Vitamin C molecule

Vitamin C, also known as L-ascorbic acid, interferes with pigment synthesis at various oxidative steps of melanin production.

It has a reducing effect and can alter melanin from jet black to light tan.

Vitamin C interferes with melanin synthesis by reducing oxidized dopaquinone, interrupting DHICA oxidation and interacting with copper ions at the active site of tyrosinase.

Vitamin C acts as an Reactive Oxygen Spieces scavenger by donating electrons to neutralize free radicals found in the aqueous compartment of the cell.

One of the disadvantages of Vitamin C is its chemical instability in aqueous solution and its tendency to oxidize and denature. The hydrophilic nature of Vitamin C also limits its skin penetration, unless the stratum corneum barrier is disrupted. 

The more stable ascorbate ester, magnesium-l-ascorbyl-2-phosphate (MAP) is more lipophilic and has a greater permeation through the stratum corneum.