The physiological metabolic cycle of the skin is 28 days. Generally, the skin will be automatically updated once every 28 days. Gradually, the metabolism of young people is faster, while that of the elderly is slower. I think if you have been exposed to the sun for a long time, you will turn white immediately before long. It will take some time, probably after a winter protection period (that is, March-April). Individuals should pay attention to sun protection and insist on using whitening mask for a period of time, which will improve.