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July 30, 2017—New York—Sunscreen with SPF >50 is effective and important in reducing melanoma risk. The best formulation of sunscreen is the one that the patient will apply regularly as recommended.
These conclusions, based on a talk entitled, What's New in Sunscreen: What Your Patients Are Asking and Need to Know," were presented by Darrell S. Rigel, MD, MS, of New York University Medical Center.
He gave the talk at the 2017 American Academy of Dermatology Summer Meeting, which took place from July 27 – 30.
Epidemiology of Melanoma
More skin cancers occur than all other cancer combined in the US. Lifetime risk of invasive melanoma has risen from one in 1500 in 1930 to one in 50 in 2017. This risk is projected to rise to one in 40 by 2020. Though more than one American dies of melanoma every hour, deaths from melanoma dropped from 10,130 in 2017 to 9730 in 2017.
The lifetime risk of invasive melanoma among US males is one in 28, for females, one in 44. In 2017, 63,410 cases of in situ melanoma have been reported, and 87,100 cases of invasive disease. In 2017, 6% (n=52,170) of new cancers in males were melanoma, and 4% (n=34,940) of those in females.
Melanoma is one of the few cancers of which we know the cause—ultraviolet radiation exposure, and for which a simple behavioral change—minimization of ultraviolet light exposure—lowers risk.
The incidence of melanoma rises with proximity to the Equator, such that Hawaii is the most affected state in the US. Between 89% and 95% of annual cutaneous melanoma cases are caused by solar ultraviolet light exposure. Not all melanomas are caused by ultraviolet light exposure, but the vast majority are.
News on Sunscreen That Patients May Mention
In the third week of May, Consumer Reports and the Environmental Working Group issue updates on sunscreens. These updates are circulated in social media, peeking awareness and provoking questions to physicians.
In 2016, Consumer Reports rated 67 sunscreens categorized as chemical and mineral, chemical, and mineral. They stated that half the products were an SPF below that printed on the label.
In 2017, the Environmental Working Group reported that sunscreen spray sales exceeded lotions for the first time. They listed aerosol spray sunscreens with SPF >50 that contained the harmful additives oxybenzone and retinyl palmitate. The Environmental Working Group rated two products made by the Honest Company among the best beach and sport sunscreens, yet a lawsuit accused this startup of selling deceptively labeled products.
Websites of both Consumer Reports and the Environmental Working Group carry a link to Amazon.com to purchase the products. The Environmental Working Group states that it may receive a commission for purchases made via the Amazon.com link.
The Weight of Evidence in Favor of Regular Sunscreen Use
In a small study by Green et al. in 2011, regular sunscreen use was associated with reduced melanoma risk. A total of 1621 randomly selected residents of Queensland, Australia, age 25 – 75 years, were randomized to daily or discretionary sunscreen application to the head and arms. They were treated for 5 yeas and followed for 10 years. Only 11 new cases of malignant melanoma occurred in the daily group vs 22 in the discretionary group (P = .051). Of the 11 new melanomas, two were invasive. Dr. Green concluded that regular sunscreen use may reduce melanoma risk.
A 2015 study by Olsen et al. found that regular sunscreen use prevented skin cancers in Australia. Dr. Olsen estimated the proportion of skin cancers that would have occurred but were likely prevented by regular sunscreen use. Regular sunscreen use was estimated to have prevented approximately 14,190 persons from developing squamous cell carcinoma (prevented fraction 9.3%) and 1730 from melanoma (prevented fraction 14%). Dr. Olsen concluded that prevailing levels of sunscreen use probably reduced skin cancer incidence by 10%-15%, and that sunscreen should be a component of a comprehensive sun protection strategy.
A 2016 Norwegian study found that in women with blonde or red hair who freckled in the sun, using a sunscreen with SPF >15 was associated with significant improvement.
