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What determines skin sensitization potency-myths, maybes and realities. Part 1. The 500 molecular weight cut-off

PainSci » bibliography » Roberts et al 2013
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One page on PainSci cites Roberts 2013: Does Epsom Salt Work?

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND: It is widely accepted that there is a molecular weight (MW) cut-off of 500, such that single chemicals with MWs higher than 500 cannot be skin sensitizers. If true, this could serve as a useful principle for designing non-sensitizing chemicals.

OBJECTIVES: To assess whether the 500 MW cut-off is a myth or a reality.

METHODS: A database of 699 chemicals tested for skin sensitization in guinea pigs or mice was analysed to establish the number of tested chemicals with MW> 500, and to establish whether any of these were sensitizers.

RESULTS: Only 13 (2%) of the 699 chemicals in the database have MW> 500. Of the 13 tested compounds with MW> 500 in the database, five are sensitizers and eight are non-sensitizers.

CONCLUSIONS: The 500 MW cut-off for skin sensitization is a myth, probably derived from the widespread misconception that ability to efficiently penetrate the stratum corneum is a key determinant of sensitization potency. The scarcity of sensitizers with MW> 500 simply reflects the general scarcity of chemicals with MW> 500.

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