Retinol is the ultimate age fighter. But everything from its concentration (usually somewhere between .25% and 1% when it’s over the counter) to its co-stars—hyaluronic acid, vitamin F, vitamin B₃—are what make certain products best for some complexions, others better for others. One thing is for sure: If you’re a retinol newbie, start slow (e.g. applying only at night), then work up to more frequent use. Retinol is effective because it’s strong, which means your skin could get irritated. What’s waiting on the other side of that irritation is the skin of your dreams, so go gradually and get ready for greatness.