Most skin cancers are a result of exposure to the UV rays in sunlight. Both basal cell and squamous cell cancers (the most common types of skin cancer) tend to be found on sun-exposed parts of the body, and their occurrence is typically related to lifetime sun exposure. The risk of melanoma, a more serious but less common type of skin cancer, is also related to sun exposure, although perhaps not as strongly. Skin cancer has also been linked to exposure to some man-made sources of UV rays.

What do studies show?

Many studies have found that basal and squamous cell skin cancers are linked to certain behaviors that put people in the sun, as well as a number of markers of sun exposure, such as:

• Spending time in the sun for recreation (including going to the beach)

• Spending a lot of time in the sun in a swimsuit

• Living in an area that gets a lot of sunlight

• Having had serious sunburns in the past (with more sunburns linked to a higher risk)

• Having signs of sun damage to the skin, such as liver spots, actinic keratoses (rough skin patches that can be precancerous), and solar elastosis (thickened, dry, wrinkled skin caused by sun exposure) on the neck

Studies have also found links between certain behaviors and markers of sun exposure and melanoma of the skin, including:

• Activities that lead to “intermittent sun exposure,” like sunbathing, water sports, and taking vacations in sunny places

• Previous sunburns

• Signs of sun damage to the skin, such as liver spots, actinic keratoses, and solar elastosis

Because UV rays don’t penetrate deeply into the body, they wouldn’t be expected to cause cancer in internal organs, and most research has not found such links. However, some studies have shown possible links to some other cancers, including Merkel cell carcinoma (a less common type of skin cancer) and melanoma of the eye.

Studies have found that people who use tanning beds (or booths) have a higher risk of skin cancer, including melanoma and squamous and basal cell skin cancers. The risk of melanoma is higher if the person started indoor tanning before age 30  or 35, and the risk of basal and squamous cell skin cancer is higher if indoor tanning started before age 25.

What do expert agencies say?

In general, the American Cancer Society does not determine if something causes cancer (that is, if it is a carcinogen), but we do look to other respected organizations for help with this. Based on the available evidence, several expert agencies have evaluated the cancer-causing nature of UV radiation.

The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). One of its major goals is to identify causes of cancer. Based on the available data, IARC has made the following determinations:

• Solar radiation is carcinogenic to humans.

• Use of UV-emitting tanning devices is carcinogenic to humans.

• UV radiation (including UVA, UVB, and UVC) is carcinogenic to humans.

The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). The NTP has made the following determinations:

• Solar radiation is known to be a human carcinogen.

• Exposure to sunlamps or sunbeds is known to be a human carcinogen.

• Broad-spectrum UV radiation is known to be a human carcinogen.

• UVA radiation is reasonably anticipated to be a human carcinogen.

• UVB radiation is reasonably anticipated to be a human carcinogen.

• UVC radiation is reasonably anticipated to be a human carcinogen.

(For more information on the classification systems used by these agencies, see Determining if Something Is a Carcinogen.)

What about tanning beds?

Some people think that getting UV rays from tanning beds is a safe way to get a tan, but this isn’t true.

Both IARC and NTP classify the use of UV-emitting tanning devices (including sunlamps and tanning beds) as carcinogenic to humans.

The US Food and Drug Administration (FDA), which refers to all UV lamps used for tanning as “sunlamps,” requires them to carry a label that states, “Attention: This sunlamp product should not be used on persons under the age of 18 years.”

The FDA also requires that user instructions and sales materials directed at consumers (including catalogs, specification sheets, descriptive brochures, and webpages) carry the following statements:

• Contraindication: This product is contraindicated for use on persons under the age of 18 years.

• Contraindication: This product must not be used if skin lesions or open wounds are present.

• Warning: This product should not be used on individuals who have had skin cancer or have a family history of skin cancer.

• Warning: Persons repeatedly exposed to UV radiation should be regularly evaluated for skin cancer.

The FDA has also proposed a new rule to ban the use of indoor tanning devices by anyone under age 18, to require tanning facilities to inform adult users about the health risks of indoor tanning, and to require a signed risk acknowledgment from all users.  Some US states have already banned indoor tanning by all people younger than 18, while others have banned use by younger teens and children.

Are there any other health issues related to UV radiation?

In addition to skin cancer, exposure to UV rays can cause other health problems:

• UV rays, either from the sun or from artificial sources like tanning beds, can cause sunburn.

• Exposure to UV rays can cause premature aging of the skin and signs of sun damage such as wrinkles, leathery skin, liver spots, actinic keratosis, and solar elastosis.

• UV rays can also cause eye problems. They can cause the cornea (on the front of the eye) to become inflamed or burned. They can also lead to the formation of cataracts (clouding of the lens of the eye) and pterygium (tissue growth on the surface of the eye), both of which can impair vision.

• Exposure to UV rays can also weaken the immune system, so that the body has a harder time fending off infections. This can lead to problems such as reactivation of herpes triggered by exposure to the sun or other sources of UV rays. It can also cause vaccines to be less effective.

Some people are more sensitive to the damaging effects of UV radiation. Some medications can also make you more sensitive to UV radiation, making you more likely to get sunburned. And certain medical conditions can be made worse by UV radiation.