Uncovering the Controversies Which Cloud Sunscreen

January 7, 2011

There is much confusion surrounding the protective benefits of sunscreen. A noted dermatologist provides insight on this important segment.

THE PROTECTIVE benefit of sunscreens from UV radiation, a known carcinogen, is well established. However, important questions still surround sunscreens and several key ingredients. HAPPI recently sat down with Steven Q. Wang, MD, director of Dermatologic Surgery and Dermatology, Memorial Sloan- Kettering Cancer Center at Basking Ridge, NJ, to discuss the controversies surrounding sunscreens.

Happi: Regular sunscreen use has proved effective at reducing the development of both squamous cell cancers (SCC) and actinic keratoses. Have there been any studies that show a statistically significant protective benefit of sunscreen against either basal cell carcinoma (BCC) or malignant melanoma?

Wang: The evidence currently available indicates that regular sunscreen use provides prolonged protective benefit in preventing SCCs.

However, while there is no demonstrated benefit of regular sunscreen use in reducing the incidence of BCC development, a trend toward reduced incidence of BCC tumors among sunscreen users has been observed.

Steven Q. Wang
Furthermore, current data has demonstrated that sunscreens do not increase the risk of melanoma, but clinical evidence for its protective benefits remains inconclusive. However a publication in the Journal of Clinical Oncology in 2010 featured a study from Australia in which the investigators showed a 50% reduction of melanoma in individuals who used sunscreens. One important limitation of all the available clinical and epidemiological evidence, however, is that most of the studies were conducted during the 1970s and 1980s when only sunscreens with low SPF and little to no UVA protection were available. Modern sunscreens have corrected these shortcomings. However, long-term studies using these newer sunscreens are not yet available. Moreover, it may take many years or decades to determine the potential protective effects of improved sunscreen formulations. Thus, it is reasonable to conclude that in conjunction with better education, future studies using these sunscreens in a corrective manner may demonstrate a preventive effect for BCC and melanoma.

Happi: What about vitamin D? Does sunscreen use impair vitamin D production? Wang: Considerable overlap exists between the UV absorption profiles of sunscreens and the action spectrum for vitamin D synthesis. In theory, correct usage of sunscreens should significantly reduce vitamin D levels. However, this is not the case in practice. In fact, several studies have demonstrated that sunscreens are rarely applied correctly, in the right dosages and with appropriate frequency.

Therefore, under real-world conditions, it is likely that the improper use of sunscreen and/or increased exposure time results in normal production of vitamin D among sunscreen users. It is important to note that the level of cutaneous vitamin D production from UVB exposure is also influenced by seasons, latitude, obesity level and age.

Hence, after considering all these factors, we dermatologists prefer dietary supplementation, instead of prolonged UV exposure, to maintain the sufficient levels of vitamin D.

Happi: Regarding UV filters, is oxybenzone safe?

Wang: Systemic absorption of oxybenzone after topical application in both humans and animals has garnered significant attention. It is important to note that systemic absorption did not result in clinically significant perturbations of hormonal homeostasis in humans.

In fact, acute toxicity has not been reported in any of the in vivo or human studies published to date. While more work remains to be performed in this area, the available evidence does not demonstrate biologically significant hormonal disruption with topical application of oxybenzone in humans.

Happi: Retinyl palmitate has found widespread use in cosmetic and sunscreen products during the past 20 years. Earlier this year, there was a flurry of media coverage discussing the photocarcinogenic potential of sunscreens containing retinyl palmitate. Can you comment on this issue? Wang: It is important to understand that retinyl palmitate is the storage form of retinol (vitamin A), an essential and endogenous nutrient for human beings.

This compound is already present in our skin. All available evidence from in vitro and animal studies fails to demonstrate convincing evidence indicating that retinyl palmitate imparts an increased risk of skin cancer.

Although published data on the photocarcinogenic potential of retinyl palmitate in humans are lacking, evidence from 40 years of use in clinical medicine provide a powerful basis from which to question the notion that retinyl palmitate in sunscreen is photocarcinogenic. Clinically, retinoids are used by dermatologists in two major areas of therapy.

First, oral retinoids have been used with great success to prevent skin cancers in populations who are at high-risk, such as patients with xeroderma pigmentosum and immunosuppressed patients.

Second, dermatologists commonly prescribe topical retinoids in the management of skin disorders such as acne, psoriasis, photoaging, cutaneous T-cell lymphoma and a variety of other skin conditions. Among patients treated with topical or oral retinoids, no published data exists to date suggesting that these medications increase the risk of skin cancer.

Happi: Has the controversy surrounding nanoparticles heated up?

Wang: Nanoparticles exhibit different chemical, mechanical, electrical and optical properties than the standard-sized particles. Nano-scaled versions are postulated to also exhibit altered biological properties, which may have negative health implications. The recent integration of TiO2 and ZnO nanoparticles into sunscreens has raised interesting questions regarding the potential for dermal penetration, systemic absorption and subsequent toxicity. The increasing ubiquity of these nanocompounds in personal care and cosmetic products makes safety research especially relevant. Much concern has been voiced that the integration of nanomaterial technology into everyday formulations has outpaced the body of research evaluating their safety.

Currently, the FDA does not have regulations in place regarding the labeling of products containing nanoparticles of TiO2 and ZnO. Considerable data assessing the potential toxicity of these materials in sunscreens has been published to date, and studies were performed in controlled environments on healthy, undamaged skin. It has been established that the stratum corneum is an effective barrier preventing the entry of nano ZnO and TiO2 into deeper layers of the skin. Nonetheless, it remains to be determined whether a greater degree of penetration occurs through skin in conditions where the barrier function is damaged, or otherwise compromised. At the present time, however, the available data does not provide conclusive evidence demonstrating that damaged skin leads to increased penetration of nanoparticles.

Happi: So, what’s your prognosis on the use of sunscreens and their role in preventing skin cancer?

Wang: Sunscreens remain an effective tool in providing protection against the known carcinogenic effects of UV radiation. Sunscreens will continue to be a highly popular form of photoprotection in the foreseeable future.

As modern formulations of sunscreens grow increasingly more sophisticated, ongoing monitoring to assess both the safety and efficacy of these products is needed. Preferably, these assessments should be conducted under real-world conditions that reflect the actual behaviors of the general public.

Lastly, it is important to remember that sunscreen is only a part of the overall photoprotective strategy. We should also remind the public to avoid excessive UV exposure from the sun and wear hats and clothing for protection as well. • About the Author

Steven Q. Wang, MD, is a dermatologist practicing within the Dermatology Division at Memorial- Sloan Kettering Cancer Center, New York, NY. He can be reached at: wangs@mskcc.org

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