What niacinamide concentration should I use in a private label serum?

The most clinically studied and consumer-accepted range is 5% to 10% niacinamide. At 5% you get well-documented benefits for uneven skin tone and barrier support with minimal risk of irritation. At 10% efficacy increases but so does the potential for flushing if nicotinic acid impurity levels in the raw material are not tightly controlled. Always ask your cosmetic chemist for a Certificate of Analysis confirming nicotinic acid content below 0.5%.