Ask the Doctor: How Does Sunlight Affect the Skin?
Q: How does sunlight affect the skin?
A: Sunlight deposits energy onto and into our skin. This energy comes to our skin’s surface through both visible and ultraviolet light (which is invisible). Scientists divide this light into three wavelength categories: UVA, UVB, and UVC. For the purpose of our discussion, our focus will center on UVA and UVB rays.
UVB rays are the shorter wavelengths (290 nanometers [nm] to 320 nm), and they don’t penetrate deeply into the skin. While they are the major cause of squamous cell carcinomas, they are effectively blocked by most sunscreens.
The longer and more dangerous wavelengths are the UVA rays (320 nm to 400 nm), which penetrate deeply into the skin. It takes a thousand times as much UVA exposure to cause a burn as UVB exposure, and UVA rays are sometimes referred to as the “tanning rays” because they generally don’t cause a sunburn like the UVB rays. My colleagues and I believe that the UVA rays, which are not properly blocked by existing sunscreens, are the primary cause of basal cell carcinomas and malicious melanoma.
Q: Is sun exposure the cause of skin damage and skin cancer?
A: As a practicing environmental dermatologist, I see firsthand how sunlight—the most obvious source of environmental damage to our bodies—not only causes collagen breakdown, premature aging of the skin, wrinkling, and brown spots, but is also the primary cause of skin cancer and its most deadly form—melanoma. Sadly, I’m also seeing a frightening increase in melanomas among teens and even preteens. Recently, two teens in particular actually developed lentigo maligna melanoma, a type of cancer that is normally only seen in individuals in their 40s and older who have had long-term exposure to the sun.
Q: What is the SPF, and how is it determined?
A: SPF stands for Sun Protection Factor, which describes the ratio of the time it takes a sunburn to develop with the respective sunscreen on, compared to how long it takes sunburn to develop without the sunscreen on. Since SPF only addresses UVB rays, however, the SPF ratings have created a dangerous misconception of sun protection in the minds of consumers. While the United States government is aware of this fatal flaw, no effective system of rating UVA coverage currently exists, and skin cancer statistics continue to climb.
Q: Is there such a thing as a “healthy tan?”
A: To me the term “healthy tan” is the deadliest of oxymorons. There is no such thing as a “healthy tan.” In addition, consumers are not aware that there is still no clear evidence that sunscreens block the malignant UVA rays, which leads to a misconception about their safety while using those products.
Q: Does sunscreen really protect against skin cancer?
A: A few years ago, the Australian government initiated a massive public service educational campaign called “Slip, Slop, Slap” to encourage the use of sunscreens. The campaign was a big success and boosted the per capita use of sunscreens there to record levels. On the heels of this campaign, researchers at the Queensland Institute for Medical Research in Brisbane followed 1,383 adults for five years and reported in 1999 that, while sunscreen use reduces the risk of developing squamous cell carcinoma, the use of sunscreens did not reduce the risk of developing melanomas or basal cell carcinomas.
Q: Since even the best sunscreens offer incomplete protection from the sun’s deadliest (UVA) rays, should we stop using them?
A: Absolutely not! Sunscreens should be used whenever one is outside, regardless of the season or temperature, and should always be applied on cloudy days as well as on sunny ones. Granted, these products are inadequate, but they do protect against UVB rays that cause sunburns and increase the risk of some skin cancers. The bottom line is that while sunscreens have disabled the body’s early-warning system—namely, sunburns—and have created a false, and dangerous, sense of security in the minds of consumers, they’re all we have for now. Therefore, we need to continue using them until science perfects a successful UVA sun-blocking solution, which I believe is near at hand.
Q: What are some practical tips to best protect myself and my family from sun damage and skin cancer?
A: Limit sun exposure and cover up as much as possible when you are outside. Always wear a hat, Polarized, UV-certified sunglasses, and sun-protective clothing whenever possible. Before applying a sunscreen, apply a topical antioxidant cream, such as vitamin E or vitamin C, to absorb or diffuse energy not blocked by the imperfect sunscreens. My own research, and patient feedback, has convinced me that antioxidant creams containing ellagitannins (found in raspberries, and other fruits) offer the greatest benefits when used in conjunction with a sunscreen. The ellagitannins not only have the ability to absorb excess energy but also may directly protect DNA.
Always use a waterproof sunscreen with a SPF of at least 30. Look for sunscreens containing the recently FDA-approved, UVA-blocking chemical Mexoryl, which, while also flawed, offers the best protection currently available. Apply the first application in a cool environment, as this decreases the chance of perspiration, thereby allowing the sunscreen to properly coat and adhere to the skin. Reapply the sunscreen at least every 90 minutes while outside. If you don’t want to use a chemical-based sunscreen, you can opt for invisible zinc oxide.