Vitamin C can also be effective at inhibiting melanin production. However, the tests that show it to be effective have used a concentration of over 5%, which is much more than what is usually used in cosmetic products. Vitamin C is also notoriously unstable, which means that by the time a cosmetic product containing it gets home to you it may have broken down and become useless. For this reason, Vitamin C is a last resort skin whitening treatment for those who can’t use the other topical treatments for one reason or another. It is also the cheapest product since you can also get it from extracts.