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Skin Cancer & UV


In this section you can learn about skin cancer and its primary cause, UV radiation. Find answers to common questions by clicking on the links below:

About Skin Cancer

About UV Rays

About Skin Cancer

How common is skin cancer?
This year more than three million Americans will be diagnosed with skin cancer. That's more than all other types of cancer combined. Over 10,000 Americans (more than one per hour) will die from the disease.

The incidence of malignant melanoma in the U. S. has been increasing faster than any other type of cancer and has doubled since 1973. The annual incidence rate of melanoma in California is higher than the national average. This year in California, it is estimated that there will be 5,810 new cases of melanoma and 845 deaths from the disease.1

1California Cancer Registry, California Department of Health Services

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How common is melanoma in California?

California Melanomas of the Skin

Source: NCI SEER Stats,

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Are there different types of skin cancer?
Yes, the three most common types of skin cancer are:

Each of these cancers is named for the type of skin cell from which it arises. Melanoma is a malignancy of the skin’s pigment-producing cells or melanocytes. Squamous cell carcinoma is a malignancy of the cells of the middle or upper epidermis, while basal cell carcinoma occurs when the cells at the base of the epidermis turn malignant.

Melanoma is less common than the other two types of skin cancer, but is far more deadly. It is almost always curable in its early stages, but because of its potential to metastasize (spread to other regions of the body), early detection and treatment are crucial.

Squamous cell carcinoma is not as aggressive as melanoma. Cure rates are in excess of 95% when the tumor is detected and treated early. Chronic overexposure to the sun, as might occur with outdoor employment is a major cause. Actinic keratosis (AK) is a very common skin lesion which is now recognized as the earliest stage in the development of skin cancer. Left untreated, these lesions can progress to squamous cell carcinoma.

Basal cell carcinoma is the most common and least aggressive type of skin cancer. However, it can be quite destructive and has the potential to spread if left untreated.

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What does skin cancer look like?
Melanoma most commonly has the appearance of an unusual mole. It frequently exhibits the “ABCD’s” of: Asymmetry, Border irregularity, Coloration which is dark or in multiple shades, and Diameter the size of a pencil eraser of larger. Melanoma can appear on previously normal skin, or can develop in a pre-existing mole. A pigmented skin lesion that is new, enlarges, changes shape, darkens or looks odd compared to typical moles, is cause for concern.

Squamous cell carcinoma usually appears as a reddish-colored firm lump or plaque with a scaly surface. Actinic keratosis (a precursor of squamous cell carcinoma) is a small pinkish scaly patch. Each of these irregularities is most commonly found on areas of the body that have been chronically exposed to the sun, such as the face, ears, hands, and the scalp of bald men.

Basal cell carcinoma, in its classic form, is a small bump with a translucent quality. It is somewhat red due to enlarged “bloodshot” vessels on its surface. As it grows larger, the surface often ulcerates or forms a scab.

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Who is at risk?
Your risk of UV damage and skin cancer depends on:

Skin's susceptibility to burning can be determined on a six-point scale as shown in the following table1:

Skin Type Tanning and Sunburning History
I Always burns, never tans, sensitive to sun exposure
II Burns easily, tans minimally
III Burns moderately, tans gradually to light brown
IV Burns minimally, always tans well to moderately brown
V Rarely burns, tans profusely to dark
VI Never burns, deeply pigmented, least sensitive

Though everyone is susceptible to damage as a result of excessive sun exposure, people with skin types I and II are at highest risk.

1 Fitzpatrick TB. Arch Dermatol. Jun 1988:124(6):869-71.

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What does skin cancer cost to treat?
While most skin cancer is curable with minor surgery, the sheer number of cases makes this a very costly disease. The 2004 tab for treating skin cancer and Actinic Keratosis in the U.S. was $2.9 billion according to the Society of Investigative Dermatology and the American Academy of Dermatology. This does not include the indirect costs of lost productivity or decreased quality of life. Sun protection would not only help to prevent human suffering, but would significantly reduce health care costs as well.

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Can skin cancer be prevented?
Yes! Skin cancer is largely preventable by avoiding overexposure to UV radiation. Most people attain up to 25% of their lifetime sun exposure before their 18th birthday1 and just two or more blistering sunburns during adolescence nearly doubles the risk of melanoma.2 Make sure to:

1Godar, DE: UV doses of young adults. Photochem and Photobiol. 2003;77(4):453-457
2Weinstock MA, Colditz GA, Willett WC, et al. Pediatrics. Aug1989;84(2):199-204

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About UV Rays

What are ultraviolet (UV) rays? UV rays are invisible waves of radiation generated by the sun. While some of the sun’s radiation is in the form of visible light and heat, UV rays are shorter in length. This shorter wavelength gives UV its capacity to penetrate into the skin. The one beneficial result is the conversion of vitamin D into its active form. However, UV rays are also just the right length to damage cells and to act as a human carcinogen.

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Are there different kinds of UV rays?
Yes. Ultraviolet radiation is actually a continuous spectrum of wavelengths which scientists have divided into three categories, UVA, UVB, and UVC. Rays with the longest wavelength are designated as UVA. UVB rays are shorter, and UVC rays are the shortest of all. Because ozone in the atmosphere absorbs all UVC and most UVB, 95 percent of the radiation reaching the surface of the earth is UVA while just 5% is UVB. UVB penetrates only into the epidermis (upper layer) of the skin but is the major cause of sunburns. UVA penetrates more deeply, down into the dermis of the skin. Tanning beds emit mostly UVA, however both UVA and UVB are highly damaging and can cause skin cancer.

