You can't use the brightening cosmetic ingredient niacinamide and vitamin C together?

Representative brightening cosmetic ingredients include niacinamide and vitamin C. However, there are cases in which niacinamide and vitamin C should not be used together. It is said that when niacinamide and vitamin C are used together, there may be conflicts between ingredients and harmful ingredients may be produced. Can't niacinamide really be used with vitamin C? We will be a man who reads cosmetics, who strives to create a safe cosmetics use culture.
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