In a previous article, I had suggested that the original source of the many claims along the lines of “skin absorbs 60% of everything we put on it”, and similar, may have been a paper by Pedersen et al, International Journal of Cosmetic Science, 2007, vol. 29, no5, pp. 361-367, and I debunked the claimed relevance of this study in that article, so I do not intend to repeat this here.
I now have been given further information by a contributor to PCT that suggests there may be another source of this internet rumour:
A footnote in the book “No More Dirty Looks” (O’Connor & Spunt) provide this:
The authors of the book state “, our dermis does let in lots of other things we put on it-as much as 60 percent, by some accounts.” pg 4
The full reference for this paper is ”The role of skin absorption as a route of exposure for volatile organic compounds (VOCs) in drinking water.” H S Brown, D R Bishop, and C A Rowan, Am J Public Health. 1984 May; 74(5): 479–484
From the abstract of this paper:
Assessments of drinking water safety rely on the assumption that ingestion represents the principal route of exposure. A review of the experimental literature revealed that skin penetration rates for solvents are remarkably high, and that the stratum corneum is a less effective barrier to penetration than traditionally assumed. Based on published skin absorption rates, we used Fick’s law (Jos = Kop delta Cos) to determine permeability constants for selected compounds. We then calculated dose per kilogram for nine different exposure situations and compared this to the oral dose per kilogram. We found that skin absorption contributed from 29-91 per cent of the total dose, averaging 64 per cent. Dose per kilogram body weight ranged from .0002 mg/kg-.18 mg/kg, with an average of .03 mg/kg. In weak aqueous solutions, flux of the solute is directly proportional to concentration. Laboratory approaches differ markedly from environmental exposures and can underestimate absorption. We conclude that skin absorption of contaminants in drinking water has been underestimated and that ingestion may not constitute the sole or even primary route of exposure.
The authors of No More Dirty Looks, (Siobhan O’Connor and Alexandra Spunt), have clearly taken the opportunity to cite a paper on skin absorption that demonstrates relatively high levels of absorption for the substances tested in the study. The absorption levels are quite high, and may seem quite shocking, but both the abstract of the study and the extract from the book are unspecific – i.e. there is no direct reference to the actual test substances by the authors and the study findings are extrapolated across the whole range of cosmetic ingredients without further qualification by the authors of the book.
So the question must be asked – what substances are being absorbed at such high levels by the skin, and under what conditions? (There is a clue in the title of the paper – “volatile organic compounds (VOCs) in drinking water”)
These are solvents that may be found at extremely low concentrations in drinking water – the focus of the study. None of these solvents (and please note that they are SOLVENTS) are used in skin care cosmetics. Toluene is only used in some nail products, with an extremely low risk of skin penetration.
About the authors of No More Dirty Looks Taken directly from their web site):
Siobhan is now Senior Editor at Prevention magazine in New York, the leading health magazine for women with more than 10 million monthly readers. As a magazine editor for the past ten years in New York, she has edited award-winning features for GOOD magazine and others, writes regularly for many national magazines, and recently won a Folio Award for feature writing.
Alexandra is a freelance journalist and marketing consultant in Los Angeles. She previously headed up the branding team at American Apparel where she helped develop the advertising campaign and was a company spokesperson. Before that she worked as a modeling agent for NEXT and, while in college, as a television host.
I do not intend making a personal attack on these ladies, but it is clear to me that neither of them has a scientific background (sadly typical of the authors of the type of book that seeks to paint the cosmetics industry as a cavalier destroyer of consumer health), yet they are taking scientific papers and using them as evidence to prove a case. And they do this entirely out of context due, presumably, to their lack of scientific expertise! A paper that shows the skin absorption of 3 substances (a statistically insignificant number) that are NOT used in cosmetics should NOT be used as any kind of evidence of skin absorption across the entire range of over 17,000 cosmetic ingredients. Whilst their actual statement is suitably vague, they have massively over-extrapolated the information available (“our dermis does let in lots of other things we put on it” – from data on THREE highly atypical substances!). Skin absorption is dependent upon so many factors, both in the nature of the substance involved and in the nature of the skin of any individual that it is not possible to make such generalised statements with any degree of meaning. Any statement on skin absorption should be confined to a specific substance, or a group of substances (if the properties are sufficiently similar to permit a general observation).
From the Brown et al study:
Absorption rates vary among individuals, and even for the same individual over time. Variables such as age, sex, ratio of body fat, previous exposure, nutrition, type and amount of skin exposed as well as the specific conditions of exposure will all affect actual absorption. Rates obtained from healthy adults will again tend to underestimate absorption for younger or more sensitive populations.
Physical and Chemical Properties of the Compound-
Factors affecting absorption include lipophilicity, polarity, volatility, molecular weight, carbon number, and solubility in the stratum corneum.
It is not my intention to suggest that O’Connor and Spunt have a written a book full of misinformation (I would need to read the book in order to make that judgment!), but with this statement on skin absorption they have certainly contributed to either initiating, or propagating yet another internet myth about cosmetics.
It seems a shame that the only people who feel moved to write populist books about the cosmetics industry are precisely those who should not do so. In order to correctly present information, it is vital to have the knowledge and ability to understand and interpret scientific studies. Reading a scientific paper is not the same as fully understanding it. This is another classic example of writers with a belief system being blinded by science and preventing their readers from finding any clarification of the reality of cosmetics. I am not suggesting that no-one is entitled to an opinion, but these opinions should not be presented as facts – in my opinion.
The fact remains, as summarised in the previous article on this subject, that there is NO basis for the general claim that ALL (or even many) cosmetic ingredients are absorbed by the skin without further qualification. Like many (most?) extreme claims (using ALL or NONE), it is not correct, and the truth lies somewhere in between the extremes. Clearly, SOME ingredients are absorbed to different extents, varying between very low and very high, and some are not absorbed at all. However, in some ways, the extent of skin absorption is irrelevant. If the substance is absorbed, metabolised and excreted without causing any measurable adverse effect, then there is no cause for concern.