I've been taking follic acid as one of my regular supplements for about two years or so, now. A couple of years ago, I ran into a friend who had had bad melasma patches on her nose and cheeks. They'd cleared completely and she told me her doctor had put her on follic acid. She also remarked that my melasma had started to clear.
Two years later, my melasma has gone. Try it. It's harmless, it works for a number of different other conditions and it will cure your skin problems.