Citric Acid as a pH Adjuster: INCI, CAS, and Use Levels

Citric acid is the ingredient that shows up in almost every water-containing formula at a tiny percentage and then gets almost no attention on the ingredient list, which is a shame because it's doing real work and it's genuinely simple to document correctly once you know what box it fits in.

What it is and why it's there

Citric acid is a naturally occurring organic acid, the same one that gives citrus fruit its tartness, produced commercially by fermentation rather than squeezed from lemons. In cosmetics it shows up doing one of two jobs, sometimes both at once in the same formula.

The first job is pH adjustment. Many cosmetic bases, especially surfactant systems and emulsions, land at a pH that's higher than what's ideal for skin feel, preservative efficacy, or stability, and a small addition of citric acid brings that number down. The second job is chelation. Citric acid binds trace metal ions, like iron or copper, that can otherwise catalyze rancidity in oils or destabilize certain preservative systems. A formula might use it for one reason, the other, or both.

The identifiers

Field	Value
INCI name	Citric Acid
CAS number	77-92-9
Typical function	pH adjuster, chelating agent
Typical use level	Fractions of a percent up to around 1 percent, occasionally higher in exfoliating or peel-type products
Restriction status	Not on Canada's Cosmetic Ingredient Hotlist as a prohibited or specifically restricted substance in this general use

That CAS number, 77-92-9, is worth writing down once and keeping in your ingredient reference file, because it's the identifier that follows the substance regardless of which supplier or trade name you're buying it under. Trade names never appear on a regulatory filing. Everything gets mapped back to INCI and, where relevant, CAS.

Where the confusion starts

The trouble with citric acid isn't the ingredient itself, it's how makers record it when it arrives as part of something else. Citric acid rarely shows up as a standalone raw material in a small workshop. More often it's baked into a preservative blend, a buffer system, or a pre-made surfactant base as one of several components.

That matters because supplier blends need to be expanded into their individual components on your ingredient list and on a notification filing. If your preservative blend is added at 1 percent of the finished product and the blend's own documentation shows it's 5 percent citric acid, then citric acid's real concentration in your finished product is 0.05 percent, not 1 percent and not zero. Skipping that multiplication step is one of the more common ways an ingredient list ends up technically wrong even though every raw material was disclosed by the supplier in good faith.

A worked example

Say you're making a facial toner with the following at the raw material level:

• Aqua, to 100 percent
• A surfactant/humectant blend at 3 percent, which itself contains 2 percent citric acid as a pH stabilizer
• A preservative system at 0.8 percent, unrelated to citric acid

The citric acid contribution from that blend works out to 3 percent multiplied by 2 percent, which is 0.06 percent in the finished toner. That's the number that belongs in your records and, where a range or specific concentration is requested, on your notification. Writing "citric acid, trace" without doing this arithmetic is technically incomplete even if it's common practice among smaller brands.

Practical habits worth adopting

• Ask every supplier for the full INCI breakdown of any blend, not just the trade name and a percentage of "active."
• Keep a standing conversion sheet for blends you use repeatedly, so you're not re-deriving the math every batch.
• Record citric acid's contribution even when it's small. Small percentages still need to be accurately represented, particularly since pH adjusters are exactly the kind of ingredient that gets glossed over as "inactive."
• If your formula changes, for instance you switch preservative suppliers and the new blend carries a different citric acid load, that's a formula change that may call for an amendment to an existing notification, not just an internal note.

If tracing every blend back to its individual INCI components sounds like the kind of bookkeeping that eats an afternoon, that's the exact gap Cosmetic Comply is built to close. It takes your ingredient list, including the supplier blends, expands them into their real components with INCI names and CAS numbers, carries the percentages through the math, and flags anything that needs a closer look before it goes anywhere near a filing.