Kojic acid
Chemical name: 5-hydroxy-2-hydroxymethyl-1,4-pyrone
Molecular Formula: C6H6O4  
Molecular Weight: 142.11
Structural Formula:
Kojic acid is a chelation agent produced by several species of fungi, especially Aspergillus oryzae, which has the Japanese common name koji.Kojic acid is a by-product in the fermentation process of malting rice, for use in the manufacturing of sake, the Japanese rice wine. It is a mild inhibitor of the formation of pigment in plant and animal tissues, and is used in food and cosmetics to preserve or change colors of substances. It forms a bright red complex with ferric ions.
Application:
(1) Cosmetics: Kojic acid, (5-hydroxy-2-hydroxymethyl-1,4-pyrone,  is used for macula-removing and whitening.In the human skin, tyrosine is oxidized and polymerized with oxygen-derived free radicals under the catalytic action of tyrosinase and then synthesized to melanin. Kojic acid can inhibit tyrosinase synthesis, so it can largely inhibit the skin melanin formation; furthermore, kojic acid is safe and nontoxic and won’t cause white spot syndrome. Therefore, it has been widely added into the lotion, face mask, liquid cream and skin cream. Whitening cosmetics containing kojic acid are able to treat effectively the freckle, senile plaque, pigmentation and acne, etc. Kojic acid in concentration of 20ug/ml is able to inhibit 70~80%of the activity of many kinds of  tyrosinases (or polyphenoloxidase PPO) .
recommendation usage for cosmetics: 0.2~1.0%.
(2) Raw Materials:  Kojic acid, (5-hydroxy-2-hydroxymethyl-1,4-pyrone,  is the mateial for making maltol and cthyl maltol.
(3) Medicine: Kojic acid, (5-hydroxy-2-hydroxymethyl-1,4-pyrone,  has no mutagenic action to eukaryotic cells. It is able to eliminate the free radicals in the human body, strengthen the activity of the leucocyte, so it is good for human health. Now kojic acid has been used as the an important material of cephalosporin-type antibiotics. The finished products have ideal effect in easing pain, relieving inflammation and curing many diseases (like headache and toothache, etc.).
(4) Agriculture: Kojic acid, (5-hydroxy-2-hydroxymethyl-1,4-pyrone,  is used in producing biological pesticides. 0.5-1.0% of kojic acid can be added in microelement fertilizer (crimson liquid). This kind of crop production promoter has significant effect on increasing production of grains and vegetables, no matter it is used as low-concentration foliage fertilizer for spraying or yield-increasing agent for root applying.
(5) other fields: Kojic acid, (5-hydroxy-2-hydroxymethyl-1,4-pyrone, is also used as iron analytical reagent and film spotting agent, etc.