The sun releases many kinds of radiation, but the type of radiation which is most significant to health on earth is ultraviolet radiation. There are two main types of ultraviolet radiation which reach the earth: ultraviolet B (UVB) and ultraviolet A (UVA). Both UVB and UVA have significant effects on human skin. The most important effect of ultraviolet radiation is that it damages the chromosomes in the cells of the epidermis, eventually leading to unattractive brown spots, rough precancerous lesions, and, ultimately, skin cancer if the exposure is high enough. It should be stressed that these effects are cumulative, i.e., every time you are exposed to ultraviolet light you get further damage to your skin. You cannot suddenly stop your sun exposure and expect all the damage to disappear and the cancer-causing effects of ultraviolet radiation are the result of many years of exposure.
UVB is the type of light which causes outdoor sunbathers to both tan and burn. The amount of UVB which the skin receives varies greatly depending upon the time of day and the season; it is most intense between 10 a.m. and 2 p.m. during the summer months. Ultraviolet B cannot penetrate window glass or heavy clouds, but it can penetrate light clouds. Because UVB only penetrates a small distance into the skin it has effects mainly in the outer layers of the skin (the epidermis) and is the most important cause of the two most common skin cancers, basal cell carcinoma and squamous cell carcinoma.
UVA does not vary much with time of day or season; you will receive as much UVA at 3 p.m. during the winter as you would at noon in the summer. UVA also penetrates window glass and clouds, so it will affect your skin from inside a car. Ultraviolet A penetrates deeper into the skin than UVB and affects both the outer layers of the skin (epidermis) and the deeper layers (dermis). Ultraviolet A radiation causes skin cancer, as does UVB, but its penetration deep into the dermis damages the collagen and elastic tissue and are a primary cause of wrinkles.
One of the notable aspects of modern life is the ability to be suntanned even in the depths of winter because of the use of tanning beds. The tanning industry has lured people into their businesses by touting the safety of tanning beds versus outside tanning and promoting the perception of tanned skin as attractive. The ugly truth is that tanning beds emit very intense UVA rays (far more intense than ever occur in nature) and people who tan frequently may receive as much as 12 times the annual UVA dose as those who tan outside in the sun. The intense UVA rays mean that people who use tanning beds regularly have a skin cancer risk as high, if not higher, than outside tanners and develop far more wrinkles, brown spots and other unsightly lesions. The incidence of melanoma skin cancer has been increasing steadily and is the second most common cancer seen in young adults aged 15-29 years, the age group which comprises 71 percent of the tanning bed users.
The bottom line is that there is no such thing as a ''healthy tan.'' The melanin pigment which allows your skin to look brown after repeated exposure to ultraviolet radiation is a protective reaction by your skin to prevent further damage to the cells of the epidermis. The only benefit to the body from UV exposure is the production of vitamin D in the skin, and the disadvantages far outweigh the advantages since vitamin D may be obtained through fortified foods and supplements.
Once you have made the commitment to protect your skin from the sun the question is: how do you do it? There are literally hundreds of sunscreens, hats, sunglasses and articles of clothing which claim to protect the skin from ultraviolet light. The first step to saving your skin is to learn to use sunscreens (also called sunblocks) correctly.
Sunscreens are topical products which prevent ultraviolet light from reaching your skin by either, 1) absorbing the UV light, or 2) by reflecting the light; these will be listed as the active ingredients on the sunscreen label. The first type protects the skin over only part of the ultraviolet spectrum, so the sunblock lotion must contain several different blockers to cover the entire range of dangerous rays. The second type, light reflecting sunscreens (sometimes called physical sunscreens), do not allow the UV rays to reach the skin, instead causing them to be reflected away. The two main physical blockers are zinc oxide and titanium dioxide. Zinc oxide has been used alone as a sunscreen for many years but is not popular because it is a thick white paste. Modern laboratory methods have succeeded in grinding zinc oxide into fine enough particles that it is invisible when used in a sunscreen.
The sun protection factor (SPF) is a number which indicates the amount of UVB protection a sunscreen provides and a 15 SPF is the minimum for a complete sunblock. Products with a 15 SPF block about 93 percent of the UVB rays, while a 30 SPF blocks 97 percent and a 50 SPF blocks 98 percent. When chemical sunscreens were first created they concentrated on protection from the UVB rays, which were known to cause sunburn and skin cancer, and the SPF was developed to allow consumers to choose wisely. Unfortunately, we now know that UVA is a significant cause of both wrinkling and skin cancer and many sunscreens advertise themselves as protecting from both, but there is not a number similar to the SPF to measure how well the UVA protection of a product works.
The Food and Drug Administration is now attempting to solve this problem by developing a measure for UVA protection. The effectiveness of a sunscreen is not dependent upon the form it is in: lotions, sprays and gels work equally well as long as the ingredients are correct. The best way to determine what sunblock to use is to visit The Skin Cancer Foundation Web site and check their guide to recommended products.
