日光与紫外线

来自太阳光的紫外线

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UV radiation

Sunlight and Ultraviolet Radiation

The vast majority of skin cancers are due to unprotected ultraviolet radiation (UV) exposure. Most of this radiation comes from sunlight, but some may come from artificial sources, such as tanning booths. The amount of UV exposure depends on the strength of the light, the length of exposure, and whether the skin is protected.

     大量的皮肤癌是由于在暴露于紫外线时未进行防护。多数紫外线来自日光，但也有一些来自人工的光源。如制革车间。暴露于紫外线的量取决于光照的强度，暴露的时间长短，再就是皮肤是否给予防护。

The short-term results of unprotected exposure to UV rays are sunburn and tanning. Long-term exposure causes prematurely aged skin, wrinkles, loss of elasticity, dark patches (lentigos, that are sometimes called "age spots" or "liver spots"), actinic keratoses. and actual skin cancers. Actinic keratoses are small (usually less than 1/4 inch) rough or scaly spots. Usually they develop on the face, ears, back of the hands, and arms of middle-aged or older people with fair skin, although they can arise on other sun-exposed areas of the skin. Although actinic keratoses are slow-growing and usually do not cause any symptoms, they sometimes turn into squamous cell cancer.

The American Cancer Society estimates more than 1 million new cases of highly curable basal and squamous cell cancers will be diagnosed this year. The most serious form of skin cancer is melanoma, which is diagnosed in about 50,000 people each year and causes several thousand deaths. During the 1970s, the incidence rate of melanoma increased rapidly at about 6% per year. Since 1981, however, the rate of increase slowed to about 3% per year.

Besides skin cancer, the sun's UV radiation also increases the risk of cataracts and certain other eye problems, and can suppress the immune system. And although dark-skinned people are generally less likely to get skin cancer than light-skinned people, they are susceptible to cataracts and immune suppression.

Two main types of UV radiation reach the earth, UVA and UVB. UVB radiation is well known to cause damage to the DNA of skin cells. Skin cancers develop when this damage affects the DNA of genes that control growth and division of skin cells. Recent research has found that UVA also contributes to skin cancer formation. Scientists now believe that both UVA and UVB rays contribute to skin damage, including skin cancer. There are no safe UV rays. 没有！

Everyone's skin and eyes are susceptible to sun damage. Although people with light skin are more susceptible to sun damage, darker skinned people, including African Americans and Hispanic浅色皮肤易受伤害，深色皮肤要好一点（非裔美国人和西班牙人）。

 Americans, also can be affected.

People with darker skin tan more easily than others. Tanning occurs when ultraviolet radiation is absorbed by the skin, causing an increase in the activity and number of melanocytes , the cells that produce the pigment melanin. Melanin helps to block out damaging rays up to a point, which is why darker skinned people burn less easily.

Those with lighter skin are more likely to burn. Too much sun exposure in a short period results in sunburn. A sunburn causes skin redness, tenderness, pain, and in some cases, swelling and blistering as well. Symptoms of a more serious sunburn include fever, chills, upset stomach, and confusion. If these symptoms develop, see a doctor. The long-term consequence of sunburn is more serious than these short-term symptoms, however. UV exposure that is intense enough to cause sunburn will clearly increase a person's risk of developing skin cancer. But, UV exposure can increase skin cancer risk even without causing a sunburn.

Extra care should be taken to protect babies and children from the sun. Studies show that intense exposure, including exposures that lead to sunburns, as a child or teenager could increase the risk for melanoma, sometimes a fatal form of skin cancer.

You need to be especially careful in the sun if you:

要特别在意的人群

• have lots of moles, irregular moles, or large moles （有色素痣）

• were previously treated for skin cancer （曾患皮肤癌）

• work indoors all week and then get a tan on weekends （长期户外工作和每周日光浴的人）

• live or vacation in tropical or subtropical climates （居住在热带和亚热带地区的人或度假的人）

• have freckles and burn before tanning （有雀斑或烧伤的人）

• have fair skin; or blond, red, or light brown hair （白皮肤的人或金发碧眼的人，浅色发的人）

• have a family history of skin cancer, especially melanoma （有家族性皮肤癌特别是黑色素瘤的人）

• live or vacation at high altitudes (ultraviolet radiation from the sun increases 4% to 5% for every 1,000 feet above sea level) （生活在高纬度区的人）

• spend a lot of time outdoors

• have had an organ transplant （进行过器官移植的人）

• have certain diseases, such as lupus erythematosus （红班狼疮）

• take tetracycline, sulfa drugs and some other antibiotics, （服用四环素、磺胺、其他抗生素的人）

• take naproxen sodium and some other nonsteroidal anti-inflammatory drugs, （服用萘普生、非甾体抗炎药的人）

• take phenothiazines (major tranquilizers and anti-nausea drugs) （服用吩噻嗪类药物的人）

• take tricyclic antidepressants （服用三环类抗抑郁药的人）

• take thiazide diuretics (medications used for high blood pressure and some heart conditions) （服用过噻嗪类药物的人）

• take sulfonylureas (a form of oral anti-diabetic medication) （服用过sulfonylureas－－一种抗粮尿病药）

• take medications that reduce immunity （服用抗免疫药物的人）

Ask your doctor, nurse, or pharmacist about the risk of any medicines you may be taking that could be harmful to you if you are exposed to sunlight.

