Kojic Acid

What kojic acid is

Kojic acid, chemically 5-hydroxy-2-hydroxymethyl-4-pyrone, CAS 501-30-4, is a small organic molecule produced by certain fungi, most famously Aspergillus oryzae, the mold used for koji in sake and soy sauce production. Workers in Japanese breweries were said to have noticeably soft, even-looking hands, a story that brought the molecule into skin care. On this page kojic acid is sold as small crystals by the gram. Our product record lists it as easily soluble in water, ethanol and ethyl acetate and hardly soluble in diethyl ether.

Properties

In cosmetics kojic acid is valued for products aimed at a brighter, more even-looking complexion and at the look of dark spots. It is water-soluble, so it dissolves into toners, serums and the water phase of creams. Its weak point is color stability: light, oxygen, higher pH and iron traces can turn it yellow or brown over time. Good formulation practice, described below, keeps the product looking fresh.

Applications

Typical products are brightening serums, spot-focused gels, day creams for an even-looking tone, hand creams for the look of age spots, body lotions and wash-off masks. Kojic acid works well with Niacinamide, which targets a similar visual goal from another angle. If you need an oil-soluble, more color-stable form, choose Kojic Dipalmitate. Find more tone-focused ingredients in our cosmetic actives catalog.

How to use it

Dissolve the crystals in the water phase at room temperature or with gentle warming, then continue with the batch. Add a chelator such as sodium phytate or disodium EDTA and an antioxidant such as sodium metabisulfite or a vitamin C derivative compatible with your pH. Keep the finished pH mildly acidic, around 4.0 to 5.5, which helps color stability. For use levels, follow the CoA and your market's regulations; the EU SCCS has assessed kojic acid as safe up to 1 percent in face and hand products.

Keeping color stable

Discoloration is the most common complaint about kojic acid products. Use stainless steel or glass tools, never iron or copper. Keep air incorporation low, fill into opaque or airless packaging and store bulk cool and dark. Run stability with a light cabinet or a sunny windowsill sample next to a dark control. A slight yellow tint can be masked with a pale tint in the product, but prevention is better.

Compatibility

Kojic acid is compatible with niacinamide, glycerin, hyaluronic acid, panthenol, alpha arbutin and most nonionic thickeners. It does not like high pH, metal ions or strong oxidizers. Some preservatives that require neutral pH may not suit it, so pick one that works in mildly acidic products.

Characteristics

Form: small crystals, sold as a powder by weight. Chemical name: 5-hydroxy-2-hydroxymethyl-4-pyrone. CAS: 501-30-4. Solubility per our record: easily soluble in water, ethanol, ethyl acetate; hardly soluble in diethyl ether.

Original recipe: even-tone gel serum, 100 g

Phase A: distilled water 88.00 g, glycerin 3.00 g, sodium phytate 0.10 g, Kojic Acid 1.00 g. Stir until the crystals dissolve. Phase B: niacinamide 4.00 g, panthenol 1.00 g. Phase C: hydroxyethylcellulose 0.80 g predispersed in propanediol 1.10 g; stir into the batch until clear. Phase D: preservative suited to acidic pH 1.00 g. Adjust the pH to about 5.0 with citric acid or sodium hydroxide solution and fill into an opaque airless pump.

Record the lot number in your batch log so every production run can be traced back to its certificate of analysis. Retain a small sample of each lot for at least the shelf life of the finished product, since it makes later quality questions much easier to answer.

Storage

Keep the crystals sealed in a cool, dry, dark place. Close the container right after weighing to limit air and moisture. Ships from Florida in gram packs.