Retinol is a vitamin A derivative that boosts collagen and speeds up cell renewal. If you want to include it in your skincare routine, dermatologist Gagan Raina says, "Begin in your mid-20s with 0.1-0.3% concentration, apply a pea-sized amount at night on dry skin, and follow with moisturiser and sunscreen." "Retinol is not a miracle; it's a method," she adds.