Optimum conditions for Radix Rehmanniae polysaccharides by RSM and its antioxidant and immunity activity in UVB mice

► Optimization of Radix Rehmanniae polysaccharides was done using response surface methodology (RSM). ► Optimum extraction conditions were: extraction temperature 100 °C, extraction time 2 h and ratio of liquid to solid 6. ► The model had a satisfactory coefficient of R2 (=0.9815) and was verified experimentally. ► Radix Rehmanniae polysaccharides protect against skin oxidative stress in experimental mice.