UVA radiation provokes the generation of reactive oxygen species (ROS), which induce oxidative stress in the exposed cells leading to extensive cellular damage and cell death either by apoptosis or necrosis. One approach to protecting human skin against the harmful effects of UV radiation is by using herbal compounds as photoprotectants. This study evaluated the protective effects of Prunella vulgaris L. (Labiatae) and its main phenolic acid component, rosmarinic acid (RA), against UVA-induced changes in a human keratinocyte cell line (HaCaT). Human keratinocytes exposed to UVA (10-30 J/cm(2)) were treated with an extract of P. vulgaris (1-75 mg/l) or RA (0.9-18 mg/l) for 4h. P. vulgaris and RA exhibited ability to reduce the UVA-caused decrease in a cell viability monitored by neutral red retention and by LDH release into medium. The P. vulgaris extract and RA significantly suppressed UVA-induced ROS production, which manifests as a decrease in intracellular lipid peroxidation, elevation of ATP and reduced glutathione. Post-treatment with P. vulgaris extract and RA also significantly reduced DNA damage. In addition, UVA-induced activation of caspase-3 was inhibited by treatment with P. vulgaris and RA. The P. vulgaris extract and RA demonstrated a concentration-dependent photoprotection (maximum at 25-50 mg/l and 9 mg/l, respectively). These results suggest that P. vulgaris and RA, used in skin care cosmetics, may offer protection against UVA-induced oxidative stress and may be beneficial as a supplement in photoprotective dermatological preparations.