To increase awareness of the damaging potential of UV radiation, the Environmental Protection Agency and the National Weather Service developed the UV Index. The UV index number, ranging from 0 to 10+, indicates the amount of UV radiation reaching the earth's surface during an hour around noon. It is forecast daily for 58 cities, based on locally predicted conditions. The higher the number, the greater the exposure to UV radiation. The UV Index is valid only for about a 30-mile radius from the city, and, as with any forecast, local variability in cloud cover and other factors may change actual levels experienced, but it serves as a reminder to take precautions against UV exposure.

It is impossible to completely avoid sunlight and it would be unwise to reduce your level of activity because you don't want to be outdoors. But there are precautions that you can take to limit your amount of exposure to UV.

Some people think about sun protection only when they spend a full day at the beach or pool. But sun exposure adds up day after day, and it happens whenever you are in the sun, for example when you are gardening, fishing, hiking, riding a bike, going to the zoo, attending a baseball game, or going to and from your car. The following are steps that provide a practical approach to protecting yourself from the effects of the sun.

The intensity of the sun's rays are related to several factors, including closeness to the equator, altitude, season of the year, time of day, cloud cover, and the ozone "hole." Ultraviolet rays are most intense when the sun is high in the sky, during the midday which is usually between the hours of 10 AM and 4 PM. If you are unsure about the sun's intensity, take the shadow test: If your shadow is shorter than you, the sun's rays are the strongest. Plan activities out of the sun during these times. If you must be outdoors, protect your skin.

UV radiation also can pass through water, so don't assume you're safe from UV radiation if you're in the water and feeling cool. Also, be especially careful on the beach and in the snow because sand and snow reflect sunlight and increase the amount of UV radiation you receive.

If you plan to be outdoors, you may want to check the UV Index for your area. The UV Index usually can be found in the local newspaper or on TV and radio news broadcasts. It also may be available through your local phone company and is available on the Internet at the National Weather Service Climate Prediction Center's home page (ww.nnic.noaa.gov/cpc/).

When in the sun, keep your shirt on! Wear clothing to protect as much skin as possible. Long-sleeved shirts, long pants, or long skirts are the most protective. Dark colors provide more protection than light colors by preventing more UV rays from reaching your skin. A tightly woven fabric provides greater protection than loosely woven clothing. If you can see light through a fabric, UV rays can get through, too. Also, dry fabric is generally more protective than wet fabric.

The ideal sun-protective fabrics are lightweight, comfortable, and protect against exposure even when wet. Currently a few companies in the US manufacture sun-protective clothing. The American Society for Testing and Measurement (www.astm.org) has recently developed standards for manufacture and labeling of sun protective products. These will soon be published but have not yet been released.

Swimsuits for children made from sun protective fabric and designed to cover the child from neck to knees are popular in Australia and are available in some areas of the US. Consumers can ask retailers to carry these products.

A hat with at least a 2 to 3-inch brim all around is ideal because it protects areas often exposed to the sun, such as the neck, ears, eyes, forehead, nose, and scalp. A shade cap (which looks like a baseball cap with about 7 inches of material draping down the sides and back) also is good. These are often sold in sports and outdoor clothing and supply stores.

A baseball cap provides some protection for the front and top of the head but not the back of the neck or the ears, where skin cancers commonly develop.

A sunscreen is a product that you apply to the skin for some protection against the sun's ultraviolet rays, although it does not provide total protection. Sunscreens are available as lotions, creams, ointments, gels, and wax sticks.

When selecting a sunscreen product, be sure to read the label before you buy. Sunscreen products labeled "broad-spectrum" protect against UVA and UVB radiation. Some cosmetics, such as some lipsticks, also are considered sunscreen products if they contain sunscreen and their labels state they do.

Experts recommend products with an SPF (Skin Protection Factor) of at least 15. The number of the SPF represents the level of sunburn protection provided by the sunscreen. A SPF 4 blocks out 75% of the burning UV rays while an SPF 15 blocks out 93% of the burning UV rays; an SPF 30 blocks out 97% of the burning UV rays. The FDA is currently reviewing ways to measure how much protection sunscreen products provide in the UVA range.

