Vitamin C Serum: How to Choose and Use It

A vitamin C serum is an antioxidant step for the morning. Choose it by two things: the form of vitamin C on the label, and the bottle it comes in. Pure ascorbic acid is the most studied form and the most delicate; the stabilised forms are gentler and keep longer. Use a few drops on clean skin, before moisturiser and always before sunscreen. If the serum turns a deep orange or brown, it has oxidised, and it is time for a fresh one.

What Does Vitamin C Do for Skin?

Vitamin C is an antioxidant. In skincare, that means it helps neutralise free radicals, the unstable molecules that sunlight and pollution create at the surface of the skin and that contribute to a dull, tired look over time. Used every day, a well-made vitamin C serum supports a brighter-looking, more even complexion.

It works alongside sunscreen, not in place of it. Vitamin C does not filter UV light, which is why the two belong together in the morning, with sunscreen always the final step.

Which Form of Vitamin C Is on the Label?

Vitamin C appears on an ingredient list under several names. They are related, but they behave differently in the bottle and on the skin.

• Ascorbic acid, sometimes written L-ascorbic acid: the pure form and the most studied. It is also the least stable, and some skins feel a brief tingle when they first use it.
• Ascorbyl glucoside: vitamin C bound to a sugar molecule, which makes it far more stable. A gentle, steady choice.
• 3-O-ethyl ascorbic acid, often shortened to ethyl ascorbic acid: a stabilised form that works in creams as well as serums.
• Sodium ascorbyl phosphate: a salt of vitamin C, stable and generally well tolerated.
• Tetrahexyldecyl ascorbate, or THD ascorbate (also listed as ascorbyl tetraisopalmitate): an oil-soluble form, very stable, suited to oil-based serums and capsules.

If your skin is resilient and you want the classic form, choose ascorbic acid. If your skin is sensitive, or vitamin C is new to you, start with one of the stabilised forms.

Vitamin C Serums Built Around Ascorbic Acid

These four serums are built on pure ascorbic acid, each in its own way. La Roche-Posay's Pure Vitamin C12 pairs it with hyaluronic acid and salicylic acid, and is meant for the morning, followed by moisturiser and SPF. Institut Esthederm's Intensive Vitamine C² Double Concentré combines 10% ascorbic acid with 2% ascorbyl glucoside in dual-chamber packaging. The Pure Vitamin C Radiance Concentrate from Clarins pairs 10% L-ascorbic acid with 5% ascorbyl glucoside as a measured seven-day course. Revox B77's Just Vitamin C 20% is the most direct of the four: 20% ascorbic acid with aloe vera and green tea extract, in an amber dropper bottle.

• Pure Vitamin C12 Face Serum
• Intensive Vitamine C² Double Concentré Face Serum
• Pure Vitamin C Radiance Concentrate 8 ml
• Just Vitamin C 20% Antioxidant Face Serum

Stabilised Vitamin C Serums

A stabilised form asks less of you and of your skin. The iDSkin Identity serum from Skin Generics is built on 3% ascorbyl glucoside in a lightweight texture. Endocare's Radiance C Ferulic Edafence Face Serum pairs sodium ascorbyl phosphate with ferulic acid, and suits morning or evening. Elizabeth Arden's Vitamin C Ceramide Capsules hold THD ascorbate and ceramides in an oil base, one sealed dose at a time. Payot's My Sérum Vitamine C Éclat uses ethyl ascorbic acid with superfruits, in a pump bottle that layers neatly under cream.

• iDSkin Identity Ascorbyl Glucoside 3% Stabilised Vitamin C Antiox Serum Face Serum
• Radiance C Ferulic Edafence Face Serum
• Vitamin C Ceramide Capsules Radiance Renewal Serum
• My Sérum Vitamine C Éclat Face Serum

Why Does Packaging Matter?

Light and air are what break vitamin C down, and pure ascorbic acid is the most sensitive to both. That is why good vitamin C serums tend to come in amber or opaque glass, with a dropper or pump that lets in as little air as possible. Some go further. Institut Esthederm keeps its concentrate in dual-chamber packaging; Elizabeth Arden seals each dose in its own capsule; Clarins measures out a single week's course, so there is never an old bottle to finish.

At home, keep the cap closed and the bottle out of sunlight, in a cupboard rather than on a bright windowsill. Use it within the period shown on the pack by the small open-jar symbol, and buy a size you will finish.

How to Tell If Vitamin C Has Oxidised

Watch the colour. A fresh ascorbic acid serum is usually clear or a pale straw shade. As it oxidises it deepens to yellow, then orange, then brown. Some serums are tinted from the start, so compare the colour with how it looked on the day you opened it rather than with a rule. A noticeably darker shade, or a change in scent, means the serum is past its best and should be replaced.

How to Use Vitamin C in the Morning

1. Cleanse and pat the skin dry.
2. Apply a few drops of serum to the face and neck, avoiding the eye area unless the product is made for it. Give it a minute to settle.
3. Follow with your moisturiser.
4. Finish with a generous layer of sunscreen, as the last step.

Patch test a new serum first, on a small area such as the inner arm, for a day or two. A light tingle in the first week with ascorbic acid is common; redness or stinging that lasts means stop. If your skin is sensitive, begin every other morning and build up.

For how a vitamin C serum fits into a full summer morning, from the face to the body after the shower, read our summer vitamin C ritual.

Vitamin C in a Cream, an Emulsion or an Eye Cream

A serum is not the only way to wear vitamin C. Avène's Vitamin Activ Cg Intensive Radiance Cream pairs 1.8% Vitamin Cg, built on ascorbyl glucoside, with 6% niacinamide and hyaluronic acid. The Brightening Vitamin C Hydrating Emulsion from Clarins is lighter, combining ascorbyl glucoside with acerola and sambucus extracts. Natura Bissé's C+C Vitamin Eye brings stabilised vitamin C, vitamin E, ginseng and caffeine to a cooling gel-cream for the eye area, tapped in with the fingertips. Collistar's Vitamin C + Ferulic Acid Cream pairs ethyl ascorbic acid with ferulic acid in a light, fast-absorbing texture.

• Vitamin Activ Cg Intensive Radiance Cream
• Brightening Vitamin C Hydrating Emulsion
• C+C Vitamin Eye Eye Cream
• Vitamin C + Ferulic Acid Cream

What Pairs Well With Vitamin C?

• Vitamin E and ferulic acid: fellow antioxidants and the classic companions to vitamin C.
• Hyaluronic acid: adds hydration without weight, and sits easily in the same routine.
• Niacinamide: once thought to clash with vitamin C, it now appears beside it in many formulas.
• Retinol: keep it for the evening and vitamin C for the morning. Start retinol slowly, and wear sunscreen by day. If you are pregnant or breastfeeding, ask your pharmacist or doctor before using it.
• Exfoliating acids (AHAs and BHAs): pure vitamin C is itself acidic, so layering it with a strong exfoliant can be too much. Use them at different times of day or on different days, and patch test.

Where to Begin

If this is your first vitamin C serum, choose a stabilised form in a dark or sealed bottle, use it every morning for a month under your sunscreen, and judge it by how your skin looks in daylight.