Out of the more than 900 Citrus species known today, Citrus Unshiu is a seedless, easy to peel tangerine coming from the Japanese town Satsuma. The peel extract used in cosmetics is mainly created from the "press-cake", the by-product of the juice industry and as it turns out, what's waste to one industry is a useful ingredient to another.
In cosmetics, the main thing of the Citrus Unshiu Peel Extract is being a skin-brightening or whitening agent. In-vitro (made in test tubes) and animal studies both show promising results for inhibiting tyrosinase, the famous enzyme regulating melanin production. It also contains antioxidant components such as carotenoids, coumarins, limonoids, and flavonoids that might be useful for the skin to protect itself from UV caused damages.
The downside of citrus peel extracts (that prevents our goodie rating) is that they usually contain some amount of essential oil components, though the amount is probably way too low to worry about unless you're super-duper sensitive.
Show me some proof
- Kim, Sang-Suk, et al. "Citrus peel wastes as functional materials for cosmeceuticals." Journal of Applied Biological Chemistry 51.1 (2008): 7-12.
- Kim, Sang Suk, et al. "Down-regulation of tyrosinase, TRP-1, TRP-2 and MITF expressions by citrus press-cakes in murine B16 F10 melanoma." Asian Pacific journal of tropical biomedicine 3.8 (2013): 617-622.
- ORYZA OIL & FAT CHEMICAL CO., LTD. , CITRUS UNSHIU EXTRACT: Health Ingredient for whitening and aesthetic, Ingredient for cosmetics