Same 5% Niacinamide, Different Serum: What pH and Vehicle Can Change

Niacinamide serums are sold on a percentage, 5%, 10%, even 20%, but the number on the bottle is only part of the story. A 2026 laboratory study suggests the pH of the formula can change how much niacinamide gets into skin, in some cases by about a factor of two. That finding is early and comes from lab models, yet it gives shoppers a more useful question than 'how high is the percentage?'

What the 2026 pH study measured

Researchers publishing in Scientific Reports in March 2026 tested 5 wt% niacinamide on full-thickness human skin from three female donors (ages 38 to 59) and on a lab-grown 3D epidermis, using diffusion cells held at skin temperature for 24 hours. They compared two solutions: one buffered at pH 5.0 and one at pH 7.4.

Neutral pH roughly doubled permeation. In human skin, flux was about 56 micrograms per square centimeter per hour at pH 7.4 versus about 22 at pH 5.0. In the reconstructed epidermis it was about 108 versus 68. Niacinamide solubility was nearly identical at both pH values (about 46 wt%), so the authors attribute the gap to the skin barrier itself rather than to how much niacinamide was available to push in.

Why pH might change the barrier

The authors propose that at neutral pH, free fatty acids in the outer skin layer become partly deprotonated, creating lipid defects that let more through. They measured electrical resistance of the membrane, which was roughly 2 to 4 times lower at pH 7.4, consistent with a more permeable barrier. They also report the effect was reversible when the pH was switched back and forth in 12-hour blocks.

That mechanism is inferred, not directly observed, and the authors list real limits: few replicates, large donor-to-donor variation, a switch experiment run on a single donor, and skin that had been frozen before use. Treat this as a hypothesis worth watching, not a rule for choosing a product.

Higher penetration is not the same as better results

Here is where it is easy to over-read the study. More niacinamide crossing the barrier in a diffusion cell does not show that skin looks better, and a barrier that is more permeable is not obviously something to aim for. The paper measured delivery, not visible outcomes.

Delivery is still a legitimate question, though. A 2024 review in Drug Delivery and Translational Research describes niacinamide as a widely used cosmetic ingredient and notes that understanding how it permeates skin matters for formulation design, including strategies for improving permeation. In other words, formulators already treat delivery as a design variable. The pH study adds one more variable to that list.

What the vehicle can do

A 2021 study in Pharmaceutics shows how much the carrier can matter. Six healthy volunteers had five different 5% niacinamide formulas applied to forearm sites, and researchers measured how much niacinamide reached the outer skin layer one hour later. Tape-stripping recovered 118.6 micrograms per square centimeter from a propylene glycol and oleic acid vehicle versus 39.3 from propylene glycol alone, a threefold gap at the same 5% strength.

The authors are careful about what that means: n = 6, one time point, one body site, and a result they describe as evidence of delivery rather than clinical efficacy. Two measurement methods also disagreed for one of the vehicles. Still, the message is consistent with the pH paper: two serums with the same percentage can behave differently on skin.

Why labels rarely help

Most consumer labels show the percentage and nothing else. pH is almost never printed, and the vehicle is hidden in an ingredient list sorted by amount. A 2026 randomized study of a niacinamide-containing regimen used after a laser procedure illustrates the gap: it reported improvements in barrier measures and wrinkle scores against a basic cream, but the niacinamide concentration was declared proprietary, and the serum also contained other actives, so the results cannot be credited to niacinamide alone. The study was funded by the manufacturer, and sponsor employees were among its authors.

None of this means a high percentage is a mistake. It means the percentage is one input among several, and a brand that discloses pH or publishes its own test data is giving you more to work with than one that only advertises a bigger number.

How to shop and use it with this in mind

• Look for disclosed pH or testing. Some brands list a pH range on their site. If none does, that is common, not a red flag by itself.
• Do not chase the highest percentage. The studies here used 5%, and none showed that a larger number gives a better-looking result.
• Note the rest of the formula. Humectants such as glycerin and supporting emollients can influence how a serum feels and how well skin tolerates it.
• Patch test a new serum. Apply a small amount to the jaw or inner arm for several days before using it on the full face.
• Introduce one change at a time. If you add a new serum and a new acid in the same week, you will not know which one is responsible for stinging or a flushed look.
• Moisturize and wear sunscreen as usual. A serum does not replace either step.

The takeaway

The best available lab data say pH and vehicle can shift how much niacinamide enters skin, even when the percentage is the same. The honest limit is that no one has shown that a higher-delivery serum looks better on a face. Use the percentage as a starting point, favor brands that tell you more about their formula, and judge a serum by how your skin looks and feels after a steady month or two, rather than by the number printed on the front.