Aloe vera whole leaf extracts are incorporated into a wide variety of topically applied commercial products. Aloe vera whole leafextracts contain anthraquinones, which can generate reactive oxygen species (ROS) upon UVA light irradiation. In this study, thephototoxicity of two Aloe vera whole leaf extracts, Aloe A and Aloe B, were examined. The Aloe B extract was prepared by treatingthe Aloe A extract with activated carbon (1%, wt/wt) and filtration to remove the Aloe latex components, including the anthraquinones.UVB irradiation of the Aloe vera whole leaf extracts induced lipid peroxidation in the presence of a lipid, methyl linoleate. The amountsof lipid peroxides formed were higher in the Aloe B, which contained lower amounts of anthraquinones than Aloe A. Sodium azideinhibited and deuterium oxide enhanced the formation of lipid peroxides by Aloe B, suggesting that singlet oxygen was involved inthe mechanism. When superoxide dismutase was incorporated prior to irradiation, lipid peroxidation was inhibited, indicating thatsuperoxide was produced during the photoirradiation of Aloe B. In addition, electron spin resonance (ESR) spectroscopy was also usedto investigate the generation of free radicals by the UVB photoirradiated Aloe B. ESR measurements indicated that the UVB photoirradiationof Aloe B produced carbon-centered free radicals. These results suggested that, as with the exposure to UVA light, the exposureof Aloe vera whole leaf extracts to UVB light can also generate ROS and induce lipid peroxidation.