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How do UV rays damage the skin?
When ultraviolet radiation strikes the skin, the rays penetrate beneath the surface and can damage an epidermal cell’s genetic material, or DNA. While the body can usually repair the damage, sometimes this mechanism fails, resulting in a mutation. The skin cancer that can result is named for the type of cell where the mutation occurred. For example, melanoma is a tumor of malignant melanocytes.

UV rays can also damage the dermis and suppress the skin’s immune system, both of which contribute to cancer formation in the epidermis above. Solar damage to the dermal collagen and elastic fibers is a major contributor to skin aging, manifested as wrinkling and sagging.

An illustration of how UV rays damage the skin

When UVB rays penetrate into the skin, they are just the right wavelength to be absorbed by the cell’s genetic material, or DNA. Such bombardment of the DNA can cause it to break apart. While the body can repair most of these molecular injuries, sometimes this mechanism fails, especially in the case of a large dose of radiation, such as a sunburn. This results in mutations which can lead to cancer.

UVA rays penetrate more deeply. They contribute to the formation of skin cancer by inhibiting the tumor suppressive action of the body’s immune cells in the dermis.

In addition to causing skin cancer, damage done by UV exposure includes:

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Are tanning beds safe?
No. UVA is the predominant wavelength provided by most tanning beds. Don’t be fooled just because UVA is less likely to cause sunburn than UVB. The ultraviolet radiation emitted by tanning lights is declared to be a known human carcinogen by the U.S. Government. There is no safe dose of a carcinogen. The U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC), as well as the American Academy of Dermatology (AAD), encourage people to avoid using tanning beds or sun lamps.

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What determines UV intensity?

Time of Year
Time of Year: The sun's angle varies with the seasons, causing the intensity of UV rays to change. UV intensity tends to be highest during the summer months.

Time of Day
Time of Day: The amount of UV varies throughout the day. The period of highest danger is between 10 a.m. and 4 p.m.

Scattered & Reflected Rays
Scattered and Reflected UV Rays: UV rays reflect off snow, water, sand, and concrete. Thin cloud cover scatters UV rays in all directions and allows UV rays to reach your skin even when you are wearing a hat or are under an umbrella.

Altitude: UV rays are more intense at higher altitudes because the thinner atmosphere filters out fewer UV rays. UV rays increase approximately 4% with every 1,000 feet above sea level.

Latitude: UV rays are strongest close to the equator because the sun is more directly overhead. UV rays must travel through less ozone before hitting the earth in these areas. The ozone layer is also naturally thinner in the tropics. At higher latitudes, the UV rays enter the ozone layer at an angle, which decreases UV intensity.

Climate/weather: Clouds block some UV rays from hitting the earth and decrease the UV intensity. However, clouds do not block all UV rays and it is possible to sunburn on cloudy days.

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What is the UV Index?
The UV Index was developed by the National Weather Service and the Environmental Protection Agency. It provides a forecast of the expected risk of overexposure to UV rays and indicates the degree of caution you should take when outdoors. It predicts exposure levels on a 0 to 11+ scale, where values of 2 or less indicate a low danger, while 11+ signifies an extreme risk of harm from unprotected sun exposure. Get in the habit of checking the UV index. It is available online and printed on the weather page of many newspapers.

UV Index Expected Risk and Precautions
2 or less:

A UV Index reading of 2 or less means low danger from the sun's UV rays for the average person:

  • Wear sunglasses on bright days. In winter, reflection off snow can nearly double UV strength.
  • If you burn easily, cover up and use sunscreen.

A UV Index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure.

  • Take precautions, such as covering up, if you will be outside.
  • Stay in shade near midday when the sun is strongest.

A UV Index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Apply a sunscreen with a SPF of at least 15. Wear a wide-brim hat and sunglasses to protect your eyes.

  • Protection against sunburn is needed.
  • Reduce time in the sun between 10 a.m. and 4 p.m.
  • Cover up, wear a hat and sunglasses, and use sunscreen.
Very High

A UV Index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Minimize sun exposure during midday hours, from 10 a.m. to 4 p.m. Protect yourself by liberally applying a sunscreen with an SPF of at least 15. Wear protective clothing and sunglasses to protect the eyes.

  • Take extra precautions. Unprotected skin will be damaged and can burn quickly.
  • Minimize sun exposure between 10 a.m. and 4 p.m. Otherwise, seek shade, cover up, wear a hat and sunglasses, and use sunscreen.

A UV Index reading of 11 or higher means extreme risk of harm from unprotected sun exposure. Try to avoid sun exposure during midday hours, from 10 a.m. to 4 p.m. Apply sunscreen with an SPF of at least 15 liberally every 2 hours.

  • Take all precautions. Unprotected skin can burn in minutes. Beachgoers should know that white sand and other bright surfaces reflect UV and will increase UV exposure.
  • Try to avoid sun exposure between 10 a.m. and 4 p.m.
  • Seek shade, cover up, wear a hat and sunglasses, and use sunscreen.

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What’s the UV Index for my city?
Find the UV Index in your neighborhood by entering your zip code below.

Zip Code:

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How can overexposure to UV rays be avoided?
We cannot stay completely out of the sun. There will be many occasions when we need or desire to be outdoors for exercise, work, or recreation. However, by taking relatively simple steps, most sun damage can be avoided.

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Promoting Sun Safety in California Elementary Schools.

Sun Safe Schools Home Page