Friday August 15 2008
Continue to moisturise
Extensive and apparently conflicting media coverage has been given to a study on moisturisers and risk of skin cancer. The newspapers vary in their reports of the significance of the study, which involved applying moisturiser to irradiated, hairless, laboratory mice. The Independent said that moisturisers used by millions of people may be increasing the risk of common skin cancer. The Guardian said that women who use moisturisers should not be alarmed, and that if the effect were true for humans more of these cancers would occur in parts of the body where moisturisers are commonly applied and in women, which is not the case. The Daily Mail said the researchers had “cautioned that the experiments were carried out on mice”, but added “the majority of moisturisers have not gone through skin cancer safety checks”.
Although this study found that several commercially available moisturising creams increased the number and rate at which tumours formed, the research was in laboratory mice, and as the researchers acknowledge, mouse skin is different to human skin. Whichever way the relevance of this animal study is interpreted, for now it seems wise not to read too much into the results, to continue using moisturiser as usual and to wait for reliable research in humans.
Where did the story come from?
Dr Yao-Ping Lu and colleagues from the Susan Lehman Cullman Laboratory for Cancer Research at the Ernest Mario School of Pharmacy in New Jersey, USA, and colleagues from Cancer Institute in New Jersey and other universities, conducted the research. The study was supported in part by a grant from the National Institutes of Health and was published in the (peer-reviewed) medical journal: Journal of Investigative Dermatology.
What kind of scientific study was this?
This is an animal study conducted on 270 specially bred female albino hairless mice known as SKH-1 mice. These mice were 6-7 weeks old and were first irradiated with ultraviolet light twice a week for 20 weeks to ensure that they were high-risk for developing skin cancer. Two separate experiments were then conducted. In the first experiment on 60 mice, half (30 mice) had 100mg of a moisturising cream ‘Dermabase’ massaged gently into the skin daily, five days a week for 17 weeks. The other half were left undisturbed.
In the second experiment, 210 similar high-risk mice were divided into groups of about 30 and had one of five creams or one of three control treatments applied in the same way as the first experiment. The creams applied were Dermabase, Dermovan, Eucerin Original Moisturizing Cream, Vanicream, or a custom blend of creams. The ‘custom blend’ of creams has had a patent application filed on behalf of Rutgers, The State University of New Jersey and the pharmaceutical company, Johnson and Johnson. The control groups had either water massaged into the skin (30 mice) or were left untreated (27 mice) as in the first experiment. The researchers included a water control group in this second experiment, as they wanted to control for the stress caused to the mice by removing them from their cages, and applying and massaging in the creams. In the second experiment, they then combined both the control groups into a larger combined control group of 57 mice.
The number of tumours was counted and the size (estimated volume) of any tumour found was measured in both experiments. All tumours were then examined under the microscope to characterise them histologically, at the end of the study.
What were the results of the study?
Topical applications of 100mg of four of the creams (Dermabase, Dermovan, Eucerin Original Moisturizing Cream, or Vanicream) applied once a day, five days a week for 17 weeks to these high-risk mice significantly increased the number of tumours and the rate of increase in tumour size. The average increase in the total number of histologically defined tumours in the treated groups (Dermabase, Dermovan, Eucerin Original Moisturizing Cream, or Vanicream) compared to the untreated controls was 69%, 95%, 24% and 58%, for the four creams.
Topical applications of a specially designed Custom Blend cream to high-risk mice did not increase the proportion of mice with tumours, the number of tumours per mouse, or the tumour volume per mouse when compared with the water-treated control group.
What interpretations did the researchers draw from these results?
The researchers claim that their results indicate that several commercially available moisturising creams increase the speed at which tumours form and the eventual number of tumours when applied topically to high-risk mice, pre-treated with UV light. They go on to suggest that further studies are needed to determine the effects of topical applications of moisturising creams on sunlight-induced skin cancer in humans.
What does the NHS Knowledge Service make of this study?
This animal study appears to present valid results and to have been reliably conducted. The researchers believe that skin tumours that develop in animal models such as these mice, resemble sunlight-induced skin cancer that can develop in humans who receive heavy exposure to sunlight early in life and go on to develop skin cancer later in life in the absence of heavy sunlight exposure.
To extrapolate these findings to humans, it would be necessary to assume that the mice in this study were sufficiently similar to healthy humans applying normal amounts of moisturiser. However, humans and mice developed for laboratory experiments are very different, and additionally, the mice were heavily exposed to ultraviolet light throughout their early life to ensure that they were at a high-risk for developing skin cancer.
How well the skin of such high-risk albino mice resembles healthy human skin is questioned by the researchers, the commentators and most of the newspapers reporting this study and is critical in the interpretation of the relevance of the findings.
The Custom Blend cream, patented to the university and pharmaceutical company Johnson and Johnson, appeared best in the comparison. The publication reports its ingredients as; purified water, propylene glycol, stearyl alcohol, cetyl alcohol, polysorbate 20, isopropyl myristate, C12-15 alkyl benzoate, benzoic acid, glycerin, and sodium hydroxide. More human research on this and other moisturisers will certainly be required.
Whichever way the relevance of this animal study is interpreted, for now it seems wise not to read too much into the results, to continue using moisturiser as usual and to wait for reliable research in humans.
Sir Muir Gray adds...
Mouse traps are bad for mice but not for humans. No need to change my moisturising routine on this evidence.