The Sunscreen ParadoxPopular Misconceptions About Skin Cancer PreventionJune 2006
By Steven V. Joyal, MD
People apply sunscreen to protect against sunburn, skin aging, and skin cancer. Because of the way sunscreen products are labeled by FDA mandate, consumers are often confused about which ingredients they need to achieve optimal protection against the sun’s damaging and deadly rays.
Fortunately, scientific data have emerged indicating that health-conscious individuals can achieve broad-spectrum protection against the increasing onslaught of ultraviolet light penetrating our atmosphere.
Like clockwork, the sound bites occur on television news programs at the start of the summer season:
“To prevent skin cancer and premature aging of the skin, apply sunscreen before going out in the sun.”
Well known to scientists, physicians, and the average person alike, sun exposure is the main environmental risk factor for skin cancer,1 and sunburn is a well-established risk factor for skin cancer.2
Sun exposure in the form of ultraviolet light not only accelerates skin aging, but can also result in debilitating disfigurement from skin cancer. Some types of skin cancer can even lead to premature death. Furthermore, we are in the midst of a veritable epidemic of skin cancer. The incidence of basal and squamous cell carcinoma is increasing, as is the occurrence of deadly malignant melanoma, a dangerous form of skin cancer that develops in the pigment-producing cells of the skin, known as melanocytes.
Conventional wisdom indicates that, in addition to avoiding sun exposure, sunscreen is your best bet for preventing skin cancer. However, the sun protection factor (SPF) rating system used by the FDA to regulate sunscreen products has an inherent flaw that renders its ratings dangerously inaccurate. This may create a false and potentially disastrous sense of security in sunscreen users.
Flaws in the SPF Rating System
Basal cell and squamous cell skin cancers are caused primarily by a particular spectrum of sunlight called ultraviolet B, or UV-B. It is UV-B radiation that also causes sunburn. The FDA’s SPF rating system rates sunscreen for protection against UV-B light, but not against ultraviolet A (UV-A) light.
UV-A, the longer-wavelength ultraviolet light, penetrates deeper than UV-B through the outer portion of the skin. This is very important, because UV-A damage is largely responsible for premature aging of the skin. Moreover, UV-A light exposes the melanocytes, which are the pigment-producing cells in the skin, to damage that can potentially result in malignant melanoma, the deadliest form of skin cancer.
Thus, despite slathering on sunscreen and not developing a sunburn (because of protection against burning UV-B rays), we can still develop a light tan because the UV-A rays are penetrating the skin.
To protect your skin, you need broad-spectrum protection against both UV-A and UV-B rays. You cannot rely solely on the SPF rating system, because it provides information only on UV-B protection.
The only way to be sure that your sunscreen provides UV-A protection is to read the label and make sure it contains effective UV-A blocking agents, which include avobenzone, oxybenzone, zinc oxide, and/or titanium oxide.
Sunscreens, Topical Antioxidants, and Free Radical Damage
No matter what the ads promise, sunscreens alone inadequately protect against sunlight’s damaging, free radical-generating effects. In a study using special techniques to detect free radical damage to human skin after ultraviolet light exposure, application of conventional sunscreen with an SPF of 20+ resulted in a “free radical protection factor” of only 2!5
Ultraviolet light generates harmful free radicals such as the superoxide anion radical, hydrogen peroxide, the hydroxyl radical, and singlet oxygen, in addition to lipid peroxides.6
Studies demonstrate the critical importance of topical antioxidant protection to quench the free radicals generated by UV light that sunscreens miss. For example, adding simple antioxidants like vitamin E acetate and sodium ascorbyl phosphate (a stable form of vitamin C used topically) to a conventional sunscreen formula can decrease free radicals in the skin better than sunscreen alone.7 In addition, when antioxidants are combined with conventional sunscreen, greater-than-expected protection is achieved against sun damage.8
Vitamin D and Cancer Protection
Epidemiological studies suggest that sunlight exposure is associated with a decreased risk of non-Hodgkin’s lymphoma, a type of cancer of the lymph glands.14,15 Such studies also suggest that ultraviolet light exposure is associated with a lower risk of developing breast, colon, endometrial, esophageal, and ovarian cancer.16 Furthermore, death rates from cancers of the breast, prostate, and colon are higher in northern latitudes (which receive less sun exposure) than in southern latitudes (which enjoy relatively greater sun exposure).17
The question, then, is how could sunlight protect against cancer?
Vitamin D, synthesized in your skin after exposure to UV-B light, has a number of documented anti-cancer effects, including inhibiting cancer cell growth and promoting normal cell cycle activity.18-20
Interestingly, the active form of vitamin D generated by sun exposure on the skin—1,25-dihydroxyvitamin D3—is low in patients with malignant melanoma, the deadliest of skin cancers.21 Melanoma cell lines express the vitamin D receptor, and 1,25-dihydroxyvitamin D3 acts to decrease cancer cell growth as well as push the cell toward a more mature cell form. Medical scientists know that more immature cell types are seen with cancers that are more aggressive.
Although a very controversial idea, exposure to natural sunlight may be protective against melanoma. Recall that UV-B rays stimulate vitamin D in the skin, and vitamin D is likely protective against melanoma. Remember, too, that sunscreens that block UV-B but not UV-A rays will also block vitamin D production in the skin. This may be a deadly double whammy: no synthesis of protective vitamin D in the skin, yet exposure to the deeply penetrating UV-A rays.
A Risk/Benefit Approach to Sun Exposure
Given all the information available, what is the best sun exposure strategy—one that balances the risks and potential benefits?
As individuals, we each have a very different tolerance for sunlight exposure. For example, equatorial Africans have a much higher degree of natural protection from the sun than do people of northern European ancestry. In addition, there are many hypotheses in alternative medical circles regarding potential links between skin cancer and dietary overconsumption of omega-6 fatty acids, inadequate hormone status, and other factors. There may very well be some validity to such theories, but until more is known, the best strategy is to be prudent with regard to sun exposure.
This means that for many of us, brief exposure to sunlight (10-15 minutes, two to three times weekly) should allow adequate time for vitamin D synthesis by the skin, without greatly increasing the risk of skin cancer.22 Additional supplemental vitamin D (for example, 800 IU a day and higher) will be needed, however, because this short duration of UV-B exposure is unlikely to be sufficient for optimizing vitamin D status.
For people of northern European ancestry or those looking to minimize premature skin aging, sun exposure beyond 10-15 minutes should be accompanied by liberal application of a sunscreen with broad UV-spectrum protection and generous use of topical agents with demonstrated protective effects against free radical damage.