This method is designed to evaluate changes in DNA 8-oxoguanine content and/or cholesterol content in human skin tissue equivalents after exposure to ozone. For this study, the tissues will be treated topically overnight with either test materials, Trolox (positive control), or left untreated (negative control) and on the following day the tissues will be exposed to ozone (approximate dose of 10 PPM for one hour).  If 8-oxogunine is the desired endpoint then following the ozone exposure the DNA will be extracted from the tissues and subjected to enzymatic hydrolysis to reduce it to free nucleotides.  The free nucleotides will then be assayed for 8-oxoguanine content via a competitive ELISA based assay. If cholesterol is the desired endpoint, then lipids will be extracted from the tissues and then resolved on a TLC plate.  Cholesterol and any cholesterol diols will be visualized by spraying the TLC plate with 50% H₂SO₄.