Ascorbic acid is notoriously unstable in the presence of water, it quickly oxidizes into dehydroascorbic acid which is yellow/orange in colour and (according to current research) isn’t as effective as ascorbic acid in producing skin benefits like evening of skin tone, reducing free radicals and reactive oxygen species, and increasing collagen production.
There are many compounds made from ascorbic acid that are designed to keep the antioxidant more stable. However many of these compounds haven’t been shown to act the same way as ascorbic acid or penetrate the skin. As well, enzymes in the skin are required to convert these compounds back into ascorbic acid, and there is little evidence to show that this occurs to a large extent.
By removing water from the formula, ascorbic acid can be stabilized against oxidation and experiments have shown that it can be so stable that it can resist months of exposure to oxygen (the test formulas were bubbled through with oxygen, like a fish tank!).
By removing water, we often create heavier, stickier, and much shinier products. This prototype, while heavy feeling on the finger, applied with a relatively matte and light finish. Hopefully it will stand up to stability testing, but I was so excited that I had to try it on myself immediately!
Niacinamide and ascorbic acid on their own are great skin care ingredients. Ascorbic acid is not only a good water-soluble antioxidant, but may also increase production of collagen in the skin which can help mitigate some of the damaging effects caused by UV exposure.
Niacinamide is a good anti-inflammatory which makes it useful for treating inflammatory conditions like acne and has been shown to increase naturally occurring moisturizers in the skin.
They’re both very effective at reducing hyperpigmentation of the skin – it’s easy to see why people would want to use the two of them together.
If you Google Niacinamide and Vitamin C, you’ll get some posts about not combining them. The worry is that they form a 1:1 complex and cancel out each other’s skin benefits.
There are two main chemical reactions that occur when you mix niacinamide and ascorbic acid. The first occurs when you mix niacinamide with any acid (or base), and that’s the conversion of niacinamide to niacin. This takes a long time and is more of a concern for manufacturers that are using niacinamide in acidic products.
The second concern is the formation of a complex between niacinamide and ascorbic acid. I think the worry is that this complex is no longer effective in benefiting the skin, and I’ve also seen concerns that it may produce hydrogen peroxide which can lead to skin cell death.
I took a look at the research to get a better understanding of these two chemical reactions. It is important to note that a few of these papers are old, so they don’t use newer visualization techniques that can help us quantify chemical changes and structures more accurately.
Hydrolysis of Niacinamide to Niacin
Amides, like niacinamide, are very stable compounds. This stability means it takes a lot of heat and concentrated acids or bases to get niacinamide to turn into niacin (also known as nicotinic acid).
I’m going to do a separate post that will explain this more, but the important thing to see is that the -NH2 group, a nitrogen and two hydrogens, is replaced with an -OH group, an oxygen and a hydrogen.
Heat vastly speeds up reactions; a rough approximation is that every 10 °C (18 °F) increase in temperature doubles the reaction rate. If the pH 2 solution was kept at 30 °C (86 °F) we could expect it to take over 4800 hours or almost half a year – and that’s if the acidic solution didn’t corrode your skin first!
An experiment with temperature conditions closer to room temperature shows how heat affects the rate of conversion. Only after 6 weeks of storage at 45 °C (113 °F) in acidic pHs did they find niacin, and the conversion never exceeded 2%. At room temperature (25 °C or 77 °F) the amount of niacin was less than 1% after 6 weeks, but the measurement wasn’t accurate enough to tell exactly how much, just that a small amount was present.
Another thing to keep in mind is that reaction rates also slow down when the viscosity or thickness of the solution is increased. Most skin care products, even serums, are thickened to some extent – which will further slow down the conversion of niacinamide to niacin.
If we can get metaphorical for a second, chemical reactions aren’t like a distance race. They’re more like jumping over hurdles. There’s a minimum amount of energy that’s needed to cause the molecule to change, called the activation energy. If you don’t have the energy to jump over a hurdle, you can’t progress. You can’t just roll on the ground until you hit the finish line.
It’s also important to note the difference between irritation due to an acidic product versus the flushing caused by niacin. Niacin flushing appears evenly, affecting everywhere it’s been applied. It is also temporary (often lasting longer than 20 minutes), and comes with a tingling sensation.
If you’re using a product with niacinamide and ascorbic acid in the ingredients list and aren’t noticing any skin reddening…there’s either very little niacin that’s been formed, or you’re not very sensitive. If you’re worried about a product that contains both ingredients, storing it in a cool environment will discourage transformation of niacinamide to niacin.
But what about applying a product with niacinamide and then one with ascorbic acid? Is niacin being formed? I don’t want to say absolutely not, but the amount potentially formed is so miniscule, I don’t think it’s a relevant worry.
Niacinamide and Vitamin C (Ascorbic Acid) Complex
Mixing niacinamide and ascorbic acid turns the two clear solutions a yellow colour, but this isn’t the same yellow colour that appears when ascorbic acid is oxidized into dehydroascorbic acid.
This experiment also found that the pH of the solution that the two are mixed together in affects how much of the niacinamide ascorbate is formed. Niacinamide ascorbate forms best at a pH close to 3.8, but at pHs higher or lower less is formed. This means if the pH of a solution they were mixed together in was changed, away from 3.8, the two molecules would separate from each other.
This means if we added the same number of molecules of niacinamide and ascorbic acid into a solution of pH 3.8, about half of them would be in the niacinamide ascorbate complex, and the rest of them would just be on their own floating around.
I’m going to do a separate post that will walk through the calculation of this.
The pH dependent formation is important, because only the surface of our skin is acidic. Each deeper layer of skin becomes less and less acidic, finally reaching physiological pH which is around 7. This means as the niacinamide ascorbate moves deeper into the skin, there’s less impetus for them to be associated with each other. As well, as more individual ascorbic acid and niacinamide molecules move into the skin, the ratio of free to complexed niacinamide and ascorbic acid would decrease, and the complexed niacinamide ascorbate would separate until equilibrium was reached again.
So the important takeaway is to know that the yellow colour isn’t the same thing as an oxidation of ascorbic acid, and that the complex formed between niacinamide and ascorbic acid is completely reversible. The niacinamide and ascorbic acid are held together like two pieces of paper with static, versus glue.
Many skin care ingredients will degrade or change with UV exposure, but using a sunscreen will greatly reduce or even eliminate the chances of this occurring.
The paper also theorized that by mixing the niacinamide and ascorbic acid with tocopherol (Vitamin E), the radical production could be mitigated.
I hope this has helped you understand what’s occurring when you mix niacinamide and ascorbic acid (or any acid) together. While there are chemical reactions that occur, they either occur super slowly, or are reversible.
You can definitely still choose to use niacinamide and ascorbic acid separately. You could use ascorbic acid during the day and niacinamide in the evenings. If you do choose to use them together, I don’t think the evidence points to any disabling of their benefits or any skin damage.
People do often experience some redness or tingling when using the two, but I think that can be chalked up to the irritation caused by ascorbic acid, especially if the product isn’t pH adjusted and acidic. I don’t want to suggest you to take a niacin pill to experience a flush, but unless the redness is very even and demarcated, it’s not likely due
Edit: Nicotinic, not nicotonic – apologies for the typo!