Waiting 15 – 20 minutes after sunscreen application, though mandatory on product labels, is not necessary. Ultraviolet protection is instantaneous. Reapplication after 2 h, also mandatory on labels, is not necessary but is advisable to assure a proper application level and to hit "missed spots."
Jung et al., in 2012, found that extended exposures to high temperatures can degrade sunscreen but a 2010 study by Rego et al found that sunscreen protection does not degrade at outdoor summer temperatures during a typical vacation period.
Are SPFs Higher Than 50 Worth the Extra Cost?
Sunscreens with SPF ≥50 are available in developed countries such as New Zealand, the US, and in Europe. Australia, among others, caps SPF at 50+.
Arguments in favor of capping SPF include containing the higher cost of the increased SPF formulations and the little marginal improvement in ultraviolet B protection that these products confer. The increase in ultraviolet B protection is only 1% from SFP 50 to SPF 100.
The argument against capping the products at SPF 50+ is that sunscreens with higher SPFs confer better protection at "real world" application concentrations. In addition, a 1979 study by Sayre et al found that SPF 15 sunscreens prevent 93.3% of ultraviolet B absorption, SPF 20 products prevent 96.7%, SPF 45 products prevent 97.8%, and SPF 50 products prevent 98%. These rates assume that sunscreen is applied at the tested concentration of 2 mg per square centimeter. Typically, only 25% to 50% of the rated amount is applied.
A 1997 study by Stokes et al. found that sunscreen is underused. Sunscreen application varies widely, with many individuals using less than the recommended 2 mg per square centimeter. Users were found to receive a mean SPF of 20%-50% of the expected amount due to inadequate application. Underprotection due to inadequate application may explain why sunscreen use has been reported in some studies to be a risk factor for melanoma.
Sunscreen SPF is tested using a thickness of 2 mg per square centimeter. Investigations show that sunscreen, under natural conditions, is applied insufficiently, at amounts approximately 0.39 to 1.0 mg per square centimeter. Other pitfalls that reduce the protective effect of sunscreens are missing areas and ultraviolet radiation exposure before sunscreen application.
Numerous studies have shown that consumers typically underapply sunscreen by ¼ to ½ of the recommended amount. They seldom reapply after the initial application, and not all body areas receive comprehensive application and coverage.
Whether high SPF compensates for underapplication of sunscreen was determined by Ou-Yang et al. in 2012. They measured the SPF values of various sunscreens from SPF 30 – 100 applied in the reduced amounts typically used by consumers. They found a linear relationship between application density and SPF delivered. Sunscreens labeled >50 SPF provided significant protection, even when applied at "real world" typical application densities.
Whether sunscreens with SPF >50 provide additional benefit was determined by Williams et al in an in vivo comparison of SPF 100 vs SPF 50 in "real world" conditions. They found that high-SPF sunscreen did provide significant clinical benefit in real world conditions, that sunscreen with SPF 100+ was more effective than that with SPF 50+.
In addition, Russak et al. found in 2010 that high-SPF formulations were more effective during intensive ultraviolet exposures. They tested a formulation containing SPF 85 vs one containing SPF 50 sunscreen. Fifty-six subjects applied sunscreen to the face while skiing in 2008.
They applied sunscreen only once at the start of the day and were exposed an average of 5.0 h. Seven of 28 sunburned with SPF 50 sunscreen vs one of 28 who applied SPF 85 sunscreen (P = .02). Dr. Russak concluded that the SPF 85 formulation was more effective than the SPF 50 formulation in protecting from sunburn after a single application in a high-ultraviolet test environment.
A study not yet published by Williams et al. took into consideration the facts that in real-world settings, consumers apply sunscreen at densities lower than those used to determine SPF clinically, and that the linear dependence of SPF to application density is well established. It hypothesized that a sunscreen with higher SPF would provide greater in-use efficacy than one labeled at the proposed maximum of SPF 50+. The objective was to evaluate the difference in sunburn protection provided by different SPF sunscreens during a day of skiing.
