Like most others have reported, this has made a heckuva big difference in my skin. Many, many moons ago, my first MAC studio fix was NC15. A few years later, I'd moved up to NC20. Then fast forward another decade, and I was NC25. Clearly some long term darkening and sun damage going on, despite my using European sunscreen or IT CCcream religiously. Reading about vitamin C from the lovely skincare board ladies, and youtube videos like Uppiesbeads59 (who also provides a handy mixing chart), I ordered vit C powder from Garden of Wisdom, and went to town mixing it up with rose water and glycerin. Started using it nightly about a year and a half ago. After about 6 months, the NC25 was looking a bit dark, but still doable. Then, excited at my progress, I plunged into Japanese sunscreens last summer. Also courtesy of the skin care board sages. So for the past year I've used the vit C and either Biore or IT CC on any given day. This spring I pulled out the old MAC NC20, and it looked a much better fit than the NC25. Just a few weeks ago, and this is summer, mind you, I took a gamble on a very old NC15 compact. And, yeah, it looks just fine. The NC25 (and other foundations similar in color) that matched me just 2 years ago now look so dark.
So, yeah, combo of better sunscreen and - equally important- the vit C serum is turning back the clock on my sun damage. And another bonus: it's wonderfully inexpensive to make, as well. I may not be 25. I may not look 25. But at least my skin color is 25 again!