Vitamin C good for skin, but why doesn't all products work? Here's how to pick right product

Dermatologists often recommend vitamin C serums and creams for their potential benefits in brightening and firming the skin, protecting it from damage, and reducing signs of aging. However, research on the effectiveness of vitamin C on the skin has yielded mixed results. The problem is that although vitamin C is probably good for the skin, it's hard to make a product that works the way it's supposed to.