Vitamin C (L - Ascorbic Acid) C5 H8 O6

Potentially vitamin C can benefits the skin in two important ways. Firstly, it is essential for synthesis of collagen. Secondly it is an antioxidant and can help reduce skin damage caused by free radicals.
It has also been demonstrated to moderately protect against UVB photo damage as well as UVA phototoxic responses.
Vitamin C has ability to regenerate the lipid soluble Vitamin E. combination af vitamin C and vitamin E offer greater protection against UVA and UVB exposure than ether anti oxidant alone.
Vitamin C helps speed s up reproduction of fresh skin cell for scar
Water based vitamin C may store well but would be oxidized on the face soon. In the presence of air and oxidizing agents, vitamin C is easily converted to oxidized forms. The oxidized form is not only ineffective but also may promote free radical formation causing damage to vital molecules such as protein and DNA. Only highly concentrated preparations (10% or more, pH should be below the ascorbic acid pKa which is 4.2) deliver enough vitamin C to the cells to be topically effective. At this concentration, vitamin C is highly acidic (pH around 2.5), which may be irritating. Neutralizing the acidity does not solve the problem because buffered vitamin C become ionized, which reduce skin penetration. There are some practicable approaches to solving the above problems.

Anhydrous vitamin C
In this way a topical base cream contains no water. Since water acts as a catalyst for vitamin C oxidation, anhydrous environment reduces the rate of vitamin C degradation. Anhydrous vitamin C is more stable not only during the storage but also on the skin after the application. Anhydrous form tends to be less irritating than regular ascorbic acid products, because the irritation is caused by hydrogen ion generated by acid dissociating in water.

Vitamin C derivatives

They tend to be more stable and less irritating but some people who respond to vitamin C did not respond to its derivatives. So far two compounds have found their way in to the broad skin care market: ascorbyl palmitate and magnesium ascorbyl phosphate.

Ascorbyl palmitate: It is fat - soluble derivative of vitamin C in skin care. It is non irritating and more stable than vitamin C. it is fat soluble antioxidant and is at least as effective as vitamin E in protecting the skin from lipid peroxidation. But it appear that the concentration of ascorbyl palmitate achievable is skin care formula does not boost collagen synthesis as much as vitamin C. when buying products with vitamin C or any vitamin C derived, it is the best to choose colorless or white formulation.

Fe 3+ + ascorbate --------------à Fe2+ + dehydroascorbate

Fe2+ + H2O2 --------------------à Fe 3+ + OH- + OH.