Natural sources of melanogenic inhibitors: A systematic review

Melanin gives some natural protection against the harmful effects of ultraviolet radiation; however, excessive production of melanin causes skin hyperpigmentation. Depigmenting cosmetics can be used to control this process; however, depigmenting agents commonly used have some disadvantages, such as low bioavailability, photosensitization, cellular toxicity, and insolubility. Natural sources of melanogenic inhibitors have become important alternatives to synthetic ones. The objective of this review was to summarize the results of studies on natural extracts that have been reported in the literature to inhibit the process of melanogenesis, giving a view on their suitability for potential use in new cosmetic formulations for skin-lightening.

A systematic literature search was carried out using the descriptors: "melanogenesis", "tyrosinase", "tyrosinase inhibition", and "natural agents".

Publications were selected based on our designated inclusion and exclusion criteria, and a total of 15 studies met these criteria.

The following were used in the review of each paper which met the criteria: the name of the plant (all of the natural extracts turned out to be from plants), the method used to obtain the plant extract, the method for evaluating anti-tyrosinase activity, the main results, and the conclusions.

All evaluated natural agents demonstrated anti-tyrosinase effect. The species Leathesia difformis, Morus alba, Orostachys japonicus, Heracleum moellendorffii, Coix lacryma-jobi (adlay), Inula brittanica, and Gailardia aristata stood out from the others due to their application as potential inhibitors of more than three proteins related to melanogenesis, including the cyclic adenosine monophosphate response element-binding protein, microphthalmia-associated transcription factor, tyrosinase, tyrosinase-related protein-1, tyrosinase-related protein-2, and dopachrome tautomerase.

The plants present an anti-tyrosinase effect that must be better explored in the new cosmetic formulations. The anti-melanogenic effects of the plant are mainly related to the presence of phenolic and antioxidant compounds.