Susan Swetter, MD is a professor of dermatology and director of the Stanford Pigmented Lesion and Melanoma Program. BeWell recently asked Dr. Swetter to clear up some of the confusion about the effects of sun exposure and available methods of protection and cancer prevention.
What does the layperson need to know about UVA and UVB rays?
Ultraviolet (UV) radiation rays are responsible for sunburn, skin cancer, and “photoaging” (accelerated aging of the skin). Approximately 95% of UV radiation is comprised of UVA type rays, which are strong all day and all year long. The other 5% are UVB type rays, which penetrate the skin less deeply but are 400 times more intense in the summer and in the mid-day hours between 10 a.m. and 4 p.m. UVB rays play the largest role in causing sunburn and skin cancer, although UVA rays have more recently been linked to skin cancer and photoaging.
Who is at risk for skin cancer?
One in five Americans will develop skin cancer in their lifetimes, with the nonmelanoma skin cancer types (basal cell and squamous cell carcinoma) predominating. Melanoma is the most deadly form of skin cancer, accounting for only 4% of cases but over 80% of skin cancer deaths. People with fair skin (skin types 1 and 2 on the Fitzpatrick skin phototype scale) and those with increased numbers of common and atypical moles, sun sensitivity or family history are more likely to develop melanoma. Older men have the highest incidence and mortality rates from melanoma, although the number of new cases in young women is on the rise — likely related to tanning bed use.
Buying sunscreen can be so confusing. What should I look for?
The new FDA regulations have resulted in a big change as well as relabeling of sunscreen products, which must filter out the entire range of UVB and UVA wavelengths to be labeled as “broad spectrum.” Effective UVB filters have been available for many years and are measured by the sun protection factor (SPF). Full UVA filtration has been harder to achieve, and in the US, sunscreens that contain a chemical called avobenzone that is photostabilized with octocrylene provide the best UVA protection. Other UVA filters may be more effective but are not yet available in the U.S.
What is the biggest mistake people make with sunscreen?
Insufficient application is the most common mistake. Consumers use only about one-fourth to half of the sunscreen they need to achieve the SPF level that is actually contained in the product. For this reason, it may be more useful to apply a higher SPF-containing sunscreen (30 or above) or simply increase the amount you are putting on your skin. The key is finding a brand you like and using it regularly. A good rule is to use about 2 to 3 tablespoons for your body and 1 tablespoon for your face and to reapply every 2-4 hours. Remember, there is no such thing as a waterproof sunscreen, although sunscreens will soon be rated as either water resistant or very water resistant depending on how well they maintain their SPF level after water immersion. You can apply sunscreen just before you go outside, but you don’t want to put it on and jump right in the pool.
What about Vitamin D exposure?
The Vitamin D controversy has been overblown by the tanning industry, with some companies suggesting that seeking a tan (by artificial or natural UV light) is good for you. Incidental sunlight is likely adequate for sufficient vitamin D levels in most fair-complexioned individuals. Vitamin D supplementation is definitely safer than exposing yourself to excessive UV radiation to increase you blood levels of vitamin D, and there are guidelines for how much vitamin D to take published by the Institute of Medicine.
How do you convince the skeptic that sunscreen is worth the effort?
In 2010, the first prospective randomized trial was published that showed that daily use of sunscreen reduced the risk of melanoma by 50% compared with optional use of sunscreen. The benefits of sunscreen and sun protection in general (including avoidance of mid-day sun and tanning practices, and wearing hats, protective clothing and sunglasses) are well-established in terms of reducing the photoaging process and preventing skin cancer.
Interview conducted by Julie Croteau and edited by Lane McKenna Ryan.