Vitamin C (Ascorbic Acid)

What is vitamin C and what does it do?

Vitamin C is the skin's main water-soluble antioxidant. Applied topically, L-ascorbic acid neutralises free radicals generated by ultraviolet light and pollution, complementing sunscreen rather than replacing it. It is an essential cofactor for the enzymes that stabilise collagen, so it supports collagen production in the dermis, and it interferes with tyrosinase to reduce new pigment formation. Pure L-ascorbic acid is unstable and needs a low pH to penetrate, which can sting. Derivatives such as ascorbyl glucoside or sodium ascorbyl phosphate are more stable and gentler, but must be converted in the skin and may be less potent. Packaging that limits air and light matters. [1]

“Vitamin C helps neutralise free radicals from ultraviolet light and pollution, but it complements sunscreen rather than replacing it.”

Dr Sin YongOn topical vitamin C

What does the evidence show?

Laboratory and small clinical studies support antioxidant and photoprotective effects, and a systematic review of trials found topical vitamin C improved melasma and photoaging measures, although most studies were small, short and often combined vitamin C with other actives. Evidence for derivatives is thinner than for L-ascorbic acid. Overall, vitamin C is a reasonable supporting active with modest, gradual benefits rather than a stand-alone treatment.

Who should avoid vitamin C?

Low-pH L-ascorbic acid serums can sting or irritate sensitive skin, rosacea or eczema-prone skin; a derivative or lower strength may suit better. Discontinue if a rash develops. Oxidised products that have turned dark orange or brown are less active. People using strong exfoliating acids may prefer to apply vitamin C at a different time of day.

Is vitamin C available in Singapore?

Vitamin C and its derivatives are common cosmetic ingredients and are widely available in serums and creams sold in Singapore. Cosmetic products are notified to the Health Sciences Authority rather than individually approved, so stability and strength vary between brands. Oral vitamin C supplements are a separate category.

If a dark patch, breakout or irritation is not responding to what you are using, the next step is a diagnosis rather than another product. See the Skin A–Z library for related ingredients.