We cover a wide range of water-soluble and oil-soluble actives including niacinamide (vitamin B3), ascorbic acid and vitamin C derivatives, hyaluronic acid and sodium hyaluronate, AHAs (glycolic acid, lactic acid, mandelic acid), BHAs (salicylic acid), retinol and retinoids, peptides, azelaic acid, tranexamic acid, kojic acid, resveratrol, coenzyme Q10, bakuchiol, and more. For each active, our guides cover the evidence base for its skin benefits, the correct usage percentage range, the pH range at which it's effective, compatibility with other actives and ingredients, potential irritation considerations, and how to incorporate it into different product formats — serums, creams, toners, and treatments. We also explore active stacking — which combinations work synergistically and which should be kept in separate products or used at different times of day to avoid irritation or efficacy loss. Whether you're tackling hyperpigmentation, building an anti-ageing routine, formulating for acne-prone skin, or simply want to understand what the actives in your current products are actually doing, this category gives you the ingredient science you need.