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Researchers in the US found that the application of moisturiser to mice following sun exposure led to a higher incidence of skin cancer tumour formation. A number of ingredients in the moisturisers were identified as possible causes of the higher rate of tumour formation, but the authors indicated that similar findings have not been established in humans.
Prof Brian Diffey, Emeritus Professor of Photobiology in Dermatological Sciences at the Institute of Cellular Medicine, Newcastle University, said:
“This appears to be a well-designed and executed study and I have no issue with the findings. However, in extrapolating these results with regard to human use of moisturisers, I would make the following observations.
“The UV source used to pre-sensitise the mice is a very poor surrogate for sun exposure as it contains far too much UVB and UVC radiation compared with terrestrial sunlight. The dose regime of 30 mJ/cm2 twice a week for 20 weeks followed by no further UV exposure is nothing like the exposure that people receive during the course of their normal lives. Consequently quite what impact this particular spectrum of radiation and dose regime had on the subsequent tumour-developing activity and whether similar results would have been seen if a better match to the spectral and temporal nature of human sun exposure had been used remains unknown.
“Having said this, I am not dismissing the obvious extrapolation of their findings and if some constituents of moisturising creams are carcinogenic in humans, further work needs to be done to evaluate the real risk (as opposed to the hazard). To be fair, the authors do not overstate their findings, as you can see from the final 2 sentences: “It should be emphasized that our study as well as the other studies described here were only done in hairless SKH-1 mice, and their significance for humans has not been established. Further studies are needed to determine the effects of the widespread use of moisturizing creams on the risk of sunlight-induced skin cancer in humans.”
“A small point. In the Introduction they say: “The incidence of these cancers is increasing, which is believed to be caused by…and the depletion of the atmospheric ozone layer”. This is simply not true and is a widely-held myth. Ozone layer depletion has had a negligible impact on the increasing incidence of skin cancers seen over past decades and will probably have a very small impact in the future.”
Prof Jonathan Rees, Grant Chair of Dermatology at the University of Edinburgh, said:
“Non melanoma skin cancer in man is very, very common and is almost 100% curable with an operation usually simpler than a tooth filling.
“Studies of mouse skin cancer have contributed little to our understanding of human skin cancer. Mice are covered in hair, have really thin skin, and live in the dark: humans are largely bald, are designed for sun exposure and have comparatively much thicker skin. Extrapolation between the species for this aspect of biology is simply not warranted. For instance, it is well known that many agents that cause skin cancer in mice do not do so in man – indeed some of these agents are used as therapies. When contrasted with the known biology of human skin cancer and the pattern of human skin cream use, it seems to me extraordinarily unlikely that the presented results have any clinical relevance. I think it would be crazy to alter behaviour because of this one-off study.”
Prof J. Gordon McVie, Senior Consultant at the European Institute of Oncology and managing editor of ecancermedicalscience.com, said:
“A question mark about the safety of some moisturising creams has recently been raised in the light of an article in the Journal of Investigative Dermatology. There is no evidence of danger to humans in this study, but the message to scientists is clear. Be careful in assuming that seemingly inert creams will have no interference with animal experiments.
“The authors were interested in developing a cream or ointment containing caffeine to test whether it might protect against sunlight damage (and skin cancer) in humans. There is reasonable evidence from experiments in the lab which involve cells grown in the test tube, that caffeine might be helpful. As good authors should, they checked that the creams which would be used to carry the caffeine thro’ the skin in animal tests would not change the cancer model. But it seemed that they might do just that! Using only one type of mouse (called albino because it has no hair) the scientists started to expose the 2 month old baby animals to ultraviolet light daily over 17 weeks. This does not cause tumours on the skin at that moment, but if animals are observed for several months thereafter, some will develop skin cancers of the type which is not melanoma (i.e. the ones that are least aggressive).
If the animals were given daily moisturising creams or ointments after the end of ultraviolet light exposure, more got skin cancers. This has no relevance to causation of human skin cancer, and does not prove in any way whatever that moisturising creams are cancer-causing in humans. Many more studies now require to be done to follow up this unplanned and inexplicable test result.”
Prof Karol Sikora, Medical Director of Cancer Partners UK, said:
“This is a pretty artificial situation with the mouse skin primed by a lot of UV light to develop cancer. The differences between the various creams applied are actually very small. There is still a lot of controversy about sunlight and skin cancer – see this week’s BMJ correspondence on www.bmj.com so on balance I would still use sun creams!”