¹Department of Pharmaceutical Toxicology, Faculty of Pharmacy, Istanbul University, Istanbul, Turkey DOI : 10.29228/jrp.133 Eugenol is a phenolic compound isolated from clove essential oil. It is used in dentistry, fragrance, cosmetic, and food industries. According to the fragrance ingredient safety assessment report, eugenol does not cause phototoxic reactions and genotoxicity. However, its effect on UV-induced cytotoxicity and genotoxicity has not been well examined. Here in this study, cytotoxic and genotoxic effects of eugenol are investigated on UVA-induced damage using human keratinocyte cells (HaCaT). HaCaT cells were treated with increasing concentrations of eugenol (10-500 μM) for 1 hour and irradiated with 5-10-15 J/cm2 UVA. 24 hours later the neutral red uptake (NRU) assay was used to evaluate cytotoxicity. For genotoxicity assay cells were exposed to 1-10 μM eugenol for one hour and non-cytotoxic UVA irradiation doses (1, 2.5 J/cm2) were used. The alkaline comet assay was carried out immediately after the UVA irradiation to measure the genotoxic potential of eugenol. The cytotoxicity assay results indicate that eugenol caused a cytotoxic effect in a dose-dependent manner in HaCaT cells and increasing doses of UVA-irradiation enhanced the cytotoxic effect of eugenol. The alkaline comet assay results showed that eugenol causes DNA single-strand breaks and increasing doses of UVA-irradiation aggravates the genotoxic potential of eugenol. These data demonstrate that eugenol has cytotoxic and genotoxic potential and eugenol aggravates UVA-induced cytotoxic and genotoxic response in HaCaT human keratinocytes. Keywords : Eugenol; UVA; DNA damage; human keratinocyte; cytotoxicity; genotoxicity