Vitamin C (Ascorbic Acid)
What it does
Vitamin C is a well-known antioxidant. In skincare it helps neutralize some of the daily environmental stress that dulls skin, visibly brightens and evens tone, and supports collagen for a firmer look. The most potent and studied form is L-ascorbic acid, though several gentler derivatives exist.
What to know
Pure ascorbic acid is effective but can be unstable — it oxidizes with exposure to light and air, which is why serums may darken over time and are often sold in opaque bottles. It pairs especially well with morning sunscreen, since its antioxidant action complements SPF. Higher concentrations can feel tingly on sensitive skin, so gentler derivatives may suit better.
Commonly found in
Morning serums, brightening treatments, and antioxidant moisturizers.
Frequently asked questions
What does vitamin C do for skin?
It is an antioxidant that helps defend against daily environmental stress, brightens and evens tone, and supports collagen for firmer-looking skin.
When should I apply vitamin C?
Many people use it in the morning under sunscreen, where its antioxidant protection complements SPF. It can be used at night too.
Why does my vitamin C serum change color?
Pure ascorbic acid is potent but can be unstable and oxidize over time, turning yellow or brown. Gentler, more stable derivatives are also available.
Evidence
Last updated: August 5, 2026