Liquiritin reduces oxidative stress via promoting the expression of antioxidants and suppressing the expression of oxidants in the skin tissue samples. (A) mRNA levels of SOD1, SOD2, CAT and Nrf2 in the skin tissue specimens were calculated using reverse transcription-quantitative polymerase chain reaction analysis. (B) Western blot assays were performed to examine protein levels of XO, iNOS, NOX-2 and NOX-4 in the skin tissue samples of mice treated under various conditions. (C) Expression levels of NOX-2 were measured using immunohistochemical analysis in the skin tissue sections from mice. The red arrows refer to NOX2-positive cells. Scale bar, 100 μm. Data are presented as the mean ± standard error of the mean (n=10). ***P<0.001, compared with the Con group. +P<0.05, ++P<0.01 and +++P<0.001, compared with the UVB-only group. UVB, ultraviolet B; Con, control; SOD, superoxide dismutase; CAT, catalase; Nrf2, nuclear factor erythroid 2-related factor 2; XO, xanthine oxidase; iNOS, inducible nitric oxide synthase; NOX, nitric oxide.