What percentage of Vitamin C is most effective?

Vitamin C is most effective in the 10–20% concentration range. Below 10%, you may see antioxidant benefits but minimal brightening or collagen-stimulating effects. Above 20%, efficacy does not increase significantly and irritation risk rises. A 15% L-ascorbic acid serum at the correct pH below 3.5 is considered the gold standard for most skin types.