1777
Assay conditions chosen mimic the distinct human epidermal reactivity compartments of the skin surface ( pH 5 . 5 ) , stratum basale ( pH 6 . 8 ) , and typical physiological conditions ( pH 7 . 4 ) .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None