Kojic Acid
A compound produced by certain fungi during fermentation, used in brightening formulas for the appearance of dark spots and a more even tone. It works on the same tyrosinase pathway as several other brighteners, which is why it is rarely sold alone and is usually blended with niacinamide, tranexamic acid or alpha arbutin for a broader effect. It oxidises and browns readily in air and light, so packaging and freshness matter, and a browning serum is a visible sign that potency is fading.
Studied for
- ·The appearance of an even tone
- ·The look of reduced dark spots and post-blemish marks
- ·The appearance of a brighter-looking complexion when paired with other brighteners
How it’s thought to work
Studied for the appearance of less visible uneven pigment through tyrosinase-related pathways, the same enzyme system targeted by arbutin and prescription hydroquinone; most supporting work uses it as one part of a brightening blend rather than on its own. Because it degrades with air and light exposure, its practical performance depends as much on formulation stability as on the percentage on the label.
In an 80 person trial, a kojic acid based formula supported more even looking skin tone, performing similarly to hydroquinone 4% cream.
Evaluation of a kojic acid, emblica extract, and glycolic acid formulation compared with hydroquinone 4% for skin lightening. Cutis, 2010.
View on PubMed (PMID 21049734) ↗Questions
- Why does my kojic acid serum turn brown?
- Kojic acid oxidises in air and light, and a browning formula is that reaction showing. It does not necessarily mean the product is unsafe, but potency drops as it darkens, so opaque packaging and using it fresh matter.
- Is kojic acid safe to use long-term?
- It has a long history of cosmetic use, though it can be sensitizing for some people at higher percentages or with prolonged exposure, so many formulas keep it low, around 1 to 2%, and pair it with soothing or barrier-supporting ingredients.
- What should kojic acid be paired with?
- It is commonly formulated alongside niacinamide, tranexamic acid or alpha arbutin, each working on a slightly different part of the pigment pathway, which is thought to give a broader effect than kojic acid alone.