According to Dr. Leslie Baumann‘s Cosmetic Dermatology, kojic acid (5-hydroxy-2-(hydroxymethyl)-4-pyrone) is used in skin care formulations to lighten the skin, like another agent, hydroquinone. However, while hydroquinone works by inhibiting the activity of tyrosinase by acting as a melanocyte cytotoxic inhibitor and by increasing the cytotoxicity of melanocytes (melanin-producing cells), kojic acid lightens the skin solely by suppressing tyrosinase activity (by inhibiting catecholase activity of tyrosinase) in a non-traditional fashion. Kojic acid is revered worldwide for its skin-lightening abilities, and is commonly used in topical formulations to treat dark spots.
How effective is kojic acid?
Kojic acid is normally used twice a day for 1-2 months for the lightening of dark spots or the treatment of melasma. According to Baumann-cited studies by Ellis and Garcia, kojic acid combined with glycolic acid was more effective than 10% glycolic acid or 4% hydroquinone for the treatment of hyperpigmentation. A third Baumann-cited study by Lim et. al. found that 2% kojic acid in combination with 10% glycolic acid and 2% hydroquinone further improved melasma symptoms over a mixture of 10% glycolic acid and 2% hydroquinone alone.
Kojic acid, glycolic acid, and hydroquinone are all found in Age Advantage Laboratories Spot Life Serum ($41.34, Amazon.com). Unfortunately, the concentration of kojic acid, glycolic acid, and hydroquinone in this product has not been published, so the above studies may not apply. (No products could be found that publish 2% kojic acid, 10% glycolic acid and 2% hydroquinone). Age Advantage Laboratories Spot Life Serum also contains retinol and alpha lipoic acid (an antioxidant). Due to the fact that the product contains both glycolic acid and retinol, skin is more photosensitive after its use, and therefore a broad-spectrum UVA/UVB sunscreen should be applied when in particular when using this product.
Are there any side effects with Kojic Acid?
According to the Baumann-cited study by Lim et. al., kojic acid has been found to be associated with contact allergy and has a high sensitizing potential. For this reason, kojic acid is more commonly found in concentrations of 1% rather than 2.5%, but there are reports of sensitization to 1% as well (Baumann-cited, Nakagawa et. al.)
Although kojic acid has been established in a study by Burdock et. al. to be safe when ingested as a component of soy sauce, miso, sake, or as a food additive (it prevents oxidative browning and promotes reddening of strawberries), kojic acid was reported in the same study to induce convulsions if injected. For this reason, kojic acid should not be injected into the skin!
Are there any benefits to Kojic Acid over hydroquinone?
In terms of efficacy, no. In a recent review, a reported study found that kojic acid and glycolic acid in combination was reported to have the same efficacy in treating hyperpigmentation and melasma as hydroquinone and glycolic acid in combination. However, kojic acid was reported in the same study to be more irritating. A different study in the Journal of Cosmetic Dermatology further reported that kojic acid alone was less efficacious than 2% hydroquinone in treating hyperpigmentation.
Although kojic acid has been reported in the Brazilian Journal of Medical and Biological Research to exhibit some promising antioxidant properties, hydroquinone has been reported to have antioxidant abilities as well. Kojic acid is sometimes preferred because it has greater stability in cosmetic products than hydroquinone (Baumann-cited, Burdock et. al.). In fact, it has been established in a study by Burdock that hydroquinone should be stored at low temperature with the cap tightly sealed to preserve its effectiveness. In addition, kojic acid is sometimes preferred due to recent concern over a possible link between hydroquinone and ochronosis (skin darkening); however, according to a comprehensive review of 10000 patients by Dr. Jacob Levitt, the fears appear to be unfounded, particularly for those patients with lighter skin.
To hydroquinone’s advantage, hydroquinone is also not associated with the contact sensitization and irritation of kojic acid. Due to the established efficacy of hydroquinone and kojic acid in combination in the aforementioned studies by Ellis and Garcia, it seems most efficacious to use both in combination, most likely because it has been established in the Journal of Pigment Cell Research that hydroquinone and kojic acid inhibit tyrosinase activity in distinct ways.
So, in general, is kojic acid safe and effective?
Due to the potentially irritating effects of kojic acid and other lightening agents, be sure to talk to your dermatologist. Your dermatologist can prescribe specific treatments for you and your skin type. In general, kojic acid is associated with a high level of efficacy, particularly in combination with hydroquinone and glycolic acid. Kojic acid has also been reported in several studies to have a higher efficacy than arbutin in lightening the skin. However, due to the irritating nature of kojic acid, you may wish to try kojic acid on a small patch of skin first, in order to see how your skin reacts to the product.
What treatments are proven effective against hyperpigmentation?
*2% kojic acid, 10% glycolic acid and 2% hydroquinone (has been established to have higher efficacy than 10% glycolic acid and 2% hydroquinone without kojic acid). All three ingredients are found in Peter Thomas Roth Ultra Gentle Skin Lightening Gel Complex, with 2% hydroquinone and unknown concentrations of kojic acid and glycolic acid, and Age Advantage Laboratories Spot Life Serum, although the concentrations of all three ingredients are not known in the product.
*2% hydroquinone (over-the-counter strength) and 4% hydroquinone (by prescription).
*5% (or greater) L-ascorbic acid (vitamin C), although substantially less than 4% hydroquinone.
In general, based on the review, it may be inferred that Tri-Luma OR a combination of 2% kojic acid, 10% glycolic acid and 2% hydroquinone are more efficacious than 4% hydroquinone, which in turn is more efficacious than 5% L-ascorbic acid in treating hyperpigmentation. For optimal results, talk to your dermatologist!