Kojic Acid: Notifying a Brightening Active Within the Rules

Kojic acid shows up in more brightening serums and soaps than almost any other active, and it also causes more filing confusion than most, mainly because it sits right at the edge of two problems: it's genuinely tricky to formulate stably, and the claim language around it needs care.

If you're notifying a kojic acid product for the first time, here's what actually matters.

The basics: INCI and CAS

Kojic acid's INCI name is simply Kojic Acid, which makes it one of the easier actives to identify correctly on a filing, no supplier trade name games to untangle. Its CAS number is 501-30-4. You'll sometimes also see kojic dipalmitate used as a more stable derivative, which has its own separate INCI name and CAS number and should never be confused with or substituted for plain kojic acid on a filing, since they are chemically distinct substances with different properties.

Item	Detail
INCI name	Kojic Acid
CAS number	501-30-4
Typical function	Skin brightening / antioxidant
Common derivative	Kojic Dipalmitate (separate INCI and CAS)
Typical use level	Varies by formula and market; check current concentration guidance for your target market

Always confirm current permitted concentration and any restrictions for your specific market before finalizing a formula. Restricted-ingredient lists get updated, and a level that was fine two years ago isn't guaranteed to still be fine.

Why it's a formulator's headache

Kojic acid is notoriously unstable. It oxidizes readily when exposed to air, light, and heat, and that oxidation often shows up visually as the product turning brown over its shelf life, sometimes within weeks in a poorly stabilized formula. This isn't just a cosmetic problem for the product's appearance, it also means the actual concentration of active kojic acid in the jar can degrade over time, so what you measured at batch release may not reflect what's in the product six months later.

A few things formulators do to manage this:

• Pair it with antioxidants like ascorbic acid derivatives or tocopherol to slow oxidation
• Use opaque or amber packaging to limit light exposure
• Keep pH in the stable range recommended for the specific formulation
• Consider the dipalmitate derivative, which is generally more stable, though it behaves differently in the skin and isn't a straight swap

None of this is filing advice exactly, but if your formula browns quickly during stability testing, that's a sign your kojic acid concentration at time of sale may not match what you intended to declare, which matters for accurate labeling.

The claim language line

This is where kojic acid gets people in trouble. "Brightening" and "evens skin tone" are standard cosmetic claims. But kojic acid is popularly known as a skin-lightening or de-pigmenting agent, and it's easy to slide into language that implies treatment of a medical pigmentation condition.

Safer cosmetic-side language:

• "Brightens the look of skin"
• "Helps even the appearance of skin tone"
• "Supports a more radiant complexion"

Riskier, drug-adjacent language:

• "Treats hyperpigmentation"
• "Fades melasma"
• "Clears dark spots" (depending on market, this can be read as treating a skin condition rather than describing a cosmetic effect)

The general rule that applies across active ingredients holds here too: describing a cosmetic effect on appearance is different from claiming to treat a named skin condition. Kojic acid products walk this line constantly because the ingredient's actual mechanism, inhibiting melanin production, sounds inherently medical even when the marketing stays cosmetic.

Filing it correctly

When you're filing, list Kojic Acid by its INCI name with your actual concentration or concentration range, the same as any other ingredient. If you're using a supplier blend that contains kojic acid alongside other brightening agents like alpha arbutin or niacinamide, remember to carry through the real math: the blend's declared kojic acid percentage times your use level of the blend, not the blend's internal percentage reported as if it were the finished product's concentration.

Double check it against your market's current prohibited and restricted substance list before finalizing, since kojic acid's regulatory status and permitted levels are exactly the kind of detail that shifts between reviews and varies by market.

Getting a brightening formula from bench to filed notification usually means juggling the active's own quirks, the supplier documentation for whatever blend you're using, and the claim language on your label all at once. Cosmetic Comply handles the ingredient-to-INCI matching and the restricted-list screening part of that, so you can spend your attention on the stability testing and the label copy instead.