I wouldn’t use both in the same formula. I know some people claim Niacinamide can be used in low pH formulations, but I still think it doesn’t worth it. Several reasons:
- Suggested pH for Niacinamide is around 6.0. That’s because Niacinamide has nicotinic acid as impurity and lower pH will boost burning sensation and irritation from it. There are some forms sold by. for example, makingcosmetics, where they claim it has much less of impurity comparing to normal niacinamide.
- Acids cause irritation. Niacinamide in big doses does it too. Combining both together increase irritation even more. But of course it depends on the percentage.
- Products, which usually combine niacinamide and big percentage of acids, have niacinamide at the end of the INCI list near preservatives, meaning it is just a claim ingredient and added in 1% or lower.