Niacinamide vs vitamin C: how each reads on a label

Two vitamins, two listed jobs

Niacinamide, also called nicotinamide, is a form of vitamin B3. The US Cosmetic Ingredient Review (CIR) describes it working in cosmetics mainly as a hair and skin conditioning agent.¹ The EU's CosIng database gives it a single function, smoothing², which CosIng defines as seeking an even skin surface by decreasing roughness or irregularities.³

Ascorbic Acid is vitamin C itself. CIR describes it and its salts as functioning primarily as antioxidants, with ascorbic acid also used to adjust pH.⁴ CosIng lists it as an antioxidant, buffering, fragrance and skin conditioning ingredient.⁵ Its definition of an antioxidant is written around the product: inhibiting reactions promoted by oxygen, thus avoiding oxidation and rancidity.³

Function names describe what an ingredient is used for in a formula. They are not promises about results, and CosIng states that its information has no legal value.⁶

Vitamin C goes by many names

A front label that says "vitamin C" can mean any of several ingredients, each with its own name and its own CosIng entry. Niacinamide has no such family on a label: it is listed as Niacinamide. The ingredient list is where you find out which vitamin C a product uses.

These are separate ingredients with separate reviews. CIR assessed ascorbic acid together with its calcium, magnesium and sodium salts and with magnesium and sodium ascorbyl phosphate, judging the data on one applicable to all of them; Ascorbyl Palmitate and the other ascorbyl esters had been reviewed earlier.⁴ Sodium Ascorbyl Phosphate and Ascorbyl Glucoside each have their own entry here too.

The same review notes that ascorbic acid is readily and reversibly oxidised to dehydroascorbic acid. Because certain metal ions can turn its antioxidant action into a pro-oxidant one, the panel cautioned formulators to make sure these ingredients are acting as antioxidants in a formula.⁴ That depends on how the product is made, which no list describes.

What the reviews recorded about amounts

When CIR reviewed niacinamide, reported use ranged from 0.0001% in night preparations to 3% in body and hand products.¹ For ascorbic acid, more than three quarters of reported uses were hair dyes and colours, at 0.3% to 0.6%; its other uses were either very low, under 0.01%, or 5% to 10%. Sodium ascorbyl phosphate was used at 0.01% to 3%.⁴ Both reviews date from 2005, so products on sale today may differ.

None of these figures appears on a pack. In the EU, ingredients above 1% are listed in descending order of weight and those below 1% may follow in any order¹³, so two serums that list Niacinamide in the same place can contain quite different amounts. A percentage printed on the front of a bottle is the brand's own statement. What position on a list tells you covers the rest.

The "don't combine them" advice

You may have read that niacinamide and vitamin C should not be used together. How the two behave side by side is an old question in chemistry: a pharmaceutical paper studied the interaction of nicotinamide with ascorbic acid in solution in 1963.¹⁴

More recent laboratory work measured something specific. In water under a UV lamp, ascorbic acid broke down about twice as fast with nicotinamide present, across the pH range tested, 2 to 12; the authors suggest nicotinamide accepts electrons from it.¹⁵ In oil-in-water creams exposed to UV, nicotinamide likewise acted as a photosensitiser for the breakdown of ascorbic acid, while vitamin E (alpha-tocopherol) had a stabilising effect.¹⁶

Those studies are about how a formula holds up under UV light in a laboratory. They did not test the pair on skin, and they did not test the vitamin C derivatives in the table above. They do show that pH and the other ingredients present change how fast ascorbic acid breaks down under light¹⁵¹⁶, and an ingredient list shows neither the pH nor how the formula is protected from light. Seeing both names on one list tells you that the formulator chose to combine them, not how well that formula keeps.

On the label

• Niacinamide is listed under that name; nicotinamide is the same substance. Niacin, or nicotinic acid, is a related but different ingredient.¹
• Vitamin C may be any name in the table above. Ascorbic Acid is the vitamin itself; the others are derivatives with their own names and entries.⁵
• A product can list more than one vitamin C form, and each name counts as its own ingredient.
• Position says little once you reach the part of the list below 1%, where any order is allowed.¹³
• Compare two serums with the ingredient list comparison tool, or paste one list into the skincare ingredient checker to see what each name is listed for.

Neither name is a verdict on a product, and a list cannot tell you how a formula behaves. For the rest of a label, see how to read a cosmetic ingredient list.