Does vitamin C serum need to be clear?

Why did my vitamin C serum turn orange?

Oxidation is a possible explanation, particularly if an ascorbic acid serum has changed from almost colourless to yellow and then looks darker. Ascorbic acid is unstable when exposed to oxygen and light; its oxidized form can give the serum a yellow colour. Orange is not a universal cutoff for every formula, so ask the manufacturer whether that change is expected for your exact product.23

Limit exposure to light and air, and follow the product's storage instructions. Packaging matters: Vanicream uses an airless pump to help prevent oxidation and colour change. COSRX The Vitamin C 23 uses a specialized bottle designed to release gas while blocking oxygen from entering. These are different approaches to protecting a formula, not reasons to transfer one product's storage rules to another.14

Does brown vitamin C serum mean it has oxidized?

A substantial colour change in an ascorbic acid serum raises concern about oxidation, but brown is not a universal test for every vitamin C formula. Colour alone cannot tell you how much active vitamin C remains. If your serum has turned brown, pause use and check with the manufacturer before continuing.2

A clear appearance is not a test of effectiveness either. Vitamin C needs a stable formulation and adequate delivery into the skin to work; some topical preparations contain too little or do not penetrate sufficiently. A clear bottle of serum is not a certificate of achievement.3

Why does vitamin C serum smell different after a few weeks?

An unusual smell from the start is different from a new smell developing later. COSRX The Vitamin C 23 contains no fragrance, and COSRX describes its characteristic vitamin C smell as normal and unrelated to potency. If the smell changes after a few weeks, ask the brand about that change rather than assuming its explanation for the original scent still applies.4

How should I use a serum with its normal colour?

Follow your formula's directions. Vanicream recommends once daily, morning or night, after cleansing and before moisturizer, sunscreen or makeup; its directions allow up to twice daily. For COSRX The Vitamin C 23, patch test before first use, reduce frequency if irritation develops, and stop if irritation persists. COSRX also advises against combining that serum with exfoliating hydroxy acids because of irritation.14