The split-face study compared SPF 100+ or SPF 50+ sunscreen lotion. Usage, application density, and reapplication frequency were comparable. After 6 h of sun exposure while skiing, SPF 100+ sunscreen was found to be significantly more effective at protecting against sunburn than SPF 50+ sunscreen. Erythema was significantly lower on the SPF 100+ protected side of the face, and erythema progression was observed to be more than twice as severe on the SPF 50+ protected side. The number of sunscreen reapplications was not observed to diminish the enhanced protection benefit of the SPF 100+ product.
Dr. Williams concluded that the SPF 100+ sunscreen was significantly more effective in protecting against sunburn than the SPF 50+ sunscreen, and that sunscreens labeled as SPF higher than 50+ are needed to provide consumers with better choices of sunburn protection.
A 2016 randomized, evaluator-blinded, controlled study by Ou-Yang et al. set out to measure sunburn protection offered by shade from a beach umbrella vs SPF 100 sunscreen for 3.5 h at a lakeside beach near Dallas, Texas. Subjects were reminded to reapply the sunscreen after 2 h.
The shaded group used a standard beach umbrella with an ultraviolet protection factor rating of 1000+. They wore no sunscreen and were reminded to reposition the umbrella as the solar angle changed.
The group wearing sunscreen experienced a significantly higher increase in sunburn to the face only (P < .05). The shaded group experienced a significant increase in sunburn to all body sites (P < .001). Seventy-eight percent of subjects in the shaded group had an increased sunburn score. Twenty-five percent of subjects in the sunscreen group had an increased sunburn score.
Dr. Ou-Yang concluded that the shaded group scored significantly higher in sunburn (P < .001), and that seeking shade alone may not provide sufficient protection during extended ultraviolet sun exposure. Neither shade nor high SPF sunscreen alone prevented sunburn completely. Dr. Ou-Yang suggested that multiple sun-protective measures be recommended rather than a single approach.
Retinyl Palmitate: An Ingredient Whose Safety Has Been Questioned
The safety of retinyl palmitate, a vitamin A analog cosmetic ingredient and antioxidant used in sunscreen, has been questioned. In 2010, Wang et al. proposed that no published evidence suggests that topical retinoids increased the risk of photocarcinogenesis. Retinyl palmitate has been used in topical agents for over 40 years. Retinoids are used for chemoprevention of skin cancer in persons at high risk, such as transplant population and patients with xeroderma pigmentosum, with no evidence of increased skin cancer risk.
Protection Against Photodamage Other Than Melanoma
To determine whether sunscreen protects against other photodamage, in 2014, Cole et al. evaluated whether high-SPF sunscreen can protect skin at the cellular level under ultraviolet exposure doses, similarly to the SPF value. Sunburn cells, Langerhans cells, thymic dimers, protein 53, and matrix metalloproteinase 1 and 9 endpoints were evaluated in biopsies from 12 subjects. They were either unprotected, and exposed to 0, 1, and 3 minimal erythema dose or had applied SPF 55 sunscreen and were exposed to 55 minimal erythema dose of ultraviolet radiation.
After 55 minimal erythema doses, sunscreen-protected sites showed either significantly less damage or no difference than the one minimal erythema dose – exposed unprotected sites. Dr. Cole concluded that high-SPF sunscreen with high ultraviolet A preventive factor can provide proportionately high protection against multiple cellular damage markers.
Hughes et al., in 2013, set out to evaluate sunscreen to prevent skin aging in a randomized trial. They were randomized to daily use of a broad spectrum sunscreen and 30 mg of beta-carotene, daily use of sunscreen and placebo, discretionary use of sunscreen and 30 mg of beta-carotene, or discretionary use of sunscreen and placebo.
Skin aging from baseline to conclusion was significantly less in the daily sunscreen group than in the discretionary group (odds ratio 0.76). Dr. Hughes concluded that regular sunscreen use retards skin aging in healthy, middle-age men and women. Beta-carotene was not shown to affect skin aging.
