When looking at the ingredient list, if you want a pure form of vitamin C, go for a vitamin C serum that utilizes L-ascorbic acid as the main form of vitamin C. “Known as the purest form of vitamin C, L-ascorbic acid helps neutralize free radicals, minimize the look of fine lines and wrinkles, and brighten skin tone,” says Mona Gohara, MD, associate clinical professor at Yale.
If you have more sensitive skin or just want a more stable form of vitamin C, Zeichner recommends vitamin C esters instead of the pure form. “Vitamin C esters are an oil-soluble form, which tend to be less potentially irritating and more stable in cosmetic formulations,” he says. “Examples include sodium ascorbyl phosphate and THD ascorbate. Many are light stable and come in clear bottles.”