Hello! I am getting a niacinamide serum formulated and I want 10% niacinamide in it while manufacturer says "We don't suggest to add niacinamide to 10% because what we use for raw material is pure and high-concentrated, it need to dilute before adding into serum. So 5% is the most."
How true is that?
Moreover, what's best alternative to zinc PCA 1%?