It is important to remember that sunscreen does not provide total protection. When using an SPF 15 and applying it correctly, you will get the equivalent of 1 minute of burning UV rays each 15 minutes you spend in the sun. So, 8 hours in the sun wearing SPF 15 sunscreen is the same as spending 32 minutes unprotected. Reflective surfaces like water, snow, and sand can actually cause exposure to more UV rays. For high-glare situations, a higher SPF sunscreen or zinc oxide may be used on your nose and lips.

Products labeled "waterproof" provide protection for at least 80 minutes even when swimming or sweating. Products that are "water resistant" may provide protection for only 40 minutes.

Some sunscreen products can irritate some people's skin. Many products claim to be "hypoallergenic" or "dermatologist tested," but the only way to know for sure whether a product will irritate your skin is to apply a small amount to your skin for three days. If your skin does not turn red or become tender and itchy, the product should be okay for you.

Be sure to apply the sunscreen properly. For maximum effectiveness, apply sunscreen 20 to 30 minutes before going outside. Be generous. About one ounce of sunscreen should be used to cover the arms, legs, neck and face of the average adult. Less is needed for a child. For best results, most sunscreens need to be reapplied about every 2 hours.

If swimming or perspiring, don't forget to reapply sunscreen to maintain protection. Remember that sunscreen usually rubs off when you towel yourself dry.

Use sunscreen lip balm.

If you or your child burn easily, be extra careful to cover up, limit exposure, and apply sunscreen. Also, be sure to use sunscreen if you or your child are taking medications that can make the skin more sensitive to the sun.

Use hats, clothing, and shading to protect babies younger than 6 months from the sun. If shade or protective clothing is not available, very small amounts of sunscreen can be used on small areas, such as the face and the back of the hands.

For children 6 months to 2 years, use a sunscreen with at least an SPF 15.

Research has shown that long hours in the sun without adequate eye protection increase the chances of developing eye disease. UV-absorbent sunglasses can help protect your eyes from sun damage.

The ideal sunglasses do not have to be expensive, but they should block 99% to 100% of UVA and UVB radiation. Check the label to be sure they do. Some labels may say, "UV absorption up to 400 nm" which is the same as 100% UV absorption. Also, labels that say "special purpose" or "Meets ANSI UV Requirements" mean the glasses block at least 99% of UV rays. Those labeled "cosmetic" block about 70% of the UV rays. It there is no label, don't buy the sunglasses. (The American National Standards Institute ANSI sets standards for sunglasses' UVA/UVB protection. They require that sunglasses block a minimum of 50% of UV.)

Darker glasses are not necessarily better because the UV protection comes from an invisible chemical applied to the lenses, not from the color or darkness of the lenses. Look for an ANSI label.

Ideally, all types of eyewear, including prescription glasses, contact lenses, and intraocular lens implants used in cataract surgery, should absorb the entire UV spectrum. Large-framed wraparound sunglasses protect your eyes from all angles. Children need smaller versions of real, protective adult sunglasses-- not toy sunglasses.

Many people believe that the UV rays of tanning beds are harmless. This is not true. Tanning lamps emit UVA and frequently emit a lot of UVB also. Both UVA and UVB can cause serious skin damage, and both contribute to formation of skin cancers. Because of these dangers, health experts advise people to avoid sunlamps for tanning.

Sunlamp products are regulated by the US Food and Drug Administration (FDA). According to their regulations, sunlamp products must:

• have a timer to limit the amount of exposure a person can receive in one session.

• have a label with recommended exposure position or distance from the sunlamp to reduce the risk of overexposure, even when the timer is set at its maximum limit.

• limit the amount of short-wave UV radiation emitted from the product. come with UV-blocking goggles, which the user should always wear.

• carry a prominent warning about the dangers of overexposure, especially to those who are sensitive to UV radiation.

• provide information on proper use.

You can improve your chances of finding precancerous skin conditions, such as actinic keratosis -- (a dry, scaly, reddish, and slightly raised lesion) and skin cancer by examining your skin regularly. The earlier you identify signs and see your health care provider, the greater the chances for simple and successful treatment.

The best time to examine your skin is after a shower or bath. Check yourself in a well-lighted room using both a full-length mirror, and a hand-held mirror. Become familiar with your birthmarks, moles and blemishes so that you know what they usually look like and then can easily identify any changes they undergo. Signs to look for are changes in size, texture, shape, and color of blemishes or a sore that does not heal. If you find any changes, see your doctor or health care provider. Also, during regular checkups, ask your doctor to check your skin.

