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Skin pH: practical implications regarding chemical allergens and toxics.

Occupational and Environmental Exposures of Skin to Chemicals, Stockholm, Sweden, June 12 -15, 2005. Morgantown, WV: National Institute for Occupational Safety and Health, 2005 Jun; :1
Both organic compounds and inorganic compounds and elements may exist in an ionized form that is pH dependent. It is well known that ionized organic compounds and non-ionized inorganic elements are appreciably less well absorbed through the skin than their corresponding non-ionized and ionized forms, respectively. Roughly, because pH is expressed on a logarithmic scale, for each 1 pH unit change, the ionization of compounds changes 10-fold. Thus, the pH of the skin environment in which these contaminants reside is important in respect to determining the amount of passage through the skin of ionizable chemicals that are potential allergens or systemic toxics. Unfortunately, there is no consensus on a scientifically defensible default assumption for the pH of human skin. Published literature have reported measured skin pH over the range 2.4 to 7+. A recent European Directive, 94/27/EC for the testing of nickel dissolution from worn jewelry items specifies using a simulated sweat pH of 6.5, but provides no documentation to support this choice of pH. It appears that this default pH was derived from a 1974 paper by Pedersen, et al. who likewise provided no justification for this choice, but was among one of the first researchers to create a simulant sweat. A survey of measured skin pH was undertaken among a variety of people in different environments in order to better identify a default skin pH among adults. From the preliminary data, it appears that a more representative skin pH lies between pH 4 and 5. If this assumption is accepted, it would mean that the potential amounts of dissolution of such elements as nickel using the EC method could underestimate the result by a factor of about 100-fold.
Skin-tests; Skin-irritants; Skin-exposure; Skin-absorption; Exposure-assessment; Risk-analysis; Organic-compounds; Inorganic-compounds; Ionization
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Occupational and Environmental Exposures of Skin to Chemicals, Stockholm, Sweden, June 12 -15, 2005