Kojic acid is a compound that is commonly derived from various fungi. Kojic acid is often used as a skin lightening agent because of its effects on a protein known as tyrosinase. According to Dr. Alaina J James at the University of Pennsylvania Medical Center, kojic acid works by preventing a specific function of tyrosinase called its catecholase function. The important thing to understand about the catecholase function is that it is the most important step in making the compound melanin. Melanin is the primary pigment in skin. Thus, by inhibiting the tyrosinase protein's ability to make melanin, kojic acid is able to prevent skin pigmentation, which can help lighten the skin's tone.
Kojic acid, according to both Dr. James and the website Smartskincare.com, is an effective treatment for the lightening of skin and has similar effectiveness as another commonly used skin lightening agent, hydroquinone. However, smartskincare.com does note a potential problem with using kojic acid. Kojic acid is relatively unstable, which means that it will react with oxygen and sunlight, causing it to change as a chemical compound. As a result, kojic acid is often packaged as kojic acid dipalmitate, which is a modified form of kojic acid. Although this form is more stable, it is not clear as to whether or not it is as effective as regular kojic acid.
Kojic acid is often administered as part of a topical gel that contains 1 to 4 percent kojic acid. One of the side effects of these formulations is that they can irritate the skin, causing an itching and painful rash known as contact dermatitis. As a result, kojic acid is often packaged with corticosteroids to help prevent this contact dermatitis. Kojic acid is often packaged with other chemicals besides corticosteroids, such as hydroquinone, in order to increase its effectiveness.