Most likely you've either seen, heard or read about the benefits of vitamin C. Its external use has had fairly good evidence of successfully fighting fine lines and wrinkles. But before you get too excited and run out to throw your money at anything that claims to have this, take a closer look.
The process to get the proper and helpful form of the vitamin is actually a lot trickier than advertising makes you think. It's difficult because it's so unstable when exposed to air. When it is exposed, vitamin C starts to oxidize (this means its molecules begin to change, altering the original form of the vitamin) making it ineffective and even actually harmful to skin.
So what exactly does Vitamin C do? Well, it's an antioxidant that helps to eliminate free radicals from the skin. Free radicals are molecules which are unstable and age the skin. These are commonly from smoking, pollution and the sun. Now the nature of an antioxidant is when exposed to sunlight or oxygen, it starts to break down and deteriorate, which makes it lose its effectiveness...and this makes it hard to keep in the form that benefits skin.
So now what? Well, vitamin C can be stabilized, but when saying "stabilized", it's actually just slowing the process of oxidation more than the normal rate. Cosmetic/beauty companies do stabilize their products, but by the time you buy and use them, they still may be badly oxidized. Vitamin C products are not cheap either, and if you find some that are, definitely reconsider it carefully! If it hasn't been stabilized properly, you're more likely harming your skin than helping it.
I personally use vitamin C directly from the fruit and right away. If you have a beauty recipe that calls for a citrus juice of any kind, try to get it straight from the fruit. Be sure to test it before using. It'll be much more beneficial for your skin!