What is it? Kojic acid is a byproduct of fungus such as Aspergillus and Penicillium.
What is it for? Its skin whitening ability was discovered over 20 years ago; it lightens freckles, acne scars, melasma, and other forms of hyperpigmentation. Currently, it is available as a whitening agent in creams, soaps, lotions and ampoules. Other than for cosmetic purposes, it can also prevent browning of certain foods (potato, mushroom, apple, etc.) when exposed to air by inhibiting polyphenol oxidase.
How does it work? Kojic acid inhibits catecholase activity of tyrosinase. Tyrosinase is an enzyme needed for formation of melanin, your skin pigment. With kojic acid inhibiting this enzyme, there will be a decreased production of melanin and your skin will look lighter in a matter of weeks.
Want more details? Another way kojic acid works in vivo is through its involvement with NF-κB. In a cell, NF-κB is inhibited by a protein called IκB. With UV light and other activators, IκB degrades and NF-κB is freed and is able to translocate to the nucleus and affect expression of certain genes. One particular example of a gene expression it can change is that of melanotrophic factors, meaning NF-κB, when active, can cause increased production of melanin. In a study, several melanogenic inhibitors (niacinamide, kojic acid, hydroquinone, resorcinol, arbutin, and glycolic acid) were tested and kojic acid was found to be the most potent inhibitor of UVB-induced NF-κB activation. The inhibitory activity of kojic acid was also more potent than known antioxidants such as vitamin C and N-acetyl-L-cysteine.
Here in the Philippines, we have fanatics of whitening products and that is why many soaps here include kojic acid, too. One of the first few brands to be introduced in the market is Kojie San Skin Lightening Soap.
Caution: if you know that you have allergies to cosmetics, avoid kojic acid. It has a high sensitizing potential and patients allergic to it can develop contact dermatitis. Do a patch test first. Apply a small amount on a part of your skin and see if anything happens. With soaps, rub it on a small spot, leave it on for a few minutes and check for irritation. Do not use if you develop redness and itchiness.
From: Archives of Pharmacal Research and Journal of Dermatological Science