What it is
Kojic Acid is a by-product of the manufacture of sake (rice wine)
What it does
Kojic acid is a skin lightener. It inhibits melanin production by blocking the enzyme essential for it, called tyrosinase. It lightens skin discolourations, such as age and dark spots, freckles, and melasma.
In addition, it has antioxidant properties.
Kojic acid is very unstable and oxidize rapidly. When it is exposed to air, it turns into a shade of brown and loses its efficacy.
In high concentrations, it can irritate skin.
In addition, it causes sun sensitivity as well, so you should always use a sunscreen before applying Kojic Acid.