Some say these two should not be used together because if mixed and used on our skin, they offer no benefits to the skin.
I have listed these arguments towards the end of this section and explained why these arguments are not valid.
Theoretically, niacinamide and vitamin C can be used together.
Having said that, if you want to be cautious, it is safer not to use them together.
The main reason to avoid using them together is that skincare is expensive (especially a good vitamin C product), so why take the risk?
Why not use one in the morning and the other in the night? Why not use them on alternative mornings? Why not use them on alternative nights? There are plenty of options – you don’t have to stop using either of these – try not to use them together.
But if you are really keen to use them together in the same routine, then below are a few pointers:
Why should NOT be used together & Are these arguments valid?
1960s study
According to a 1960s study, when niacinamide products are mixed with vitamin C products, these two negate each other’s benefits. The skin receives no benefit. Pure vitamin C (l-ascorbic acid) was used in the study.
The problems with focussing on this study
The ingredients used in this study were not stable. Skincare formulation science has progressed a fair bit since the 1960s. These days, manufacturers use the stable version of niacinamide and vitamin C.
This study does not apply to vitamin C. Many skincare manufacturers use vitamin C derivatives.
pH issue
Vitamin C skincare products work well on the skin with an acidic pH (below 4). pH measures the acidity or alkalinity of a solution.
Niacinamide skincare products work well on the skin when they have a neutral pH (pH around 5).
One argument people have is that if we were to mix these two, the pH of both products would be messed up, so it wouldn’t work well on our skin.
The problem with this argument
This argument would be valid if we mix these two in our palms and apply the mixture to our skin. But if we apply one product first, wait for 3 to 4 minutes, and then apply the second one, this argument becomes invalid.
Nicotinic acid and redness on skin
Another argument is that when these two are applied together, nicotinic acid is formed on the skin. Skin reacts badly to nicotinic acid and will become inflamed and red.
The problem with this argument
Yes, indeed, the skin reacts badly to nicotinic acid. However, nicotinic acid only forms when these two are mixed together at very high temperatures. These high temperatures are not found in a typical home setting—we are talking of temperatures above 120 degrees Celsius / above 248 degrees Fahrenheit.