The most common cause of sunscreen failure (i.e., sunburning while using sunscreen) is the improper use of the product. The correct method of using sunscreen is:
1) Timing: Sunscreens must be put on 30 minutes before going outside to allow the product to soak into the skin. If you put it on when you are sweating or wet it will wash off before it goes to work.
2) Amount: Most people use far too little product to keep their skin protected. The correct amount of sunscreen to cover all the exposed areas is 1 ounce (2 tablespoons).
3) Reapplication: Sunscreen is washed off in water and by sweat and should be reapplied every two hours or after swimming or heavy sweating, even if it says it is waterproof or water resistant.
Special cases: Sunscreen should not be used in infants under 6 months of age because their skin is too sensitive; they should be kept out of the sun by using sunshades and other protective covers. For users who are allergic to sunscreen (which, ironically, usually shows up as a bad sunburn), or who are just sensitive and have stinging skin or eyes from their products, there are sunscreens available which have only titanium dioxide or zinc oxide, which are non-reactive with the skin. The one problem with these products is that they sit on the surface of the skin and can be wiped off if the skin is rubbed, so they are not good for many athletes, such as tennis players, who towel off the sweat between points.
Lips: The lower lip is a very common place for skin cancer, so don't forget to use lip balm with an SPF of at least 15, and reapply frequently, especially after eating.
These products, also called sunless tanners, contain dihydroxyacetone (DHA) which interacts with the keratin in the surface of the skin to form a golden brown color. These products are safe to use and are a good alternative to tanning in the sun. Just remember: they do not provide any sun protection and they can cause the skin to be an unsightly orange if overused. Self tanners gradually wear off as the outer cells of the skin naturally slough off. It is a good idea to exfoliate before using because if the outer layer of the skin is uneven and rough the tanner will not color evenly.
The protection of skin from the sun and the prevention of aging changes and skin cancers must go far beyond the use of sunscreens. It is critical for children to learn from birth to protect their skin and avoid painful and dangerous sunburns as well as the long-term cumulative damage which occurs from frequent exposure.
Sun protective hats must be tightly woven and should have a brim at least 3 inches wide, or have a ''foreign legion'' style back flap to protect the neck. Loosely woven or mesh hats do not offer much protection and baseball-style caps protect only the forehead and the upper part of the nose. It is important to protect the ears and the scalp; both of these areas are very prone to skin cancer and are often forgotten when applying sunscreen.
Improperly selected sunglasses may actually increase your risk of cataracts or retinal damage from the sun. Dark glasses tell your eyes that the pupil should open wider to allow more light into the eye and the thin plastic lenses in nonprescription sunglasses do not stop UV light. Sunglasses should be labeled to be at 98 percent UV protective or higher. The UV protection rate is usually on a sticker on the lenses of the glasses at the time of purchase. Prescription sunglasses can be coated to prevent UV penetration; see your optometrist for further information.
Clothing varies significantly in its ability to stop the sun from reaching skin. The traditional white T-shirt put on when swimming offers protection comparable to an SPF of 7; far below the needed 15 for full coverage. In general, clothing will be more protective if it is: 1) tightly woven, 2) a dark color, 3) heavier in weight, and 4) dry. The exception to these rules is shiny polyester or silk, which reflects the sun and thus may be more protective than heavier, darker fabrics. Several companies manufacture clothing specifically for sun protection, offering a variety of styles and colors. This clothing is rated with a UPF (ultraviolet protection factor) number which is similar to the SPF of sunscreens. Clothing must have a UPF of at least 15 to be considered adequate protection, but some may have UPFs as high as 50-plus. These clothes are usually made of light-weight, high-tech fabrics and are easy care. Some brand names, which are approved by the Skin Cancer Foundation include: Coolibar, Sun Busters, Solar Protective Factory and BTC Innovations, as well as the Columbia Sportwear Omni-Shade products.
Ordinary clothing can be made UV resistant by adding Sun Guard to laundry detergents. This additive contains the sunscreen Tinsorb(R)FD and will withstand up to 20 washings.
Ultraviolet blocking clear films are available for the windows of both cars and buildings. They block about 99 percent of the UV light coming through the windows and are offered in both clear and tints of varying darkness. These films have been used on auto windshields for some time, but are not standard on side windows. Note: most states have limits on how dark the tint may be on front and side windows in an automobile. In Iowa, the State Patrol officers have a meter, which they can use to check and make sure your windows comply with state law. Check with law enforcement and avoid a ticket before having films added to your car windows.
Schools and government bodies are finally becoming aware of the importance of sun protection for young children as well as adults and some are putting sunshades over playground equipment, bleachers, pool surrounds and occasionally even over sections of swimming pools. The sunshade structures decrease UV exposure from overhead and give significant relief from the heat, as well.
For further information: see the Skin Cancer Foundation Web site at www.skincancer.org.
Carey A. Bligard, M.D., is a dermatologist affiliated with the Trimark Physicians Group who has practiced in Fort Dodge for 21 years. She trained at The Johns Hopkins University School of Medicine and Tulane University Medical School. She is the Des Moines Health and Beauty Examiner for www.examiner.com.