"Morning C and evening A" is a popular phrase on the Internet, which refers to the use of skin care products containing vitamin C (including prototype VC and VC derivatives) in the morning and vitamin A (including alcohol A, aldehyde A and ester A) in the evening. This concept of skin care originates from photoaging theory, that is, ultraviolet rays will damage the skin during the day and weaken at night, so it is best to use skin care products with repair function. At the same time, vitamin C and vitamin A have the functions of whitening and brightening skin, anti-aging and promoting collagen synthesis in skin care products, so this skin care concept can not only whiten and brighten skin, but also make skin younger and in better condition.