the hypodermis.

Skin cancer is the most common form of cancer in the United States. The two most common types of skin cancer—basal cell and squamous cell carcinomas—are highly curable, but can be disfiguring and costly. Melanoma, the third most common skin cancer, is more dangerous and causes the most deaths. The majority of these three types of skin cancer are caused by exposure to ultraviolet (UV) light.

Ultraviolet (UV) Light

Ultraviolet (UV) rays are an invisible kind of radiation that comes from the sun, tanning beds, and sunlamps. UV rays can penetrate and change skin cells.

The three types of UV rays are ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC)—

  • UVA is the most common kind of sunlight at the earth’s surface, and reaches beyond the top layer of human skin. Scientists believe that UVA rays can damage connective tissue and increase a person’s risk of skin cancer.
  • Most UVB rays are absorbed by the ozone layer, so they are less common at the earth’s surface than UVA rays. UVB rays, which help produce vitamin D in the skin, don’t reach as far into the skin as UVA rays, but they still can be damaging.
  • UVC rays are very dangerous, but they are absorbed by the ozone layer and do not reach the ground.

In addition to sunburn, too much exposure to UV rays can change skin texture, cause the skin to age prematurely, and can lead to skin cancer. UV rays also have been linked to eye conditions such as cataracts.

The National Weather Service and the Environmental Protection Agency developed the UV Index to forecast the risk of overexposure to UV rays. It lets you know how much caution you should take when working, playing, or exercising outdoors.

The UV Index predicts exposure levels on a 1–15 scale; higher levels indicate a higher risk of overexposure. Calculated on a next-day basis for dozens of cities across the United States, the UV Index takes into account clouds and other local conditions that affect the amount of UV rays reaching the ground.

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