The Vitamin C Guide

What vitamin C does

Vitamin C is an antioxidant that helps defend skin against daily damage from free radicals. In skincare it is valued for three things: brightening dull skin and fading uneven tone, supporting collagen for firmness, and adding antioxidant protection that complements sunscreen.

Vitamin C is a daytime workhorse in a lot of routines because it does several useful jobs at once and pairs neatly with sunscreen. It will not transform skin overnight, and it is not a treatment for a specific condition, but as a steady antioxidant and brightening step it earns its place. The main thing to get right is a stable form and good storage.

The main forms

Not all vitamin C is the same:

• L ascorbic acid. The pure, most studied form. Effective but less stable, so it can degrade with light and air.
• Derivatives such as sodium ascorbyl phosphate, magnesium ascorbyl phosphate and tetrahexyldecyl ascorbate. These are more stable and often gentler, which can suit sensitive skin.

Both can work. Derivatives trade a little strength for stability and tolerance.

Whichever form you choose, consistency is what delivers results. Vitamin C is a daily habit rather than an occasional treatment, so a product you enjoy using and can afford to repurchase will beat a stronger one that sits unused. Match the form to your skin and your routine.

How to use it

• Use it in the morning, after cleansing and before moisturiser and SPF.
• Pair it with sunscreen, since the two protect the skin in different ways.
• Store it away from light and air, and watch for it turning dark, which signals it has oxidised.
• Introduce it gradually if your skin is sensitive.

Pairing with other ingredients

Vitamin C works well alongside sunscreen and hydrating ingredients. It also pairs with niacinamide, despite an old myth to the contrary. If you use strong actives like acids or retinol, many people keep vitamin C in the morning and those actives at night to keep the routine simple. See the niacinamide guide and the retinol guide.

How to tell if it is working

Vitamin C works gradually, so give it time. Over several weeks of consistent morning use, you may notice brighter, more even looking skin and a fresher tone. It is a supporting player for antioxidant protection during the day rather than a dramatic overnight change.

Watch the product as well as your skin. Vitamin C that has turned deep yellow or brown has oxidised and lost potency, so store it away from light and air and replace it when the colour shifts. If a formula stings, try a gentler derivative or a lower concentration.

Choosing a product

Look for a form that suits your skin, packaging that limits light and air, and a concentration you can tolerate. Higher strength is not always better, especially for sensitive skin. If uneven tone is your main concern, combine vitamin C with daily SPF and patience. A skin scan can help you see whether your tone is evening out over time. Try the scan.