Glycolic Acid + Kojic Acid
Use With Caution
These ingredients can be combined, but require careful timing, lower concentrations, or gradual introduction.
Kojic acid and glycolic acid are effective together for hyperpigmentation but can cause significant irritation and sensitization, especially on darker skin.
What the Research Says
Kojic acid is a chelation agent produced by certain fungi (Aspergillus and Penicillium species) during the fermentation of rice. It inhibits tyrosinase by chelating the copper ions essential for the enzyme's function, effectively reducing melanin production. As a depigmenting agent, it is widely used in concentrations of 1-4% for melasma, post-inflammatory hyperpigmentation, and general skin brightening. The logic of combining it with glycolic acid is sound: glycolic acid accelerates turnover of pigmented cells from the surface while kojic acid slows new pigment production at the melanocyte level.
However, both ingredients carry meaningful irritation potential that becomes additive when combined. Kojic acid is a known contact sensitizer - it can cause allergic contact dermatitis, redness, stinging, and paradoxical darkening in sensitized individuals. Glycolic acid's barrier disruption can increase the skin's permeability to kojic acid, amplifying both its efficacy and its irritation potential. For darker skin tones (Fitzpatrick types IV-VI), this heightened irritation risk is especially concerning because inflammatory responses in melanin-rich skin frequently trigger post-inflammatory hyperpigmentation - potentially worsening the very condition the combination is meant to treat.
Dermatologists who combine these ingredients typically do so in controlled formulations with precise concentrations and buffer systems, often in professional peel settings rather than daily-use products. At-home combination requires careful introduction, low concentrations, and vigilant monitoring for signs of irritation or sensitization.
Timing & How to Use
Do not layer kojic acid and glycolic acid in the same routine. Use glycolic acid in the evening and kojic acid in the morning, or alternate days. Start with low concentrations of both (1-2% kojic acid, 5% glycolic acid) and increase gradually over 4-6 weeks. Discontinue immediately if persistent redness or stinging develops.
Practical Tips
- 1Patch test kojic acid on the inner forearm for 48 hours before using it on the face alongside glycolic acid
- 2Kojic acid is unstable and oxidizes easily - discard products that have turned brown or dark yellow
- 3Kojic dipalmitate is a more stable derivative with less irritation potential, though slightly less potent
- 4If you have darker skin prone to PIH, use this combination only under dermatological guidance
References
- Saeedi M, et al. Kojic acid applications in cosmetic and pharmaceutical preparations. Biomed Pharmacother. 2019;110:582-593.
- Lajis AFB, et al. A review of techniques of the production of kojic acid from microbial sources. Molecules. 2020;25(12):2918.
- Burnett CL, et al. Final report of the safety assessment of kojic acid as used in cosmetics. Int J Toxicol. 2010;29(6 Suppl):244S-273S.
