Tretinoin (all-trans retinoic acid) accelerates skin cell turnover, stimulates collagen, reduces hyperpigmentation, and treats acne. Sixty years of clinical data; the gold standard for topical anti-aging.
Dose: Pea-sized amount, 0.025-0.1% strength, at night, on dry skin.
Caveats: Irritation, peeling, and photosensitivity in the first 6-12 weeks. Build slowly. SPF mandatory. Not for pregnancy.