In Japan, there are values that prefer the state where the skin is white and has no spots or dullness. Therefore, spots and freckles are becoming one of the skin troubles for many consumers. The term “skin whitening” is used as a term referring to skin care for skin troubles such as spots and freckles. Products used for skin whitening purposes, so-called whitening products, generally refer to quasi-drugs containing skin whitening active ingredients. Various mechanisms of action for skin whitening have been elucidated so far, and various skin whitening active ingredients have been developed accordingly. In this article, the functional mechanism of skin whitening active ingredients blended in skin whitening quasi-drugs and the effects on human skin were outlined.