大象tv

UV (ultraviolet) radiation is a type of electromagnetic radiation. Like all radiation, UV radiation is energy that spreads as it travels. Exposure to UV, either from the sun or other sources, is a major risk factor for skin cancer.

Types of UV radiation

Different types of radiation are described by the amount of energy particles (photons) they have and give off.

There are different types of UV rays, based on how much energy they have. They are all a type of electromagnetic radiation, which is energy that travels in waves at the speed of light. UV is close to the middle of the electromagnetic spectrum, just above visible light.

Types of electromagnetic radiation that are lower in energy (lower frequency) include microwaves and radio waves. Higher energy (higher frequency) radiation includes x-rays and gamma rays.

Higher energy types of radiation are called ionizing radiation. This means they have enough energy to remove an electron from (ionize) an atom or molecule. Ionizing radiation can damage the DNA (genes) in cells, which in turn may lead to cancer.

Some higher types of UV radiation are ionizing, but even the highest-energy UV rays don’t have enough energy to penetrate deeply into the body, so their main effect is on the skin.

UV radiation is divided into 3 main groups:

• UVA rays have the least energy of UV rays. These rays can cause skin cells to age and can cause some indirect damage to cells’ DNA. UVA rays are mainly linked to long-term skin damage such as wrinkles, but they are also thought to play a role in some skin cancers.
• UVB rays have slightly more energy than UVA rays. They can damage the DNA in skin cells directly and are the main rays that cause sunburns. They are also thought to cause most skin cancers.
• UVC rays have more energy than the other types of UV rays. Fortunately, they don’t reach the ground because they react with ozone high in our atmosphere. So, they are not normally a risk factor for skin cancer. But UVC rays can also come from some man-made sources, such as arc welding torches, mercury lamps, and UV sanitizing bulbs used to kill bacteria and other germs (such as in water, air, food, or on surfaces).

How are people exposed to UV radiation?

Sunlight

Sunlight is the main source of UV radiation and both UVA and UVB rays can damage your skin. This is because the different types of UV rays reach the ground in different amounts. About 95% of the UV rays from the sun that reach the ground are UVA rays, with the remaining 5% being UVB rays.

The amount of UV exposure a person gets depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen. To learn more, see What Factors Affect UV Risk?

Artificial sources of UV rays

People can also be exposed to artificial sources of UV rays. These include:

• Sunlamps and sunbeds (tanning beds and booths): The amount and type of UV radiation someone is exposed to from a tanning bed (or booth) depends on the specific lamps used in the bed, how long a person stays in the device, and how many times the person uses it. Most UV tanning beds emit mostly UVA rays, with the rest being UVB.
• Phototherapy (UV therapy): Some skin problems (such as psoriasis) are helped by treatment with UV light. One type of treatment, called PUVA, uses UVA radiation along with a drug called psoralen that makes the skin more sensitive to UV. Another treatment option uses UVB alone, without a drug.
• Black-light lamps: These lamps use bulbs that give off UV rays (mostly UVA). The bulb also gives off some visible light, but it has a filter that blocks most of that out while letting the UV rays through. These bulbs have a purple glow and are used to view fluorescent material. Bug-zapping insect traps also use “black light” that gives off some UV rays, but the bulbs use a different filter that causes them to glow blue.
• Mercury-vapor lamps: Mercury-vapor lamps can be used to light large public areas such as streets, stadiums, or gyms. They do not expose people to UV rays if they are working properly. They are actually made up of 2 bulbs: an inner bulb that emits light and UV rays, and an outer bulb that filters out the UV. UV exposure can only occur if the outer bulb is broken. Some mercury-vapor lamps are designed to turn themselves off when the outer bulb breaks.
• High-pressure xenon and xenon-mercury arc lamps, plasma torches, and welding arcs: Xenon and xenon-mercury arc lamps are used as sources of light and UV rays for many things, such as UV “curing” (of inks, coatings, etc.), disinfection, to simulate sunlight (to test solar panels, for example), and even in some car headlights. Most of these, along with plasma torches and welding arcs, are mainly of concern in terms of workplace UV exposure.

Does UV radiation cause cancer?

Exposure to UV rays, whether from sunlight or tanning devices, is a risk factor for all types of skin cancer. The risk is higher for people with a weakened immune system, a personal or family history of skin cancer, and if they have large or many moles on their skin.

Most skin cancers are a result of exposure to the UV rays in natural sunlight.

• Basal cell and squamous cell cancers are the most common types of skin cancer and tend to form on sun-exposed parts of the body. They are typically related to lifetime sun exposure.
•  Melanoma is a more serious but less common type of skin cancer. It is also related to sun exposure.

Skin cancer has also been linked to exposure to some artificial sources of UV rays, including tanning devices.

What do studies show about exposure to natural (solar) UV rays in sunlight

Many studies have found that basal and squamous cell skin cancers are linked to certain behaviors as well as a history of having sunburns and sun-related skin damage, such as:

• Spending time in the sun for recreation (including going to the beach)
• Spending a lot of time in the sun with unprotected or exposed skin
• 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 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 have not been found to cause cancer in internal organs. However, some studies have shown possible links between UV rays and some other cancers, including Merkel cell carcinoma (a less common type of skin cancer) and melanoma of the eye.

What do studies show about exposure to artificial UV rays in tanning devices?

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.

• Indoor tanning can increase the risk of basal cell skin cancer by 24% and squamous cell skin cancer by 58%.

The risk of melanoma is about 60% higher if a person starts indoor tanning before age 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 about exposure to UV radiation?

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 (carcinogenic) 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.

The US Food and Drug Administration (FDA), which refers to all UV lamps used for tanning as “sunlamps,” requires them to carry labels that:

• Clearly inform people about the risks of using tanning beds
• Advise frequent users of tanning devices to be regularly checked for skin cancer
• State tanning lamps are not recommended for people under 18 years old

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

The American Academy of Dermatology Association (AADA) has a position statement about indoor tanning that states the AADA:

• Opposes the overall use of indoor tanning devices
• Recommends that people under 18 (minors) do not use indoor tanning devices
• Supports restrictions being put on indoor tanning
• Does not support any statements that promote indoor tanning as “safe”

Are there any other health issues related to UV radiation?

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

• Sunburn due to damage from UV rays from the sun and indoor tanning devices
• Skin damage that leads to premature aging of the skin and signs of sun damage such as wrinkles, leathery skin, liver spots, actinic keratosis, and solar elastosis.
• Eye problems due to UV rays causing the cornea (on the front of the eye) 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.
• Weakened immune system causing the body to have 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.
• Certain 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.