Kojic acid is a chemical produced by many species of fungus, including Penicillium, Acetobacter and Aspergillus. The Aspergillus flavus variety ferments sake wine and miso and shoyu -- soybean paste and sauce, which all contain kojic acid. According to researchers at Burdock and Associates in Vero Beach, Florida, reporting in 2003, in the journal "Regulatory Toxicology and Pharmacology," kojic acid works in dermatology applications by disrupting melanin skin-pigment biochemistry. Other actions are also known.
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Kojic acid inhibits many animal and plant enzymes. Primarily, it suppresses enzymes that remove oxygen from certain amino acids, polyphenols and xanthines. Some of these chemicals are used in making the dark skin pigment called melanin. Kojic acid competes with, and blocks, the natural enzymes that direct melanin production. But the competition is reversible, so the acid cannot permanently disrupt these important body functions. As a result, kojic acid applied to your skin blocks new melanin production, eventually lightening your skin. However, when you stop using kojic acid, melanin production can resume.
Kojic acid works to improve your complexion by fading dark, highly pigmented age spots, according to MayoClinic.com. Kojic acid creams and lotions, available over-the-counter, work slowly, over weeks or months, requiring daily applications. Kojic acid must penetrate your epidermis -- the topmost layer of skin -- where the extra pigment is made. Because kojic acid passes through healthy skin cells to work, it is often irritating. The European Commission's 2008 report by the Scientific Committee on Consumer Products ruled kojic acid unsafe based on how kojic acid works on healthy skin.
Kojic acid works by disrupting basic biochemical processes. Even though it works in a generally reversible manner, some evidence suggests it may be able to irreversibly alter your DNA. In a March 2010 study of 1,547 chemicals, Dr. Lois Swirsky Gold, Director of The Carcinogenic Potency Project, at The University of California Berkeley, detected the ability of kojic acid to create mutations in salmonella bacteria. This is interpreted as a potentially cancer-causing effect in humans. Kojic acid was also found to induce cancer in mouse thyroid glands. Exactly how kojic acid works mutate DNA is not understood. Consult your doctor before you try kojic acid skin lighteners.
Chemists at Peakchem.com report that kojic acid and other chemicals derived from it work as antioxidants to prevent food spoilage. Because kojic acid works by preventing oxidation, it is also used as an antiseptic agent and preservative, killing and preventing growth of bacteria by interfering with their normal oxidative metabolism. This antioxidant ability also makes kojic acid a useful color stabilizer in the processing of meat.
Due to its historic and traditional, apparently safe, food uses, kojic acid is considered acceptable in many applications. However, the FDA cites kojic acid's instability -- it deteriorates in air and light -- and its irritant quality as reasons to develop sensitive laboratory tests for its presence and limit its concentration to 0.2 to 1 percent in products for human use. It works in a broad variety of chemical reactions, in addition to melanin suppression, giving it other useful properties, according to Peakchem.com. In the mouth, it works as a whitening agent for teeth. Antioxidant action makes it a color stabilizer and freshness preservative for cut-flowers. Kojic acid also works as a preservative in the preparation of the antibiotic cephamycin. It can also work as a pain killer and anti-inflammatory agent.