You’ll want to start slow with retinol. Initially, applying it once a week at night is your best bet. And you’ll want to follow it with a moisturizer, because it can be drying. Once your skin is used to retinol, you can progressively use it more often. But keep in mind that for many people, a nightly application would be too drying for their skin no matter how long they’d been using it for, so that shouldn’t necessarily be your goal.