Peter Thomas Roth Potent-C Vitamin C Power Serum The popular Peter Thomas Roth Potent-C Vitamin C Power Serum ($98) features 20 percent THD ascorbate, which is an extra stable form of vitamin C that can be up to 50 times more powerful than the traditional version. This serum helps improve uneven skin tone and texture, while also counteracting ageing and dullness in your complexion. Image Source: sephora.com Peter Thomas Roth Potent-C Vitamin C Power Serum $98 from sephora.com Buy Now