Yes, it is considered safe to use Vitamin C and Niacinamide together in the same product or applied at the same time as a part of your skin care routine.
How do these ingredients work?
As we age our skin becomes thinner and more susceptible to redness and inflammation. Niacinamide, also known as vitamin B3, works as an anti inflammatory to reduce redness and irritation in the skin.
Why do some caution against using them together?
There is an old study from almost 60 years ago that showed that when these two products were used together under unique circumstances involving extremely high temperatures led to the development of nicotinic acid that is irritating to the skin. This will not happen in real world circumstances.
Can these two ingredients work together?
There are some studies that show that using these two ingredients together can improve dyspigmentation.