Kojic acid is a natural substance that is derived from fungi, particularly the species Aspergillus oryzae, which is known as koji in Japan. It is used as an exfoliating and skin lightening ingredient in skincare products. Kojic acid is normally mixed in creams with a concentration ranging from 2% to 4%. It is sometimes also included in soaps or skin lotions.
Kojic acid is a chelation agent, which is to say that it binds with unwanted chemicals in the skin to inhibit their functioning. In particular, it binds with tyrosinase, a chemical that regulates the production of melanin in the skin. Melanin is responsible for the creation of freckles and age spots, hyperpigmentation (blotches), and dark skin colors. When kojic acid reduces the function of tyrosinase, less melanin is produced, and the skin becomes lighter in color, reducing the appearance of spots and heavily pigmented areas and evening out the skin tone. Some research also suggests that kojic acid can work to prevent wrinkling caused by excessive sun exposure. It can also help remove dirt and oil from the skin, reducing the frequency of acne breakouts. Kojic acid is not as strong as some other skin-lightening products, such as hydroquinone. It can take three months or more to have full effect and for dark areas to fade. However, its advantage is that it is milder and organically produced, so it does not have the harsh side effects that some artificially produced lighteners have.
Kojic acid normally has only mild side effects, and the weak concentration used in skincare products is generally not enough to be harmful. In people with very sensitive skin, kojic acid can produce irritation and dermatitis (red, bumpy, itchy skin). Some kojic acid creams include corticosteroids in order to prevent this sort of allergic reaction. If this reaction occurs, stop using kojic acid until your skin returns to normal. Kojic acid can also make skin more sensitive, but this can often be alleviated by switching to a product with a lower concentration. Kojic acid should not be used on skin that is broken, peeling, or already irritated. Like other skin lightening products, it can make the skin more sensitive to sunlight, so take care to limit your exposure to the sun and ultraviolet radiation.
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