Kojic Acid
Kojic Acid — evidence, uses & status

Class: small_molecule
Synonyms: KA
5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one
INCI: Kojic Acid
Function tags: skin appearance (cosmetic)
hyperpigmentation appearance
even tone / brightening
Overall evidence grade: C
WADA prohibited: no
Last updated: 2026-07-20

In brief: Kojic acid (KA) is a fungal fermentation product and a long-established tyrosinase inhibitor — it works by chelating the copper the enzyme needs. Its mechanism is strong (among the most consistent tyrosinase inhibitors in comparative lab work) and there is some standalone clinical signal: a 2013 RCT found 1% kojic acid alone reduced melasma severity. But the register grade is held at C because the caveats stack higher than for any other brightener here: most efficacy data comes from 2–4%, above the EU's 1% cap (Regulation 2024/996), so compliant products are milder than the studies; it is the brightener most associated with allergic contact dermatitis; it is chemically unstable and photosensitising; and it is almost always used in combination, so isolated evidence at a compliant strength is limited. A real ingredient with a real mechanism — honestly the most caveated of the pigment set.

## Identity

a compound produced by fungi during fermentation — its skin-brightening power was first noticed on the pale hands of sake brewers. It is a long-established, globally recognised depigmenting agent, and also chemically **unstable** (prone to oxidising and losing potency) and, in the EU, now **regulated**: Regulation 2024/996 — the same package that capped [retinol](/compound/retinol) at 0.3% — limits kojic acid to a maximum of **1%** in leave-on face and hand products. For the full readable explanation of what it is and how it works, see the companion guide, [what is kojic acid?](/learn/what-is-kojic-acid)

## Development & history

- Isolated in Japan in 1907 from *Aspergillus oryzae* (koji mould), the microorganism behind sake, miso, and soy sauce.
- Studied seriously for skin brightening from the 1980s–1990s and adopted globally as a depigmenting cosmetic active.
- Flagged by the EU in 2019 as a potential endocrine disruptor (over animal-study thyroid concerns); after SCCS review, concluded safe at 1% and capped there by Regulation 2024/996, with non-compliant products phased out through 2025.

## Mechanism (as proposed)

it **inhibits tyrosinase** by chelating the copper ion the enzyme needs to function — disarming the pigment machinery by removing a critical part rather than jamming the assembly line. In comparative laboratory work it is one of the **most consistent** tyrosinase inhibitors, reducing melanin without cytotoxicity in cell studies. The mechanistic case is genuinely strong; the gap, as always, is between a clean lab result and a real-world cosmetic outcome — widened here by the EU 1% cap (most studies used 2–4%), its instability, and its tendency to be used in combination rather than alone.

## Related reading

- The full readable guide: [what is kojic acid?](/learn/what-is-kojic-acid)
- Where kojic acid ranks among the pigment actives, in [best ingredients for dark spots and hyperpigmentation](/learn/best-ingredients-for-hyperpigmentation).
- Its frequent partner (different mechanism, complementary): [alpha arbutin](/compound/alpha-arbutin).
- The gentler brighteners it is usually combined with: [niacinamide](/compound/niacinamide), [vitamin C](/compound/vitamin-c), and [azelaic acid](/compound/azelaic-acid).
- Capped by the same EU regulation: [retinol](/compound/retinol). And the non-negotiable base for any pigment work: [how to use sunscreen](/learn/how-to-use-sunscreen).

