For example, to reduce skin inflammation and brighten the complexion, combining these two vitamins during your skincare routine is ideal. Biologically, they act differently to limit the appearance of brown spots: vitamin C inhibits tyrosinase, an enzyme necessary for melanin production, while niacinamide (a water-soluble derivative of vitamin B3) blocks the transfer of pigments into cells. Niacinamide will also stimulate the synthesis of lipids and restore the skin's barrier function. It thus decreases the transepidermal water loss and maintains the skin hydrated longer, preventing the appearance of fine dehydration lines.
Concerning the application, there is no preferential order to apply these two active ingredients on your skin. Choose the care product with the most fluid texture first. A serum is generally applied before a cream with a higher viscosity. Vitamin C and niacinamide are not photosensitizing ingredients, so these vitamins can be applied to the skin in the morning or evening. However, remember to use a broad-spectrum sunscreen to protect yourself from the harmful effects of UV radiation during the day.
BISSETT L. & al. A Review of the range of effects of niacinamide in human skin. IFSCC Magazine (2002).
TELANG P. S. Vitamin C in dermatology. Indian Dermatology Online Journal (2013).