- Aqueous gel preparations containing oleic acid/sodium oleate combinations were applied three times daily to hairless mice (CD1 strain). Six groups of animals ( n =9 or n =10) were treated topically with six experimental vehicles containing 2, 3 and 4.5% oleic acid (OA) at two different pH values, 7.3 and 7.7. Sodium lauryl sulfate (5%) in a similar gel preparation was used as the positive control ( n =5), while untreated animals were used as the negative control ( n =6). After three treatment days, the skin samples were collected and processed for histological evaluation. It was seen that the severity and frequency of histological changes in the skin treated with OA-containing vehicles were directly correlated with increased pH/ ionization (i.e. decreased OA/sodium oleate ratio) and with overall OA concentration.