Kojic acid is made from several different types of fungi. It’s also a byproduct when certain foods ferment, including Japanese sake, soy sauce, and rice wine.
Kojic acid inhibits and prevents the formation of tyrosine, which is an amino acid that’s needed to produce melanin. Melanin is the pigment that affects hair, skin, and eye color. Because it inhibits the production of melanin, kojic acid can have a lightening effect.
Kojic acid is often used topically to treat a number of different cosmetic conditions. It’s been approved for use in cosmetic products in concentrations of 1 percent or less. It’s most often used as a skin-lightening agent.
Kojic acid can be found in a number of different types of cosmetic products, including powders, serums, creams, cleansers, and soaps. Powders should be mixed with water or lotion, depending on the product instructions. Some products, like soaps and cleansers, are meant to be washed off immediately. Others, like creams and serums, are designed to be left on and absorbed into the skin. (However, kojic acid overall has relatively poor absorption rates below the surface of the skin.)
Some products — like face masks — are designed to be used only on occasion. Creams and cleansers may be used daily.
Products containing kojic acid are most commonly used on the face and hands, but can be used on all non-sensitive areas of the body.
Contact dermatitis is the most common side effect of kojic acid. It can manifest itself as redness, irritation, itchiness, rashes, swollen skin, or pain and discomfort. Contact dermatitis is most common in those with sensitive skin, or in individuals using a product with a higher concentration than 1 percent of kojic acid. Discontinue use if you’re reacting to a product with kojic acid in it.
Over time, long-term use of kojic acid may make your skin more susceptible to sunburn. Keep this in mind, and be particularly mindful of using sunscreen or wearing protective clothing.
You should never use kojic acid on damaged or broken skin. Some countries have banned this product because of a potential connection to the development of cancer. Further research is needed to identify and understand any other potential side effects.
Kojic’s acid primary use — and benefit — is to lighten visible sun damage, age spots, or scars. This can result in an anti-aging effect on the skin.
In addition to skin-lightening effects, kojic acid also contains some antimicrobial properties. It may help fight off several common types of bacterial strains even in small dilutions. This can help treat acne caused by bacteria in the skin. It may also lighten scars from acne that haven’t faded yet.
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When using kojic acid topically, you’ll likely start to see results within two weeks. You may see greater results — or faster results — if you also add glycolic acid to the treatment.
You can use kojic acid to treat areas of hyperpigmentation or scarring, but you shouldn’t use it in an attempt to lighten your natural complexion.
If you want to use products containing kojic acid to treat a certain condition or cosmetic appearance, make an appointment to see your dermatologist. They can help you decide about the best and safest course of action. They can also provide you with information about dosage and complementary treatments.
If you experience any redness, rashes, irritation, or pain when using kojic acid, stop using it immediately. To soothe immediate irritation, you can apply over-the-counter hydrocortisone cream to the affected area.