What is it? Touted as one of the most effective topical agents against wrinkles and fines lines, vitamin C, or L-ascorbic acid, is vital for collagen production and the reduction of free radicals - natural by-products of oxidation that can be triggered by pollutants, sunlight, stress, smoking and excessive alcohol consumption. Left untreated, free radicals damage surrounding healthy cells and cause accelerated aging, damaged skin and even cancer.

Another form of vitamin C, vitamin C ester is also used in skincare products. Theress debate over which forms of vitamin C are more stable and beneficial. According to our skin care expert, Dr. Nelson Lee Novick, cosmetic dermatologist and dermasurgeon, “L-ascorbic acid, which is water-soluble and considered the most active form of the vitamin, is notoriously unstable in topical preparations and stability has only been achieved, to my knowledge, in a few patented formulations. On the other hand, fat soluble vitamin C (or ascorbyl palmitate) is more stable. It also tends to be somewhat less irritating. The comparative efficacy of the water and fat soluble forms in topical preparations remains something of a gray area. Manufacturers of latter contend that their products not only provide superior protection from free radical damage but are more effective regenerators of depleted vitamin E. I believe the jury is still out on these issues and more research needs to be done in this area.”

You'll find it in: Although oral ingestion of vitamin C is important for your health, the body eventually flushes it out, so applying topical vitamin C is your best bet for getting the skincare benefits.

Vitamin C is included in a bevy of skincare products, including anti-aging formulas, cleansers, serums and moisturizing products.

Ready to buy a vitamin C product? Keep in mind that when vitamin C is exposed to air, it undergoes oxidation and renders the product ineffective. According to Smart Skin Care, if the formulation has turned a yellowish-brown color, toss it. The unpleasant shade indicates that the product has oxidized and is therefore useless or even harmful, as vitamin C in its oxidized form might increase the development of free radicals.

Avoid the possibility of purchasing an unstable vitamin C product by choosing from a trustworthy brand, checking the expiration date and packaging and always storing it properly. In addition, select products with 10 percent of vitamin C or more.

Our product picks: For a revolutionary anti-aging product packed with antioxidants, try SkinCeuticals C E Ferulic. To help reduce the appearance of fine lines, wrinkles, age spots and sun damage, give SkinMedica TNS Recovery Complex Best Results Kit a try. Cellex-C High Potency Serum is another powerful anti-aging product, which contains 10 percent vitamin C.

What to expect: Though research is being done to develop a more stable formula of topical vitamin C, studies have shown vitamin C might play a role in protecting against UV damage and sunburn and activating collagen production. In the meantime, as mentioned above, not all vitamin C products are created equal; many of the products on the market contain low concentrations of vitamin C and don't even penetrate the skin, so you might not get the results you were hoping for. It’s important to be especially diligent when choosing a vitamin C product that actually works.

Who should avoid it: According to Dr. Novick, “Some of the water soluble vitamin C products can be slightly irritating, especially to dry or sensitive skin. But this of course is an individual response, as it is with the use of any cosmeceutical or cosmetic.”