It comes from fermentation, specifically from fungi used for centuries in Japan to process rice and make saké, and in cosmetics it is one of the few brightening actives with a long, well-documented history of use. On the label, it appears as Kojic Acid, or in its esterified form, Kojic Dipalmitate.
Kojic acid acts on the same enzyme as hydroquinone, but through a different mechanism: it removes copper from tyrosinase’s active site. It’s an elegant mechanism with two practical implications: a legally mandated maximum concentration and a stability issue that determines product quality.
Article by Elisa Avalle, founder of LeLang Skin Care and dermocosmetics specialist. Cover image created with the help of artificial intelligence.
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How it works
Tyrosinase is a copper-dependent enzyme: without that ion in its active site, it cannot function. Kojic acid chelates it, meaning it binds to it and makes it unavailable, slowing melanin production.
It doesn’t destroy pigment that is already present. It acts on the pigment that would be produced from now on, which is why results appear over weeks, not days: you have to wait for the stratum corneum to renew and carry away the old pigment. The pace of this turnover is explained in the article on cell turnover.
The concentration, and why it can’t be higher
The European safety assessment set the maximum for cosmetic use at 1% in face and hand products. This isn’t a symbolic limit: above certain concentrations, kojic acid can cause sensitization, and contact dermatitis is the most frequently reported adverse effect in the literature.
So, a cream claiming very high concentrations of kojic acid either doesn’t actually contain them or isn’t compliant. It’s one of the few checks you can do in two seconds by looking at the packaging.
The oxidation problem
It’s a molecule that’s unstable in light, air, and changing pH: it oxidizes and darkens. If a product turns dark yellow or amber after a few weeks, that means the active is degrading, and a degraded active can’t do what it was put there to do.
That leads to two formulation choices worth recognizing. The first is Kojic Dipalmitate, the ester with palmitic acid: much more stable, oil-soluble, and released more gradually. The second is the packaging: airless or an opaque tube, never a transparent jar that’s opened every day.
What it pairs with
On its own, it’s rarely enough, and that’s not a weakness specific to this molecule: in skincare for discoloration, combination is the strategy, because there are several points in the chain that leads to pigment that can be targeted.
- With niacinamide, which works further along the process by hindering the transfer of pigment to surface cells.
- With vitamin C, which adds antioxidant activity and also interferes with tyrosinase.
- With alpha hydroxy acids, which speed up the removal of already pigmented corneocytes and improve the penetration of other actives.
When to use it
In fall and winter. This isn’t just an aesthetic convention: treating dark spots takes weeks, and doing so when UV exposure is at its peak means replenishing every day the pigment you’re trying to reduce.
Daily sun protection isn’t an accessory to the treatment; it’s half the treatment, and should be continued afterward, too. The role your skin phototype plays in all this is explained separately.
Cosmetics do not treat clinical conditions and cannot claim to do so, under Regulation (EC) 1223/2009 and Regulation (EU) 655/2013. Melasma and any spot that changes shape, color, or size should be assessed by a doctor.
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Frequently asked questions
What is kojic acid?
Kojic acid is a molecule produced through fermentation, particularly by fungi used for centuries in Japan to process rice and make saké. In cosmetics, it’s one of the few brightening actives with a long, documented history of use. On labels, it appears as Kojic Acid or, in its esterified and more stable form, as Kojic Dipalmitate.
How does kojic acid work on dark spots?
It acts on tyrosinase, the enzyme that initiates melanin production and needs a copper ion to function. Kojic acid binds to this copper and makes it unavailable, slowing pigment synthesis. It doesn’t act on pigment that is already present, but on what would form later. That’s why results become noticeable over several weeks, as the stratum corneum renews.
What is the maximum concentration of kojic acid in cosmetics?
The European safety assessment set the limit at 1% in face and hand products. Above certain concentrations, kojic acid can cause sensitization, and contact dermatitis is the most frequently reported adverse effect in the literature. Products claiming much higher concentrations therefore warrant caution: it’s a simple check you can do by reading the packaging.
Why does a kojic acid cream change color?
Because the molecule is sensitive to light, air, and changes in pH: it tends to darken as it oxidizes. If a product turns dark yellow or amber after a few weeks, that indicates the active is degrading. That’s why carefully formulated products often use Kojic Dipalmitate, which is more stable, and airless packaging or opaque tubes instead of transparent jars.
What does kojic acid pair well with?
With actives that work on other points in the chain leading to pigment: niacinamide, which hinders melanin transfer to surface cells; vitamin C, which adds antioxidant action; and alpha hydroxy acids, which promote renewal of the stratum corneum. Fall and winter are the ideal seasons to use it, always with daily sun protection throughout the treatment and afterward.
Sources for this article
- European Scientific Committee on Consumer Safety (SCCS), opinion on kojic acid in cosmetic products.
- Rivas S., Pandya A.G. (2013). "Treatment of melasma with topical agents, peels and lasers: an evidence-based review". American Journal of Clinical Dermatology, vol. 14, no. 5, pp. 359-376.
- Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products.
- Commission Regulation (EU) No 655/2013, laying down common criteria for the justification of claims used in relation to cosmetic products.
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