Retinol is an active ingredient of "vitamin A" family. It is a proven anti-aging, antioxidant, skin-restoring, firming ingredient. It speeds up cell turnover of the skin. It works at the cellular level of the skin and promotes collagen production. It has anti-acne benefits and also prevents clogging of pores. However, retinol is photosensitive, so always use broad-spectrum sunscreen when you are using retinol-based products. Since it is an active ingredient, it may cause purging, redness, skin inflammation, and dryness.
Ideally, one must consult his derm before starting using retinol.