What it is
Kojic Acid is derived from a mushroom.
What it does
Kojic acid is a skin lightener. It inhibits melanin production by blocking the enzyme essential for it, called tyrosinase. It lightens age and dark spots and skin discolorations. It can be used on freckles and is also effective in treating melasma (irregular sized dark brown or grey patches on skin).
It also has antioxidant, antibacterial and antifungal 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.
It can also be very irritating to skin and can result in contact dermatitis and erythema.
It causes sun sensitivity as well, so you should always use a sunscreen before applying Kojic Acid.