Nanoparticles vs Microsized Particles
In 2014, Singh et al. compared the sun protection of metal oxide nanoparticles vs conventional particles in an in vitro study. Nanoparticle formulations conferred better spreadability and better SPF values by a 2 x margin. Dr. Singh concluded that nanoparticles in sunscreen proved advantageous, conferring benefits of good texture, better spreadability, and enhanced in vitro SPF.
Borase et al., in 2014, found that gold nanoparticles are a potent alternative to traditionally used titanium oxide and zinc oxide nanoparticles in commercial sunscreens.
In 2011, Smijs et al. evaluated the safety and efficacy of titanium dioxide and zinc oxide nanoparticles vs microsized titanium dioxide and zinc oxide. The conclusion was that caution should be exercised when new sunscreens are developed because sunscreen nanoparticles induce (photo) cyto- and genotoxicity, which have been sporadically observed in viable skin layers.
Polypodium leucotomos
In 2013, Jansen et al. published an article on Polypodium leucotomos, a natural fern leaf extract with anti-inflammatory and antioxidant properties that is taken orally. Administration of oral P. leucotomos to a group of high-risk patients with malignant melanoma or dysplastic nevus syndrome led to a significant reduction in sensitivity to ultraviolet radiation in all patients. Other studies have found that oral administration of 480 – 1200 mg daily of this extract can prevent polymorphous light eruption lesions in patients with polymorphous light eruption.
P. leucotomos has been shown to reduce the known effects of ultraviolet radiation, including minimal erythema dose, minimal phototoxic dose, ultraviolet-induced epidermal proliferation, development of DNA damage, and reactive oxygen species. Studies published in 2004, 2013, and 2015 confirmed that the extract is effective for long-term use.
Changing Behavior
A 2014 study by Idorn et al. found that even patients diagnosed with cutaneous malignant melanoma failed to maintain long-term cautious sun behavior.
A 2013 evaluation of trends in physicians' sunscreen recommendations over a 21-year period, by Akamine et al., found that physicians mentioned sunscreen in one in 60 visits, and 86% of these mentions were by dermatologists. Even they mentioned sunscreen in only 1.6% of visits.
In 2013, Dennis et al. examined artificial ultraviolet use prior to vacation to protect against vacation-related sunburn. Tanning using an artificial ultraviolet source during the 10 weeks prior to vacation was not associated with reduced risk of sunburn during the vacation, but rather with an increase in this risk. Dr. Dennis concluded that maintaining a tan may not protect against sunburn, and that public health messages need to address this misconception.
Photoprotection in Car Windows
Wachler, in 2016, assessed levels of ultraviolet A protection in automobile windshields and side windows. The average percentage of front-windshield ultraviolet A blockage was 96% (range 95% - 98%) and side window blockage was 71% (range 445 – 96%). Dr. Wachler concluded that the results may in part explain the reported increased rates of cataract in left eyes and left-sided facial skin cancer.
Photoprotection and DEET Insect Repellant
Yiin et al., in 2014, assessed dermal absorption of DEET-containing insect repellant and oxybenzone-containing sunscreen, amid concerns about oxybenzones increasing the dermal absorption of DEET. The goal was to determine the best way to use these two products concurrently without extra absorption of either. Dr. Yiin confirmed enhanced DEET absorption when oxybenzone is applied after DEET. Applying the oxybenzone-containing sunscreen first, and then the insect repellant, with a 15-minute interval between the two applications, was recommended.
Conclusions
Dr. Rigel concluded that physicians need to learn what their patients are hearing about sun protection and have answers ready. When patients ask about photoprotection, clinicians need to assert that it is important and lowers melanoma risk. Sunscreens with SPF >50 are effective. Though many questions remain unanswered, new formulations are evolving with new agents and ingredients. The best sunscreen is the one that a patient will use regularly.
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Benjamin Hidalgo-Matlock
posted by dermatica at
August 03, 2017
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