Vitamin C is a popular ingredient in topical skincare products. The idea behind this being that it has antioxidant activity, and so may prevent the oxidative damage which can cause skin aging.
Vitamin C might also have a positive effect on pigmentation, so products including this ingredient are marketed as being effective for improving skin tone and reducing signs of dark spots.
There isn’t enough evidence to support whether or not vitamin C treats acne. Some studies have shown positive effects on reducing acne lesions and oil production when used orally. Topical use of vitamin C in acne has also shown positive results, but no studies have compared it to standard treatments yet.