Vitamin C

What does vitamin C do for skin?

Vitamin C is the ingredient people buy for a brighter, fresher look. Picture skin that looks flat and a little grey, faint brown patches from past summers, and fine crisscross lines on the chest or the backs of the hands. Those are the signs it was studied on.

In a 6-month double-blind trial, women with sun-worn skin on the chest and arms put a 5% vitamin C cream on one side and the same cream without vitamin C on the other. A dermatologist and the volunteers both rated the vitamin C side better overall. Skin replicas showed a finer, denser surface texture and fewer deep furrows, and tissue samples showed repair of the stretchy fibers under the surface.

How does vitamin C work?

It does two jobs. First, it is an antioxidant: sunlight creates unstable molecules in skin that wear down collagen, and vitamin C mops them up. Second, it supports collagen, the springy protein that keeps skin firm. A 2017 review adds a third effect on color: “It decreases melanin formation, thereby reducing pigmentation.” In plain terms, it can soften the look of brown spots over time.

Why does the formula matter so much for vitamin C?

Pure vitamin C breaks down easily and struggles to get into skin, which is why two serums with the same percentage can behave very differently. In a skin-absorption study, L-ascorbic acid only entered the skin when the formula was more acidic than pH 3.5. Absorption peaked at 20%; going higher did not help. Skin levels filled up after 3 daily applications and took about 4 days to fall by half after stopping. Three popular derivatives, including magnesium ascorbyl phosphate, did not raise vitamin C levels in that test.

Pairing matters too. Adding ferulic acid to a serum of 15% vitamin C and 1% vitamin E made the mix more stable and doubled its protection against simulated sunlight in the lab, from about 4-fold to about 8-fold. That was measured as less redness and fewer sunburned cells, not as an SPF, so it does not replace sunscreen. For strength choices, see which vitamin C percentage to pick.

How long until you notice a difference?

In the 6-month trial, changes were assessed at 3 and 6 months. Think in months, not weeks, for texture and lines.

How do you use vitamin C?

Because part of its studied benefit is protection against sunlight, a morning layer after cleansing and before moisturizer and sunscreen makes sense. It can be layered with niacinamide; see using niacinamide and vitamin C together.

Who should be careful with vitamin C?

The 5% cream in the 6-month trial was well tolerated. Serums that rely on a low pH to work are a different formula, so patch test a new one before putting it all over your face. A 2023 review of 7 clinical studies also found that every one tested vitamin C together with other ingredients or methods, so no product can promise results from vitamin C alone.