Vitamin C, also called ascorbic acid, is a popular natural ingredient used in skin care cosmetics. There are two mechanisms by which it can affect your skin.
Vitamin C is an essential component for collagen synthesis. Without adequate vitamin C, the collagen in your skin would be malformed and your skin and gums would not heal properly. This is obvious in patients who are clinically deficient of vitamin C, a condition called scurvy.
Vitamin C is a potent antioxidant. Like other antioxidants, it helps to prevent skin damage and wrinkles by soaking up harmful free radicals.
The problem is how to get the vitamin C into your skin. Your skin is designed to keep things out (on the whole, a good idea), but this makes getting medications and creams below the surface, where they exert their effects, rather difficult or simply impossible.
In order for vitamin C to penetrate the skin, it needs to be in an acidic environment, and it needs to be in a high concentration in the product. Unfortunately products that contain potentially effective concentrations of ascorbic acid would be very expensive.
In addition, topical vitamin C is highly degradable. When exposed to air it oxidizes and its free radical soaking capabilities are muted — it becomes an inert, yet nicely citrus fragranced cream.
It’s extremely unlikely with commercially available amounts of Vitamin C/ascorbic acid to have any measurable impact on your skin.