Evidence grades by outcome:
outcome: Hyperpigmentation / melasma (appearance, usually in combination)
grade: C
base: Deo 2013 randomized study — 1% kojic acid alone reduced melasma severity, with the combination against hydroquinone stronger
effect: Gradual fading of melasma-related pigmentation
caveat: Most efficacy data comes from 2–4%, above the EU 1% cap; often used in combination
outcome: PIH (appearance, in combination serums)
grade: C
base: Combination-serum evidence (kojic acid paired with tranexamic acid and niacinamide)
effect: Softening of post-inflammatory marks within a combination
caveat: A combination result, not kojic acid alone
outcome: Tyrosinase inhibition (mechanism / in-vitro potency)
grade: B
base: Saeedi 2022 review — among the most consistent tyrosinase inhibitors in comparative in-vitro work, acting by chelating the enzyme's copper cofactor
effect: Strong, consistent enzyme inhibition in the lab
caveat: This grades the MECHANISM, not clinical proof; lab potency does not equal a cosmetic outcome
outcome: Standalone / EU-compliant-strength efficacy
grade: C
base: EU Regulation 2024/996 caps kojic acid at 1%; most efficacy studies used 2–4%
effect: Compliant products are milder than the studied strengths
caveat: Isolated standalone evidence at a 1% compliant strength is limited
outcome: "Whitening" overall skin-tone lightening
grade: D
base: Marketing claim
caveat: The human trials measured melasma severity and the fading of discrete spots and post-inflammatory marks — not a shift in baseline constitutive skin colour, which is what the whitening promise asserts. Evens the look of existing pigment; does not lighten the skin a person already has
outcome: Tolerability & stability
base: Nakagawa 1995 — kojic acid is the brightener most associated with allergic contact dermatitis; it is also chemically unstable and photosensitising
effect: Higher irritation and sensitisation risk than gentler brighteners
caveat: A caution, not a benefit. Patch test; well-packaged (opaque, air-tight) products matter because it oxidises

Legal status:
region: EU
status: Restricted — maximum 1% in leave-on face and hand products
note: EU Regulation 2024/996 (the same package that capped retinol at 0.3%) limits kojic acid to a maximum of 1% in leave-on face and hand products, after an SCCS review that concluded 1% is safe for consumers. Older non-compliant products were phased out. Much of kojic acid's strongest efficacy evidence comes from 2–4%, so an EU-compliant product is deliberately milder than what the studies tested.
region: INT
status: Lawful cosmetic ingredient
note: Kojic acid is a long-established, globally recognised cosmetic brightening ingredient. Concentration limits and rules vary by region; the EU cap of 1% is the notable restriction.

Cosmetic claims:
allowed: for the appearance of a brighter, more even complexion
helps reduce the look of dark spots
brightening support within a combination routine
forbidden: treats melasma
treats hyperpigmentation
cures dark spots
bleaches skin
inhibits tyrosinase
skin-whitening

Honest note: Kojic acid is a cosmetic ingredient, framed around the appearance of tone. In the EU, Regulation 2024/996 caps it at a maximum of 1% in leave-on face and hand products; most efficacy studies used 2–4%, so EU-compliant products are milder than what was tested. It is the brightener most associated with allergic contact dermatitis, and it is unstable and photosensitising — so patch testing, well-sealed opaque packaging, and daily sunscreen matter more here than with gentler brighteners. Persistent or hormonal pigmentation such as melasma is a dermatologist's territory, and pregnancy use is best discussed with a doctor.

Sources:
Deo KS, Dash KN, Sharma YK, Virmani NC, Oberai C. Kojic Acid vis-a-vis its Combinations with Hydroquinone and Betamethasone Valerate in Melasma: A Randomized, Single Blind, Comparative Study of Efficacy and Safety. Indian J Dermatol. 2013;58(4):281-285.
Desai S, Ayres E, Bak H, et al. Effect of a Tranexamic Acid, Kojic Acid, and Niacinamide Containing Serum on Facial Dyschromia: A Clinical Evaluation. J Drugs Dermatol. 2019;18(5):454-459.
Saeedi M, Eslamifar M, Khezri K, et al. Review on the Use of Kojic Acid — A Skin-Lightening Ingredient. Cosmetics. 2022;9(3):64.
Nakagawa M, Kawai K, Kawai K. Contact allergy to kojic acid in skin care products. Contact Dermatitis. 1995;32(1):9-13.