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j. Soc. Cosmet. (5hem., 47, 41-48 (January/February 1996) Petrolalum is not comedogenic in rabbits or humans: A critical reappraisal of the rabbit ear assay and the concept of "acne cosmetica" ALBERT M. KLIGMAN, Department of Dermatology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104. Accepted March 8, •996. Synopsis The objective was to find out whether petrolatum, previously reported to be comedogenic in the rabbit ear model, would worsen acne. Vaseline petrolatum jelly (Vaseline ©, Chesebrough-Ponds) and Vaseline pe- trolatum jelly cream (Creamy Vaseline ©, Chesebrough-Ponds) were applied to separate groups of ten acne patients each twice daily for eight weeks. No evidence of comedogenic potential was found by the follicular biopsy technique. Papulo-pustules significantly decreased in both groups. Greasiness cannot be equated with comedogenicity. The admonition for acne patients to seek "oil-free" skin care products has no scientific merit with regard to comedogenicity. Cosmetics are an unlikely cause of the relatively high prevalence of post-adolescent female acne. INTRODUCTION In a 1972 paper entitled "Acne cosmetica," Kligman and Mills reported that as many as 50% of commercial cosmetics were comedogenic in the rabbit ear model (1). Since then, this assay has been extensively used by producers of drugs and cosmetics to assess their potential for inducing acneform eruptions (2). Recently, manufacturers have added the human back test to appraise acnegenicity. Reputable manufacturers of cosmetics rou- tinely screen their products for comedogenicity in order to satisfy the consumer that their product is "non-comedogenic," a useful claim in a highly competitive market. However, neither the rabbit nor the human assay is entirely satisfactory. Serious con- troversies have sprung up regarding the reliability and relevance of the rabbit ear model. A voluminous literature reveals remarkably divergent results among laboratories and investigators. Substances deemed to be strongly comedogenic by some are declared by others to be innocuous. Reviewers have not failed to notice the high frequency of strikingly contradictory results. Long ago Frank questioned whether the rabbit ear model had any relevance for humans (3). The most extreme example of the controversies generated by the rabbit ear assay is the publications of Fulton, a prominent acneologist 41