Sometimes flushing and mild burning but for that can usually be avoided by working your way up to 5% and regular continued use. Naicinamide serum at 5% is expensive though, a lot of folks make their own...you can Google for recipes. I would try a product with it first to see how your skin responds. I don't know your skin type but if it's on the oily side Olay Regenerist Regenerating Serum has a good amount of it. If your skin can handle a bit of moisture Cerave PM moisturizer is a good option as well.