Kojic acid is a common skin-brightening and spot-fading ingredient. It primarily works by inhibiting tyrosinase activity to reduce melanin production, thereby improving dark spots, acne scars, and dull skin tone. It itself is not highly photosensitive and theoretically can be used during the day. However, because the skin becomes more sensitive to UV rays after using kojic acid, if strict sun protection is not taken during the day, it will not only affect the whitening effect but may also worsen pigmentation. Therefore, it is recommended to use it at night and apply sunscreen during the day.