Retinol Serum.

"If you're an absolute beginner, you won't use pure retinol. You'll start with a retinol base like Plum. You can start by applying it two times a week, then three times a week, then four times a week, then five times, and so on. You can use it daily eventually. But if you're using pure retinol at 0.3, 0.5, or 0.6 concentration, whether you're a beginner or a pro user, don't apply it more than three to four times a week because that will irritate your skin. For first-time users, use it a few times a week, like two to three times a week actually two times a week is okay. Space it out so if you apply it on Monday, apply it next on Friday. Then after two weeks, use it three times. Then after four weeks, make it four times, and that becomes your daily use. Always use a small amount of retinol and cover it up with a moisturizer."