It's certainly not less effective with higher concentrations. Some dermatologists say that 5% niacinamide has the same results as 10% but it's less irritating. On the other hand, some claim that 10% niacinamide is better for acne, inflammation and redness.
Niacinamide is usually well tolerated even in higher concentrations. So if your skin isn't sensitive, there shouldn't be any issues even with a 10% niacinamide serum. If you want to go lower, some brightening serums have ~4% niacinamide, some toners too, but it's usually not in the name of the product, so you have to search by ingredients.
It's certainly not less effective with higher concentrations. Some dermatologists say that 5% niacinamide has the same results as 10% but it's less irritating. On the other hand, some claim that 10% niacinamide is better for acne, inflammation and redness.
Niacinamide is usually well tolerated even in higher concentrations. So if your skin isn't sensitive, there shouldn't be any issues even with a 10% niacinamide serum. If you want to go lower, some brightening serums have ~4% niacinamide, some toners too, but it's usually not in the name of the product, so you have to search by ingredients.