Influence of shaving on study results in sensitization tests using guinea pigs

Although many alternative methods for evaluating the sensitization potential of compounds have been investigated in recent years, the guinea pig test method generally continues to be used. It is not difficult to imagine that the technique of shaving with a shaver, which is done in guinea pig evaluations, physically removes the stratum corneum of the epidermis. In this study, we examined the effect of the hair trimming technique on skin reactions. The test method followed the Adjuvant and Patch test method: the back skin of 7-week-old female guinea pigs was treated with 25% Hexyl cinnamic aldehyde (HCA)/acetone as a sensitizing substance according to the usual method. Thirteen days after the start of secondary sensitization, the dorsal abdominal skin was dehaired, and 1% HCA/acetone solution was applied as an inducing treatment. The left side of each animal's trunk was shallowly shaved and the right side was deeply shaved to evaluate the differences in skin reactions. Skin reactions were evaluated 24 and 48 hr after induction. For histological examination, untreated animals were shaved as in the treated group, and skin samples were taken at 0, 24, and 48 hr after shaving for histological evaluation. The results showed that animals tested negative in shallowly shaved sites but positive in deeply shaved sites, and most animals had enhanced skin reactions. Additionally, histopathological examination revealed a decrease in the amount of stratum corneum remaining in the deeply shaved sites. These results indicated that the degree of hair shaving may have a significant effect on sensitization assessment.