Olive (Olea europaea L.) leaves have long been used in folk medicine and herbal tea in Europe and the Mediterranean area. The Mediterranean climate is characterized by high temperatures, and by strong ultraviolet B (UVB) radiation causing the skin to age, increasing wrinkling, pigmentation and skin thickness. The aim of this study was to examine the effects of an olive leaf extract and its component oleuropein on skin damage caused by acute UVB irradiation in C57BL/6J mice. The extract (300 or 1000 mg/kg) and oleuropein (25 or 85 mg/kg) were administered orally twice daily for 14 days. UVB was administered daily at a dose of 120 mJ/cm(2) for the first 5 days and then every other day for 9 days. Both treatments inhibited the increases in skin thickness induced by radiation. They also inhibited increases in the Ki-67- and 8-hydroxy-2'-deoxyguanosine-positive cell numbers, melanin granule area and matrix metalloproteinase-13 (MMP-13) expression. These preventive effects on UVB-induced skin damage might be caused in part by inhibiting the degradation of extracellular matrixes in the corium, and by the proliferation of epidermal cells through the inhibition of increases in MMP-13 levels and reactive oxygen species induced by irradiation.