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J. Soc. Cosmet. Chem., 36, 425-433 (November/December 1985) A quantitative in vitro assay for the evaluation of phototoxic potential of topically applied materials. II. Modification and assessment of low level activity* JOSEPH C. D•NARDO, BARBARA A. WOLF, WILLIAM E. MORRIS, SAUL TENENBAUM, and RICHARD W. SCHNETZINGER, Revlon Research Center, Inc., 2121 Route 27, Edison, NJ 08818. Received November 7, 1984. Synopsis There are numerous reports in the scientific literature which describe photobiological effects of materials in cell and animal models. In an effort to develop a quick and inexpensive phototoxicity screen as well as to reduce the number of animals required to predict product safety, a quantitative in vitro assay using Saccha- romyces cerevisiae was developed and reported previously by the present authors. Activity of test materials in the assay was measured by zones of growth inhibition around the perimeter of a treated disc and compared to a concentration curve based on activity of 8-methoxy psoralen, a known phototoxic agent. The present study reports on a modification of the original method undertaken to reduce the time necessary to complete the assay without affecting the quantitative ability to assess a response. Additionally, "low level" in vitro phototoxic activity for a number of complex fragrance oil materials was compared to test results from an animal model, and the ability of benzophenones and sunscreen agents to inhibit a phototoxic response is also reported. In vitro results from the modified assay compared to published animal and human data for a number of fragrance raw materials showed good agreement between the methods. The in vitro assay devel- oped has shown to be useful as a prescreening tool for evaluating phototoxic potential of fragrance ingre- dients as well as an effective means of reducing the number of animals required for experimentation prior to assessing consumer safety. INTRODUCTION The use of a microorganism to observe a photobiologic effect has been reported as early as 1908 by Reitz (1). Since that time, a number of studies have been published refining various techniques and procedures which evaluate these effects for a variety of agents. Currently, there has been a heightened interest by the scientific community in utilizing such in vitro systems in an attempt to reduce the number of animals required for sub- stantiating product safety. As part of a continuing research effort to comply with such interest, a number of studies were initiated to develop and validate a quantitative in vitro assay for the evaluation of phototoxic potential of topically applied materials. The second in a series of research papers on alternatives to animal toxicity studies. 425