by Warwick L. Morison, MD, MB, and Steve Q. Wang, MD
Drs. Morison and Wang, members of The Skin Cancer Foundation’s Photobiology Committee, address some recent concerns over sunscreen safety. The Photobiology Committee is a volunteer committee of photobiologists — experts on the interaction of ultraviolet (UV) radiation and the skin. Dr. Morison, committee chairman, is Professor of Dermatology, Johns Hopkins Medical School at Green Spring Station, MD. Dr. Wang is Director of Dermatologic Surgery and Dermatology, Memorial Sloan-Kettering Cancer Center in Basking Ridge, NJ.
About 90 percent of all skin cancers are associated with exposure to the sun’s harmful radiation,1 and sunscreen is one of the key strategies that helps prevent excessive exposure. When used as directed (applying one ounce to the entire body 30 minutes prior to going outside, and reapplying every two hours outdoors or immediately after swimming or sweating heavily), it can reduce the risk of actinic keratosis,2 the most common skin precancer, and squamous cell carcinoma,3 the second most common skin cancer, which affects an estimated 700,000 people in the US annually.4 In 2010, new research showed that sunscreen also helps protect against melanoma, the deadliest form of skin cancer. These benefits notwithstanding, ongoing media attacks have prompted some consumers to question sunscreen safety.
Sunscreen and Melanoma
You may have heard rumors that instead of protecting against melanoma, sunscreen actually causes the disease. However, comprehensive review of all studies from 1966 to 2003 found no evidence that sunscreen increases melanoma risk.5,6
In fact, recent research shows more convincingly than ever that sunscreen protects against melanoma. This past December, a groundbreaking study of 1,621 Australians found that regular sunscreen users reduced their incidence of melanoma by 50-73 percent.7 Earlier “retrospective” studies of sunscreen use, relying on people’s memories, pointed to a protective benefit, but this landmark “prospective, randomized” trial in humans is the first to show a significant and definitive benefit.
Sunscreen and Vitamin D Deficiency
Similarly, assertions that sunscreen use induces vitamin D deficiency, leaving us vulnerable to cancers and other medical problems, are unproven. vitamin D is essential for strong bones and a healthy immune system, but a recent review of 1,000 studies by the Institute of Medicine (IOM) in Washington, DC, determined that the vast majority of Americans take in enough vitamin D ,and found no sound evidence that vitamin D insufficiency is currently leading to cancers, heart disease, diabetes, or other conditions.8
Because the human body produces some vitamin D in response to the sun’s UV radiation, sunscreen use could in theory reduce vitamin D levels. However, several studies have found that subjects’ regular sunscreen use did not prevent adequate vitamin D intake. 9,10 It is also important to note that our bodies can manufacture only a certain amount of vitamin D from the sun. After reaching this limit within minutes, further UV exposure has a reverse effect, breaking down vitamin D into inactive compounds.11,12,13,14
The health risks of UV exposure — including skin cancer and premature skin aging — are great, and except for bone loss, far better proven than the suggested dangers of vitamin D insufficiency. The Skin Cancer Foundation advises children and adults under age 70 to obtain the IOM’s recommended daily 600 IU (international units) of vitamin D a day from foods such as oily fish, fortified dairy products and cereals, and supplements. Four hundred IU of vitamin D is an appropriate dose for infants under 12 months old, and 800 are recommended for people 70 and older. 15
A synthetic estrogen, oxybenzone is a chemical filter present in US sun- screens since the early 1980s. Some studies have demonstrated that it can penetrate the skin, interfering with hormone levels. 16 However, a 2004 study found that oxybenzone did not cause significant hormone disruption in humans. 17
Much of the concern stemmed from a 2001 study which found that 21-day- old rats fed 1,500+ mg of oxybenzone per kilogram a day — an astronomically high dose — had a 23 percent increase in uterine weight. 18,19 But what holds true in rat studies often does not end up applying to humans. Indeed, no evidence has shown that oxybenzone has any adverse health effect in humans.
