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These days, while it’s (more) common knowledge that acidic compounds like hydroxy acids should not be used with retinol, the interaction between two other prominent and well-studied compounds: niacinamide and L-ascorbic acid, is rarely discussed. Ironically, along with hydroxy acids and retinoids, these two compounds to a great extent constitute and represent four of the five main classes of ingredients that should be included in everyone’s ideal skin care routine; the fifth class being sunscreen of course!
I’m surprised that this interaction hasn’t gotten more press! Therefore, let’s dive right in.
What Exactly Is This interaction?
L-ascorbic acid or vitamin C, requires a pH of less than 3.5 in order to penetrate the skin, which is very close to the 3.8 pH value where maximum complexation occurs between itself and niacinamide. L-ascorbic acid is the naturally-occurring form of vitamin C, while niacinamide is the –amide form of niacin or vitamin B3 as discussed in a previous post. When mixed together in aqueous solutions (since both are water-soluble vitamins), they form a 1:1 complex that turns the solution yellow, rendering both compounds useless. This complexation may be the result of a donor-acceptor interaction between L-ascorbic acid (donor) and niacinamide (acceptor), which may be similar to the interaction that occurs between tryptophan and niacinamide.
Furthermore, in the presence of UV light and oxygen, which seems likely since antioxidants (such L-ascorbic acid and niacinamide) are frequently and complementarily used with sunscreens to enhance UV protection (and since oxygen is everywhere), the two compounds may even generate the very reactive hydrogen peroxide compound through a 4-step chain reaction.
Now, the amount of complexation is pH dependent, with the maximum value occurring at a pH of 3.8. And since L-ascorbic acid requires a pH of 3.5 or lower in order to be protonated and absorbed into the skin, the likelihood of this interaction occurring and its consequent impacts are significant.
So don’t mix the two compounds!
Does This Occur with Vitamin C Derivatives?
In the presence of UV light, niacinamide and L-ascorbic acid can form hydrogen peroxide, a known pro-oxidative compound. Most if not all vitamin C derivatives such as ascorbyl tetraisopalmitate, magnesium ascorbyl phosphate, and ascorbyl glucoside, have to convert to L-ascorbic acid in order to have vitamin effects on the skin. This conversion process takes place after the derivates have penetrated into the skin. (Wouldn’t it be nice if they converted in the bottle?!) And because this conversion takes place within the skin, the pH of the surrounding solution or environment is no longer very low. However, the pH of skin is still acidic.
Therefore, interactions between any converted L-ascorbic acid and niacinamide are still possible. Keep in mind that the rates of conversion and penetration of the various derivatives can vary drastically, meaning that some may be more prone to complexation than others.
Fortunately, the pro-oxidative tendencies of hydrogen peroxide can be ignored in this scenario, since its formation is not possible in the absence of UV light.
So What Should I Do?
I think the more appropriate question is, “What should I NOT do?”
Clearly, it is my recommendation to NOT use niacinamide and L-ascorbic acid together since even in the absence of UV light, it would have an overall negative effect compared to when the two compounds are used separately. In the presence of UV light, the two compounds can form the pro-oxidative ROS-generator hydrogen peroxide, in addition to the 1:1 complex discussed above.
And while this interaction with niacinamide was only documented with L-ascorbic acid, it seems logical to suggest that it may also occur (albeit to much lesser extent) with vitamin C derivatives since they convert to L-ascorbic acid after penetrating into the skin. However, the amount of the 1:1 complex forming in these cases involving vitamin C derivatives is likely irrelevant.
Now, if you feel compelled and that you MUST use these two compounds together, try to use them at nighttime and/or wait 30 minutes between application to allow for the pH of the skin to return to its (more) natural state.
I hope this was a fun post and feel free to ask any questions down below or on my blog! And if you’ve been using both of these compounds together, don’t be afraid to share your (old) routine!