According to SK-II webpage:
High intensity treatment serum - the foundation of the Whitening Source range. Helps re-balance skin tone across three visual dimensions - translucency, evenness and radiance. Illuminates skin and creates more uniform tone with colour balancing moisturizers, giving a deeper and clearer appearance. Contains the highest concentration of our exclusive DermComplex.
I swear by SK-II whitening products, I've tried my share of whitening products and none has ever worked like SK-II. I mean other products still works, but it takes a long time to see any visible effects, while with SK-II, you'll need only about a week to really see a difference. It evens out and brightens your skin tone, it just make your skin look radiant.
The Whitening Source Derm Definition is no longer available in Asia, and it has been replaced by the Cellumination Essence which I've recently got a bottle for my mum, who came back from a trip super tanned. Let me tell you something about my mum, she's someone who doesn't care about skin care or makeup, but whenever she finishes her bottle of SK-II serum, she always tells me to get her a new bottle, I think that really does tell you how good this product is.
於亞洲已經買不到Whitening Source Derm Definition，它已被新出的 Cellumination Essence取代了，而小妹亦剛買了支給媽媽。小妹的媽媽是一位對化妝品及護膚品完全沒興趣的人，但每次用完支SK-II美日精華都會叫我去買過支新的，我想這應該足夠證明這支精華素真的不錯。