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Summer 1999

Good Day, Sunshine: Staying Safe in the Sun

     by Geoffrey Skinner

     Many of us escape to the outdoors whenever possible, especially in the summer, when the weather invites hikes, rides, and backpacking trips to the mountains, along with visiting the beaches, swimming, etc. As a child, I spent hours under the California sun with few clothes on, let alone sun block, and was tanned a dark brown every summer. These days, however, very few of us are likely to spend long outside without some sort of sun protection. News about the thinning ozone layer and general warnings about skin damage from the sun's rays abound. The "healthy" tan no longer has appeal it once did; even Doonesbury's Zonker long ago left the world of tanning competitions. With that in mind, I don't wish to simply admonish against going out in the sun, but explore the options and the science of sun protection.

Why UV radiation is a concern

     Ultraviolet radiation from the sun comes in three flavors: UVA, UVB and UVC, all of which are harmful to unprotected skin. UVA has a wavelength just slightly shorter than visible violet light (320-400 nanometers) and is not blocked by the ozone layer. UVA has the potential to penetrate the most deeply into the skin. UVB is the next shorter wavelength (280-320 nm) and is partially blocked by the ozone layer. UVB is the most dangerous for humans (and other organisms) and can cause DNA damage and skin cancers. UVC has the shortest wavelength (shorter than 280 nm) and is also harmful, but fortunately, UVC is completely absorbed by the ozone layer and ordinary oxygen. Altogether, the ozone layer and stratospheric oxygen absorb 97-99% of UV radiation shorter than 300 nm.
      Especially for light-skinned people, reducing and preventing exposure to UVB radiation is important for long-term health, particularly as the ozone layer continues to thin. A small increase in the amount of UVB radiation will cause a large increase in the number of basal and squamous-cell carcinomas; some researchers estimate that 90% of skin carcinomas are attributable to UVB exposure. Fortunately, most are easily treatable and rarely fatal if detected early. Melanoma growth appears to be correlated to brief, high-intensity exposure (as long as 10-20 yr. before its appearance!) and the link is indisputable between UV exposure of all varieties and premature aging of the skin. Even mild tanning alters the skin DNA and damages the connective tissues. There is no such thing as a safe tan!
      In addition to skin damage, UV light can damage the eyes, particularly the cornea, which is a good UV absorber. High doses can cause temporary clouding of the corneas, which is the cause of "snow-blindness." Even more insidiously, ultraviolet radiation can suppress the immune system, which plays a part in skin cancer growth, but may also be a factor in the body's ability to fight off other diseases.
      How much UVB you absorb depends on several factors, including latitude and elevation, cloud cover and proximity to an industrial area. The higher the elevation, the thinner the atmosphere above you, and so the more UVB will strike you. The closer you are to the equator (or to the summer solstice), the more direct the sun's rays, likewise increasing exposure. Cloudy skies will absorb a significant portion of UVB - as much as 50% or more on rainy or substantially overcast days (partially or variably cloudy days do little to reduce exposure). Photochemical smog containing ozone also reduces the amount of UV radiation, which may help explain why the great ozone losses over the southern hemisphere have not been mirrored in the northern one.

Reducing exposure

     If we didn't all enjoy the outdoors, staying out of the sun might seem a reasonable solution, but for many of us, including me, an all-day jaunt in the mountains or a trip to the beach are pleasures which we would be loath to forgo entirely. Fortunately, a number of simple steps are available to allow us to continue our days outdoors in relative safety.

Wear sun-protective clothing. Any clothing will help protect against the sun, but the tighter the weave, the better. One rule of thumb is to check the amount of light that you can see through the fabric. Some clothing is marketed as incorporating special sun-protective fabric with an SPF (Sun Protection Factor) of 30 or more. In general, minimize the amount of bare skin as much as possible. A loose fit also helps by preventing rays from passing directly through the fabric and into your skin.

Wear a hat. The neck, ears and face and eyes are particularly vulnerable to sun damage. Wide brimmed hats (3" or more) offer the greatest protection. Baseball caps may be comfortable, but don't shade very much of the head. In Australia, where the periodic hole in the ozone layer allows large amounts of UV radiation to hit the earth, wide brimmed hats (and sunglasses) are mandatory parts of school uniforms.

Wear sunglasses. Make sure that your sunglasses will block UV rays. Look for peel-off labels stating the amount of blockage; although any glasses (including ordinary glasses) will block some UV, a rating of 100 is best. Sunglasses lacking a label won't necessarily block a significant portion.

Use sunscreen on unprotected skin. A sunscreen with an SPF at least 15 will block most UV, although it must be applied liberally and reapplied every two hours if you are working, exercising or playing outdoors. Even waterproof sunscreen can be wiped off by toweling after swimming. The effectiveness of sunscreen greatly depends on your skin type.

Avoid unnecessary exposure to UV radiation. Stay away from tanning parlors and sun lamps. There is no safe tanning. Pay attention to the UV Index if it is available in newspapers or on TV. This index developed by the Environmental Protection Agency rates UV radiation from 1-15, with anything 10 or higher considered as extremely high. Also consider cloud cover and time of year if the UV Index is not available.

Finally, stay out of the sun at peak hours. UV radiation is most intense in the six hours closest to noon (or 1 p.m. during daylight saving time). The amount of radiation at 10 a.m. and 4 p.m. is half that of 1 p.m. DST. Schedule your outings for mornings or evenings - in addition to reducing sun damage, you may be rewarded by lower temperatures and more wildlife sightings. Siestas have a lot going for them.

     For more information about protecting yourself from sun while still enjoying the outdoors, you may wish to call or write some of the following federal agencies which have information on the effects of UV exposure, UV protection and related issues. Public inquiry telephone numbers are provided where available.

NOAA/National Weather Service National Meteorological Center
Washington, DC 20233
(for information on Experimental UV Index)

National Institute for Occupational Safety and Health (NIOSH)
Technical Information

EPA Stratospheric Ozone Information Hotline

Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
Division of Cancer Prevention and Control
4770 Buford Highway NE,
Mailstop K-57
Atlanta, GA

Be Sun Wise! Program
401 M Street SW (6205J)
Washington DC 20460

Cancer Information Service
National Cancer Institute

     Your physician, dermatologist or local hospital/clinic should also be able to provide you with more detailed information on sun protection and preventing skin cancer.


The Experimental Ultraviolet Index factsheet. EPA/NOAA, 1994.

Action steps for sun protection. EPA, 1995.

Sperling, Brien. Ultraviolet radiation. NASA, 1999.

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