Several products that claim to give a tan without UV radiation carry safety risks, too. These include so-called "tanning pills" containing carotenoid color additives derived from substances similar to beta-carotene, the substance that gives carrots their orange color. The additives are distributed throughout the body, especially the skin, making it orange. Although the FDA has approved some of these additives for coloring food, it has not approved them for use in tanning agents. And, at the high levels that are consumed in tanning pills, they may be harmful. The main ingredient in sunless tanning pills, canthaxanthin, can deposit in the eyes as crystals, which may cause injury and impaired vision. There also has been one reported case of a woman who died from aplastic anemia, which her doctor attributed to her use of tanning pills.

Tanning accelerators, such as those formulated with the amino acid tyrosine or tyrosine derivatives, are ineffective and also may be dangerous. Marketers promote these products as substances that stimulate the body's own tanning process, although evidence suggests they don't work. FDA considers them unapproved new drugs that have not been proven safe and effective.

Two other sunless tanning products, bronzers and extenders, are considered cosmetics for external use and are not harmful. Bronzers, made from color additives approved by FDA for cosmetic use, stain the skin when applied and can be washed off with soap and water. Extenders, when applied to the skin, interact with protein on the surface of the skin to produce color. The color tends to wear off after a few days. The only color additive approved for extenders is dihydroxyacetone.

Although they give skin a golden color, these products do not offer protection from the damaging effects of UV radiation. Also, the chemicals in bronzers may react differently on various areas of your body, producing a tan of many shades.

• Examine your body front and back in the mirror, then your right and left sides with arms raised.

• Bend elbows and look carefully at forearms and upper underarms and palms.

• Look at back of your legs, your feet, your soles, and the spaces between your toes.

• Examine the back of your neck and scalp with the help of a hand mirror, and part hair to lift it to give yourself a closer look.

The most common skin cancers-basal cell and squamous cell-often take the form of a pale, wax-like, pearly nodule, a red scaly, sharply outlined patch, or a sore that does not heal. Another form of skin cancer - melanoma - often starts as a small, mole-like growth.

The ABCD rule is a convenient guide to the usual signs of melanoma. Be on the look out and notify your physician about any changes in the following factors:

• A is for ASYMMETRY: One-half of a mole or birthmark does not match the other.

• B is for BORDER: The edges are irregular, ragged, notched, or blurred.

• C is for COLOR: The color is not the same all over, but may have differing shades of brown or black, sometimes with patches of red, white, or blue.

• D is for DIAMETER: The area is larger than 6 millimeters (about ?inch -- the size of a pencil eraser) or is growing larger.

Other important warning signs of melanoma include changes in size, shape, or color of a mole or the appearance of a new spot. Some melanomas do not fit the ABCD rule described above, so it is particularly important for you to be aware of changes in skin lesions or new skin lesions.

Are you prepared for a safe summer in the sun? Take our test and find out!

FALSE: Sunscreens are useful in reducing the risk of skin cancer, but they don't provide total protection from ultraviolet rays. The best way to protect yourself is to seek shade and limit your time in the sun during the midday hours when the sun is at its strongest. Cover up with a shirt and hat, use a sunscreen with an SPF rating of 15 or higher, and remember sunglasses for eye protection.

FALSE: Sun exposure can increase your risk of skin cancer, but it's not the only cause. People who spend a lot of time in the sun are at highest risk for the most common types of skin cancers (known as non-melanoma cancers). Occasional exposure (such as on the weekends) to strong sunlight seems to increase the risk for melanoma, a less common, but more serious skin cancer. If you have a family history of melanoma, you may be genetically predisposed and should take extra precautions.

TRUE: But remember to read the label! "Waterproof" sunscreens may only last for an hour and 20 minutes of swimming and/or sweating. If indicated on the label, some sunscreens may protect you for longer periods of time, but be sure to reapply as necessary.

FALSE: The temperature doesn't matter-the ultraviolet rays do. Ultraviolet rays are most intense when the sun is high in the sky. Take the shadow test -- if your shadow is shorter than you, the sun's rays are the strongest. Ultraviolet rays can penetrate clouds, so it's important to take precautions even on hazy days and days with light cloud cover.

FALSE: Outdoor activity helps maintain your physical and emotional well being. Just remember to seek the shade, and wear sunscreen, appropriate clothing, and sunglasses.

For more information, please see our information on Melanoma Skin Cancer and Nonmelanoma Skin Cancer

American Academy of Dermatology. Patient Information. Available online at: www.aad.org

American Academy of Pediatrics. Summer Safety Tips. Available online at: www.aap.org/advocacy/archives/summertips.htm.

FDA. Center for Devices & Radiological Health. The Darker Side of Tanning. February 4, 1997.
　

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