Niacinamide

Niacinamide at 4–5% has demonstrated anti-aging and wrinkle-smoothing effects by boosting collagen and key structural protein production. At 2–5%, it significantly lightens hyperpigmentation by suppressing melanosome transfer, and at 2% it increases ceramide, free fatty acid, and cholesterol synthesis to strengthen the skin barrier and improve hydration. It also exhibits sebum-regulating and anti-inflammatory properties that benefit acne, rosacea, and atopic dermatitis.

No specific contraindications are noted in the source. The source does mention it can be combined with tyrosinase inhibitors (e.g., vitamin C, arbutin, kojic acid) for enhanced brightening effects, and that anti-aging benefits require consistent use at 4–5% for 8–12 weeks.