In recent medical studies, some sunscreen ingredients have come under scrutiny for posing health risks. BMC Connection asked Deborah L. Cummins, M.D., director of Mohs and dermatologic surgery at Boston Medical Center, to talk about the benefits of sunscreen and the recent controversy surrounding it and to offer tips on choosing the safest sunblock this summer.
BMC Connection: First of all Dr. Cummins, why is it important to use sunblock? What are the dangers of sun exposure and how do sunscreens protect us?
Dr. Cummins: Ultraviolet (UV) light exposure from natural sunlight and tanning beds is a proven carcinogen that increases risk of skin cancers. UV exposure is the most preventable risk factor for skin cancer. Sunscreen use is one method to protect skin from the harmful effects of UV rays.
Sunscreens have been proven to prevent squamous cell carcinoma and actinic keratoses (pre-cancers). Sunscreens probably also protect against melanoma, the most deadly form of skin cancer. Mice studies have shown that sunscreens protect against melanoma. This phenomenon has been more difficult to prove in human studies because people who use sunscreen regularly often stay out in the sun longer. Dermatologists recommend that sunscreens should not be used as a means to allow longer sun exposure because sunscreens do not provide complete protection from the sun
BMC Connection: If sunscreen alone cannot protect against melanoma, what other precautions should people take to protect themselves?
Dr. Cummins: Physical barriers to sun (hats, protective clothing, shade, and remaining indoors during peak sun hours) have been proven to decrease risk of melanoma and other skin cancers. It is widely agreed that these are the most effective methods of sun protection. Sunscreens should be used in addition to these methods to protect sites such as face and arms that cannot conveniently be kept fully covered. Sunscreens should not be considered a substitute for these other forms of sun protection.
BMC Connection: What about sun protection factor (SPF) numbers, do higher numbers mean better UV protection?
Dr. Cummins: SPF does matter and generally higher SPF is preferable. However, studies indicate that SPF labels are not reliable. In reality, the sun protection afforded is only a small fraction of the SPF number listed on the sunscreen bottle due to several factors including breakdown of active ingredients, insufficient application and failure to reapply every two hours and after swimming. SPF is only half the story. SPF describes the level of UVB protection (UV light spectrum from 290 nm to 320 nm wavelengths). The sun’s UVA rays (320 nm to 400 nm) are also harmful and it is important to select a sunscreen that has broad-spectrum UVA coverage. At present there is no grading system to rate sunscreen UVA protection. A four star system for grading UVA protection is being considered by the Food and Drug Administration. Until that grading system is released, examination of active ingredients can help identify sunscreens with broad UVA protection. Agents that are broadly effective against UVA include titanium dioxide, zinc oxide, and avobenzone (parsol 1789). Mexoryl is particularly effective for short-wave UVA.
BMC Connection: There has been a lot in the news regarding the health risks of vitamin D deficiency. Since sun is the main source of vitamin D, do we lose out on this important nutrient by applying sunscreen? It seems like a Catch-22 situation.
Dr. Cummins: Vitamin D is produced with sun exposure and may result in better health. Although sunscreen and sun protection may lower vitamin D levels, it can be safely replenished with a vitamin D pill at a dose of approximately 1,000-2,000 IU daily. In this way, vitamin D levels can be optimized without exposure to the harmful UV light that causes skin cancers. Many physicians now include vitamin D levels among their routine screening labs to identify people who would most benefit from oral supplementation.
BMC Connection: There has been recent controversy surrounding ingredients in sunscreen. What exactly is the concern, and what should we be looking for in a safe sunscreen?
Dr. Cummins: The Environmental Working Group recently made headlines when they reported a potential risk associated with vitamin A derivatives such as retinyl palmitate (a common sunscreen additive). The concerns are based on an FDA study showing that lab rats coated in retinyl palmitate and exposed to light developed skin cancers up to 21% faster than similar rats without retinyl palmitate in their cream. It is unclear whether retinyl palmitate poses a risk to humans, but until more data is available, it may be wise to choose sunscreens without vitamin A derivatives.
In addition, titanium dioxide and zinc oxide sunscreens have been favored by many dermatologists due to broad-spectrum UV protection and stability. These agents work by physically blocking light in contrast to chemical sunscreens that undergo a chemical reaction to absorb light. However standard size titanium and zinc particles have an undesirable opaque white appearance when applied to the skin. For this reason, sunscreen manufacturers currently process titanium and zinc into nanoparticles (small particles measuring 1-100 nanometers), which makes the sunblock less opaque. Recently, concern has been raised because, due to their small size, nanoparticles can be absorbed from the skin into the body. It is not clear whether this absorption correlates with any true health risks and it is probable that the benefits from the excellent UV protection outweigh the theoretical risks of titanium and zinc absorption.
Oxybenzone can also be absorbed through the skin and may have hormonal effects. It is not clear whether this translates to actual health risks, but it would be reasonable to avoid this agent, particularly among pregnant women.