American Academy of Dermatology members say there is no evidence that the use of vitamin A in sunscreens causes cancer, contrary to a warning in the Environmental Working Group's latest sunscreen report.

In their report published online in the Journal of the AAD, the doctors note there are no published human data on the photocarcinogenic potential of sunscreens containing vitamin A, or retinyl palmitate, and laboratory studies offer no conclusive evidence to merit concern.

In an Aug. 10 release, report co-author Henry W. Lim, who practices at Henry Ford Hospital in Detroit, explains why the dermatologists weighed in on the matter.

EWG's health warning "garnered significant media attention and caused considerable confusion among the public," he says. "Our report should help dismiss the misinformation that sunscreens are not safe, as sunscreens are vitally important in reducing your risk for skin cancer, not causing it."

Docs Question Data Extrapolation

In its 2010 sunscreen report published in May, EWG suggests RP, present in 41 percent of sunscreens, may be photocarcinogenic. The public health watchdog advises consumers to choose sunscreens that do not contain the ingredient. The group's report got the attention of Sen. Charles E. Schumer, D-N.Y., who urged FDA to look into the issue (¹ 'The Tan Sheet' June 21, 2010, In Brief).

EWG's concerns are based mainly on preliminary data from a large animal study conducted by the National Institute of Environmental Health Sciences' National Toxicology Program. The findings have not yet undergone a scientific peer review.

RP was chosen for NTP testing in 2000 because of its widespread use in cosmetics and sunscreen products - not because it is necessarily dangerous or unsafe, note the authors including Lim and Steven Q. Wang of the Memorial Sloan-Kettering Cancer Center in New York, in their analysis. Aloe vera and nanoscale sunscreen actives titanium dioxide and zinc oxide also are under review, they point out.

The NTP study followed eight groups of hairless mice that were covered with varying concentrations of topical RP - 0.5 percent, 0.1 percent or placebo - and exposed to high or low doses of UV radiation to determine if a relationship exists between tumor development and RP in the presence of UV.

In the groups exposed to low doses of radiation, mice coated with 0.1 percent and 0.5 percent concentrations of RP both experienced higher instances of malignant lesions than the control group, but only the 0.5 percent group showed a statistically significant difference.

Furthermore, among mice receiving higher doses of radiation, there was no statistically significant difference in the incidence of malignant tumors between the control group and animals treated with either concentration of topical RP.

"Therefore, there is no conclusive evidence to indicate that the combination of RP and UV is photocarcinogenic," Wang, Lim and their colleagues reason.

They say "it is important to note that the mice in the NTP study are highly susceptible to the effects of UV radiation and can develop skin cancer or other skin abnormalities within weeks of UV exposure, even in the absence of retinyl palmitate."

Indeed, 38 percent and 82 percent of mice assigned to just the vehicle - a pH 7 cream without RP - developed malignant skin lesions when exposed to low and high radiation doses, respectively. The authors note that "mouse epidermis is significantly thinner than that of human beings, hence resulting in higher percutaneous absorption."

Overall, "extreme caution is needed when extrapolating these animal study results to human beings," they say.

In the absence of human clinical data, "observations from clinical medicine over the past four decades" should help to assure consumers of the safety of sunscreens containing RP, according to the researchers.

They point out that dermatologists routinely prescribe topical and oral retinoids to treat skin conditions such as acne and psoriasis, and there is no published evidence that the retinoids increase the risk of skin cancer in those patients. Oral retinoids are also used to prevent skin cancers in high-risk individuals such as organ transplant patients, without any demonstrated adverse outcomes.

"The bottom line is that people should continue vigilantly using sunscreens along with other sun-safe practices - such as limiting sun exposure, seeking shade, and wearing sun-protective clothing, hats and sunglasses - to reduce the risk of skin cancer and premature aging," say Wang, Lim and their team.

The authors were concerned because EWG's report, they say, "has resulted in many individuals questioning the overall safety of sunscreens, and with some expressing strong reluctance to use sunscreens for photoprotection."

In Vitro Studies Also Give Limited Picture

The Personal Care Product Council's Chief Scientist John Bailey remarked in May that "no credible scientific organization would ever evaluate such preliminary data [as NTP's] and make recommendations based upon it." At the time, EWG maintained that it was "comfortable" with the data and cited "15 other studies" published by federal agencies that have raised concerns about retinols.

Wang and Lim's team looked at eight in vitro and three smaller mice studies published by FDA between 2002 and 2009 on RP and UV exposure. Development of skin cancer was not reported in any of the mice studies. Researchers in the in vitro studies did observe photomutagenic effects and the creation of reactive oxygen species, which can cause cellular damage.

However, "the biological relevance of these findings in human beings is unclear," Wang and his colleagues say. They note that vitamin A can help to prevent damage from reactive oxygen species when it is able to cooperate with other elements in the antioxidant system.

"When a sunscreen with RP is applied to human skin, a full profile of non-enzymatic and enzymatic antioxidants are available to mitigate the risk of the pro-oxidative state seen in these in vitro experiments, where RP is the only antioxidant present in the experimental system," they say.

- Suzanne Blecher ( ² s.blecher@elsevier.com )

Dermatologists Find No Evidence That Vitamin A Sunscreens Cause Cancer

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