Dermatologist's Take
Kojic acid is a mild tyrosinase blocker used to fade dark spots and melasma, usually at 1% to 2%. It is a reasonable option if hydroquinone is too harsh or you would rather not use it, but be clear on the trade-off: it is weaker, and the human evidence is thin because most trials tested it inside combination formulas rather than on its own. Use it once daily with sunscreen every morning and give it 8 to 12 weeks. If the product turns yellow or brown, the kojic acid has oxidised and stopped working, so buy it in opaque, air-tight packaging and replace it when the color shifts.
At a glance
- AKA 5-hydroxy-2-(hydroxymethyl)-4-pyrone
- 1-2% typical; capped at 1% in the EU and UK
- Works with niacinamide, vitamin C, azelaic acid
- Evidence: Moderate - small trials, mostly combination formulas
What is it?
Kojic acid is a compound made by fungi, mostly Aspergillus oryzae - the mold called koji that ferments rice and soybeans into sake, miso, and soy sauce. It was first identified in 1907 and is still produced by fermentation rather than pulled from a plant. In skincare it is used to fade dark spots, post-acne marks, and melasma. Most serums and creams contain 1% to 2%; some products sold outside Europe go higher, and it is also common in rinse-off soaps, where contact time is short and less of it gets into the skin.
How it works
Kojic acid blocks tyrosinase, the enzyme your pigment cells use to build melanin. It works by grabbing the copper atom that tyrosinase needs in order to function, so the enzyme slows down and less new pigment is made. Existing spots then fade gradually as the skin sheds and replaces itself.
That is the same target hydroquinone and arbutin aim at, and it is worth knowing why kojic acid still ends up weaker in practice. In a test tube, kojic acid actually grips the enzyme harder than hydroquinone does. But in living skin models hydroquinone clears pigment far more effectively, because it does more than block the enzyme - it is also toxic to pigment cells themselves. Lab potency and real-world results are not the same thing here, which is a useful caution whenever you see a chart ranking brightening ingredients.
Subtypes
- Kojic acid - the standard form. Water-soluble, well studied relative to its alternatives, and the one regulators have assessed. It is also the least stable.
- Kojic dipalmitate - kojic acid with two fatty acid tails attached. It resists browning, blends into oils more easily, and is often chosen by formulators for shelf life. The catch is that it has to be broken back down in the skin to do anything, and there is very little human data showing how well that happens. Treat a percentage of kojic dipalmitate as not directly comparable to the same percentage of plain kojic acid.
Concentrations
- 1% - the legal maximum in the EU and the UK for leave-on face and hand products, and the level both the EU's scientific committee and the US Cosmetic Ingredient Review panel concluded is safe. Effective, if slow.
- 2% - the most common strength worldwide and the concentration used in most of the published trials. Still sold in the US and much of Asia.
- Above 2% - found in some soaps and imported serums. There is no good evidence that higher percentages fade pigment faster, and irritation climbs. There is no reason to seek these out.
- In cleansers and soaps - washed off within a minute, so the dose reaching your skin is small. Fine as an add-on, not a substitute for a leave-on product.
Conditions it treats
What to expect
Expect fading over 8 to 12 weeks, not days, and only if you wear sunscreen daily - sun exposure makes new pigment faster than kojic acid can slow it down. Start once a day at night and move to twice daily only if your skin stays comfortable. Mild stinging or pinkness in the first couple of weeks is common; kojic acid irritates more readily than niacinamide or arbutin, so if you have sensitive or rosacea-prone skin, start every other night.