Guide
Why Vitamin C Serum Turns Yellow or Brown (Oxidation)
By the BestCSerum editorial team · Updated 2 October 2026 · How we write and check content
What oxidation does
L-ascorbic acid is unstable in water-based formulas. When it oxidises it turns into dehydroascorbic acid and other breakdown products, which give the yellow-brown colour. Dermatology reviews also note that oxidised vitamin C can temporarily tint skin yellowish.
Derivatives such as sodium ascorbyl phosphate, magnesium ascorbyl phosphate and THD ascorbate were developed partly to be more stable.
Is an oxidised serum still usable?
Some brands deliberately tint their serums, so compare against the colour when you first opened it. If it has turned noticeably darker or smells different, it has lost much of its activity and is unlikely to give the results you bought it for.
How to store vitamin C serum
Close the cap straight after use, keep it out of direct sun and away from bathroom heat, and choose opaque or airless packaging. In hot Indian summers a cool cupboard helps. Buying a smaller bottle you can finish in a couple of months often makes more sense than a large one; compare by price per ml in our budget lists.
Frequently asked questions
+Should I keep vitamin C serum in the fridge?
It is not required, but a cool, dark place slows oxidation. Follow the storage instructions on the pack.
+Can oxidised vitamin C harm my skin?
It is mainly less effective and can leave a temporary yellow tint. If it irritates your skin, stop using it.
Related guides
- How to Use Vitamin C SerumStep-by-step guide to using vitamin C serum: when to apply it, how much, whether it goes before or after moisturiser and sunscreen, and how to avoid irritation.
- Vitamin C Serums Under ₹1,000Vitamin C serums priced up to ₹1,000 in India, compared by price per ml, bottle size, vitamin C form and sourced customer ratings.
- Vitamin C Serums for Dark SpotsWhich vitamin C serums suit dark spots, what kind of spots vitamin C can fade, how long it takes, and products compared by form, price and ratings.
Vitamin C forms mentioned on this page
Sources
General information only, not medical advice. This page has not been reviewed by a dermatologist. If you have a skin condition, are pregnant, or react to a product, speak to a qualified doctor. Product data is checked against named sources; see our methodology.