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Ingredient glossary
Vitamin C: What It Is and What It Does
Vitamin C is an antioxidant ingredient used in skincare, most often as L-ascorbic acid or a more stable derivative, to help defend skin against everyday environmental stress and support a brighter-looking complexion. It is typically applied in the morning under sunscreen and is notably unstable, oxidising on exposure to light and air.
What it does
As an antioxidant, vitamin C helps neutralise free radicals generated by everyday environmental exposure such as UV and pollution, which is why it is commonly paired with — never as a substitute for — daily sunscreen. It is also widely used for its role in supporting a more even, brighter-looking skin tone over time. Because it oxidises readily, a vitamin C serum that has turned yellow, orange or brown has likely lost much of its effectiveness and is past its useful life.
Who it suits
Vitamin C tends to suit people looking to support skin brightness and address environmental dullness, and is often used across normal, oily and combination skin. Sensitive skin can sometimes find L-ascorbic acid, the most common and potent form, irritating, in which case a gentler derivative such as sodium ascorbyl phosphate is often better tolerated.
Cautions
Vitamin C, particularly as L-ascorbic acid, can sting or cause redness on sensitive or compromised skin, and is best introduced gradually. It oxidises on exposure to light and air, so opaque or airless packaging and correct storage matter for how well it keeps. It is not a substitute for sunscreen. Anyone with persistent irritation should stop use and consult a pharmacist or dermatologist.
Products with Vitamin C
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Frequently asked questions
- When should I apply vitamin C in my routine?
- Most commonly in the morning, after cleansing and before moisturiser and sunscreen, since its antioxidant role is often framed around supporting the skin through the day's environmental exposure. Some people prefer an evening routine instead — either can work.
- Why has my vitamin C serum turned orange?
- That colour change is oxidation, and it means the vitamin C has broken down and is likely far less effective than when fresh. It is not harmful to use, but it is no longer doing the job you bought it for, and it is worth replacing.
- Can I use vitamin C with retinol?
- Many people alternate them — vitamin C in the morning, retinol in the evening — rather than layering both at once, since combining two potent actives increases the chance of irritation, particularly on sensitive skin.
This is general information about a cosmetic ingredient, not medical advice. It does not describe any specific product, and does not diagnose, treat or cure any condition. If you have a persistent skin or scalp concern, speak to a pharmacist, GP or dermatologist. See our editorial policy for how we handle claims.