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On skin permeability, according to Wikipedia:

"Human skin has a low permeability; that is, most foreign substances are unable to penetrate and diffuse through the skin. Skin's outermost layer, the stratum corneum, is an effective barrier to most inorganic nanosized particles.[22][23]"

However there is little to be found on exactly what chemicals can permeate the unbroken skin.

This paper http://oem.bmj.com/content/61/4/376.full states the following:

"Many chemicals can cross the unbroken skin."

"However, the highly lipophilic nature of most solvents can also result in dermal uptake when deposited on the skin."

Is Wikipedia's statement incorrect? What chemicals can permeate the skin, which ones cannot, and why?

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  • $\begingroup$ Just a warning that this is a pretty broad question. Would you be satisfied with some examples rather than some overall theory? $\endgroup$ – user467 Jun 8 '14 at 21:26
  • $\begingroup$ Ideally a simplification of the overall theory, but examples would also be interesting. $\endgroup$ – AttributedTensorField Jun 8 '14 at 21:29
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"Skin's outermost layer, the stratum corneum, is an effective barrier to most inorganic nanosized particles."

But skin is quite permeable to many organic compounds. DMSO is one example, and it is warned that DMSO is a good solvent for other compounds that could be more toxic than DMSO.

Another example: we all (should) know that mercury is toxic. However, it's not going to hurt you much if you roll it around in your hand for a brief period (don't breathe in, though!). But organic mercury compounds are terribly toxic and skin permeable, including the infamous dimethyl mercury which killed a famous researcher of toxins.

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  • $\begingroup$ What are some examples of organic compounds that cannot permeate through the skin? $\endgroup$ – AttributedTensorField Jun 14 '14 at 5:20
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There are many phsico-chemical properties of the penetrant that determine the skin permeability of the substance. I cite this list from Kanerva, Lasse, ed. Handbook of occupational dermatology. Springer, 2000.

  • Polarity
  • Volatility
  • Solubility
  • Concentration
  • Molecular weight and particle size
  • Electrostatic charge

Of course it also depends on the site of application and how is the skin at the moment of the application however:

in general, non polar, lipid-soluble substances traverse skin more readily than do ionic species. Substances that penetrate skin easily include lipd-soluble endogenous substances (hormones, vitamins D and K) and a number of xeonobiotic compounds. Common examples of these are phenol. nicotine, and strychnine. Some military poisons, such as the nerve gas sarin permeate the skin very readily.

Manahan, Stanley E. Toxicological chemistry and biochemistry. CRC Press, 2002. p.121

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