Niacinamide
Vitamin B3 topical. Reduces redness, oil, pigmentation. Pairs with almost everything.
4-10% niacinamide reduces erythema, sebum, hyperpigmentation, fine lines. One of the safest, best-tolerated actives. Combines well with tretinoin, vitamin C, AHAs. Available OTC (The Ordinary, Paula's Choice) and in compounded prescription skincare.