I've been using a vitamin C serum on my face for about 3 years now. I've switched brands a few times, not because I felt a product didn't work. Vitamin C is always effective. How effective, is determined how the active ingredient is stored, then delivered to your skin. It use to be that serums with vitamin C, that also had water in the serum, made the vitamin C, not stay active long enough to sink into your skin layers. Deeply. The vitamin C, would deteriorate quicker, than if the C, were in a serum, without water. Layely, technology has been able to micro-encapsulate active ingredients so they dont decay before the ingredients can work. This Paulas Choice Resist C15 Super Booster has really brightened my face. Im sure that over time, more dark spots will fade. In just a few short days, I can see one on my neck, deminishing. The product isnt oily on your skin. It does absorb nicely.