Acnegenicity testing in rabbits. An objective quantification method.

An objective method for the quantification of follicular hyperkeratosis is proposed for the rabbit ear assay of acnegenicity. The area (area%) of hyperkeratinized follicles, covering a stereomicroscopic photo of the epidermis, is proposed for the quantification of the response. The uniformity of two observers' quantification was evaluated in six tested formulations. The quantification of the response in area% was found to be a suitable and objective alternative to visual scoring on a graded scale. The median relative difference between two observers' area%-quantification was found to be 26%, and there was no statistically significant difference between the two observers' quantification (p greater than 0.10). An area% of 2, 7, and 15 is preliminarily suggested to be equivalent to the lower limit for scores 1, 2 and 3 respectively.