Kojic acid is a substance produced by fungi belonging to the species Aspergillus oryzae, koji in Japanese. In particular, this species of fungi is responsible for the fermentation of malting rice for the production of sakè. A by-product of this process is, in fact, the kojic acid. Kojic acid is considered a healthful substance since it acts as an antioxidant, antimicrobial, antiviral, antiparasitic and antidiabetic, but it is also an important cosmetic ingredient included in the formulas of face creams, body, soaps and even toothpastes for its exfoliating power and its ability to fight the skin spots, caused, for example, by acne, melasma, lentigo (Saeedi et al, Biomed Pharmacother, Feb 2019). The spots on the skin may be due to many factors, such as excessive exposure to sunlight without adequate protection, aging, inflammation and hormonal imbalances. The kojic acid acts on the formation of these spots by inhibiting the synthesis of tyrosinase, an enzyme that is at the basis of the production of melanin, the pigment that gives color to the skin (Cabanes et al, J Pharm Pharmacol, Dec 1994). The effectiveness of kojic acid as a whitening of skin spots can be proven by several studies, such as the work published in 1999 in the journal Dermatologic surgery and conducted by the National Skin Care Center in Singapore (Lim et al, Apr 1999). In particular, the products containing 2% kojic acid were found to be effective in attenuating melasma, a condition in which brown or dark brown spots are usually observed on cheeks, chin and upper lip, in 60% of the cases analyzed against 47% of the cases treated with products without this substance but with only glycolic acid. The side effects reported, common, in any case, to all the whitening products, were irritation and burning. The kojic acid concentration should not exceed 2%, the threshold considered safe. In fact, the kojic acid is absorbed to a minimum extent by the skin but some studies seem to indicate that in case of very high concentrations of this substance, a condition that cannot be found if the threshold in cosmetics is respected, a protumoral action may be observed (Burnett et al, Int J Toxicol, Nov-Dec 2010). Apart from this observation, which does not concern controlled and certified creams and lotions, kojic acid proves to be a useful and effective substance to lighten skin spots.