Though oxybenzone is absorbed by the body, it does not accumulate — it is excreted, making significant buildup virtually impossible. The ingredient is FDA-approved for human use based on exhaustive review. The Skin Cancer Foundation’s Photobiology Committee reviewed the studies as well, finding no basis for concern about the use of sunscreens containing oxybenzone.
Retinyl palmitate, screen ingredient in trace amounts, is the form of vitamin A stored by the skin. vitamin A is an essential nutrient, and the National Institutes of Health’s Office of Dietary Supplements recommends that adults obtain 3,000to 4,300 International Units (IU) a day. 20
Several studies suggest that when exposed to UV radiation, retinyl palmitate generates free radicals, 21,22 chemically reactive substances whose interactions with DNA may cause mutations leading to cancer.
However, these studies have examined retinyl palmitate only as it reacts to U V radiation in isolation. In practice, when a sunscreen with retinyl palmitate is applied to the skin, antioxidants like vitamins C and E present in the body can neutralize free radicals. 23
Bottom line: There is no scientific evidence that retinyl palmitate causes cancer in humans. The research that generated the controversy is an unpublished 10-year-old study in mice, 24 far from proof of anything in humans. In fact, retinoids (topical vitamin A products similar to retinyl palmitate) are commonly prescribed by dermatologists, and no published data suggests that topical retinoids increase skin cancer risk.19 Oral retinoids are often prescribed to help prevent skin cancers in people at high risk of the disease!25,26
Titanium dioxide and zinc oxide are physical sunscreens with a long history of use, and considered two of the most protective broad-spectrum ingredients. They are comprised of large particles, which, in traditional sunscreen formulations, showed up on the skin as a thick, white paste. By minimizing, or “micronizing,” the size of sunscreen particles, the ingredients’ characteristic opacity is reduced, giving the skin a much more natural appearance. As nanoparticles (a nanometer is one billionth of a meter; nanoparticles are from 1 to 100 nanometers), zinc oxide and titanium dioxide offer the ingredients’ sun protection abilities with a more appealing cosmetic appearance.
The concern is that nanoparticles can be absorbed by the skin and harm living skin tissue. However, current research indicates that fears about absorption are unwarranted: Sunscreen is applied to the stratum corneum, the outermost layer of skin, which is made up of dead cells, and multiple studies have shown that nanoparticles do not penetrate living skin.27,28,29,30,31,32 Additionally, in sunscreen formulas, it appears that nanoparticles tend to clump together to form larger-than-nano-sized particles.
The safety of sunscreens has now been studied in labs and on live subjects by research scientists for years, and the evidence that sunscreens are safe and effective is overwhelming. We urge you to protect yourself from the sun using all the basic sun protection strategies — including shade, long clothing, UV-blocking sunglasses, wide-brimmed hats, and sunscreen.
Dr. Morison is Professor of Dermatology, Johns Hopkins University at Green Spring Station, Lutherville, MD, and chairman of The Skin Cancer Foundation’s Photobiology Committee. Dr. Morison has published more than 130 original papers in journals and is an author of two textbooks and over 30 chapters. He directs training courses in photomedicine and has been an invited speaker at many national and international meetings in his specialty.
Dr. Wang is Director of Dermatologic Surgery and Dermatology, Memorial Sloan-Kettering Cancer Center at Basking Ridge, NJ. A member of The Skin Cancer Foundation’s Photobiology Committee and the International Affairs Committee of the American Academy of Dermatology, he specializes in the diagnosis, treatment, and prevention of skin cancers, especially melanoma. Dr. Wang is actively involved in clinical research, with a focus on photo protection and the development of non- invasive imaging technologies to diagnose skin cancer. He has authored more than 50 publications in peer-reviewed scientific journals and academic textbooks. He is also the author of the book Beating Melanoma—A Five-Step Survival guide, published by Johns Hopkins University Press.
Published on November 17, 2011
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