Which form of vitamin C is best in a serum?

L-ascorbic acid has the most research behind it, which is why SkinCeuticals C E Ferulic and The Ordinary’s 23% suspension use it. Derivatives such as tetrahexyldecyl ascorbate (Medik8 C-Tetra) and 3-O-ethyl ascorbic acid (Beauty of Joseon Light On) are more stable but less extensively studied.

Should vitamin C serum go on in the morning or evening?

Most brands direct it for mornings, under sunscreen. The Ordinary is the exception: it directs its 23% suspension for once-daily use, ideally in the evening. Follow the directions for the exact product.

Is it normal for vitamin C serum to change colour?

L-ascorbic acid oxidises over time and can turn yellow or amber. Keep the cap closed, store it as the brand directs and check the brand’s guidance; derivatives are more resistant to this.

Can I use vitamin C with retinol?

Keep them apart. The Ordinary advises against combining its 23% suspension with retinoids, so a common approach is vitamin C in the morning and a retinoid at night.

Does vitamin C replace sunscreen?

No. Vitamin C is an antioxidant step, not UV protection. Every brand in this guide pairs its serum with sunscreen during the day.

Best of · Skin prep · 4 picks

The best vitamin C serums.

Pure L-ascorbic acid or a more stable derivative? Four serums compared by the form of vitamin C, its stated strength, texture, directions and UK price.

By Kaiser Khan, Founder & Editor Updated 25 September 2026 Editorial policy

Quick answer

What is the best vitamin C serum in the UK?

SkinCeuticals C E Ferulic is the benchmark: 15% L-ascorbic acid with vitamin E and ferulic acid for morning use, at £169. The Ordinary’s 23% suspension offers L-ascorbic acid for £7.70, with a tingling warning and evening directions. Medik8 C-Tetra and Beauty of Joseon Light On use more stable derivatives, at £45 and £14.50.

Selection is editorial and never paid for. Prices are UK guide prices from official pages or named retailers when checked, and may have changed. How we chose.

Our top picks

The shortlist, by what each does best.

Best overall C E Ferulic SkinCeuticals · 15% L-ascorbic acid · 1% vitamin E · 0.5% ferulic
Best budget Vitamin C Suspension 23% + HA Spheres 2% The Ordinary · 23% L-ascorbic acid · water-free · £7.70
Best oil-based serum C-Tetra Medik8 · 7% tetrahexyldecyl ascorbate · lightweight oil
Best K-beauty pick Light On Serum: Centella + Vita C Beauty of Joseon · 3-O-ethyl ascorbic acid · centella · fragrance-free

Side by side

How the picks compare.

Specifications are summarised from each official product page. Read across a row to see where a product fits; the detailed notes below explain the trade-offs.

Best vitamin C serums: how the picks compare
Product	Award	Finish	Key spec	Guide price
C E FerulicSkinCeuticals · Antioxidant serum	Best overall	Light, silky	15% L-ascorbic acid · 1% vitamin E · 0.5% ferulic	£169
Vitamin C Suspension 23% + HA Spheres 2%The Ordinary · Water-free vitamin C suspension	Best budget	Slightly granular	23% L-ascorbic acid · water-free · £7.70	£7.70
C-TetraMedik8 · Vitamin C oil serum	Best oil-based serum	Lightweight oil	7% tetrahexyldecyl ascorbate · lightweight oil	£45
Light On Serum: Centella + Vita CBeauty of Joseon · Vitamin C serum	Best K-beauty pick	Lightweight, non-sticky	3-O-ethyl ascorbic acid · centella · fragrance-free	£14.50

Specifications from official brand pages; prices are UK guide prices from the brand’s official page or a named UK retailer, checked 25 September 2026. Prices and formulas can change.

The picks in detail

Why each one earns its place.

Strengths and limitations are drawn from specifications — texture, finish, shade range, filters, fragrance, price and availability — not from wear testing.

Best overall

C E Ferulic

SkinCeuticals

SkinCeuticals combines the most studied form of vitamin C, L-ascorbic acid, at 15% with 1% vitamin E and 0.5% ferulic acid, and states all three strengths. The directions are simple: four to five drops each morning, followed by moisturiser and broad-spectrum sunscreen.

Format: Antioxidant serum
Finish: Light, silky
Key spec: 15% L-ascorbic acid · 1% vitamin E · 0.5% ferulic

What stands out

Pure L-ascorbic acid, the form with the deepest research base
Stated percentages for all three antioxidants
Listed as fragrance-free by Space NK
Morning directions that fit a sunscreen routine

Consider first

£169 for 30ml — by far the most expensive pick
L-ascorbic acid oxidises, which can darken the serum over time
A reformulated US version was announced in July 2026, so check which formula your retailer supplies

Read the full product guide SkinCeuticals official page Guide price: £169

Best budget

Vitamin C Suspension 23% + HA Spheres 2%

The Ordinary

The Ordinary suspends a high 23% concentration of L-ascorbic acid in a water-free base with hyaluronic acid spheres, at a fraction of the price of the other picks. The brand states the trade-offs itself: a slightly granular texture, expected tingling and once-daily use, ideally in the evening.

Format: Water-free vitamin C suspension
Finish: Slightly granular
Key spec: 23% L-ascorbic acid · water-free · £7.70

What stands out

£7.70 for 30ml
L-ascorbic acid rather than a derivative
Vegan, alcohol-free and silicone-free, per the brand
Water-free base, which helps keep L-ascorbic acid stable

Consider first

The brand warns of tingling and describes a slightly granular texture
Directed for evening use, so it is not a morning antioxidant step
Not to be combined with niacinamide, retinoids, peptides or direct acids, per the brand

Read the full product guide The Ordinary official page Guide price: £7.70

Best oil-based serum

C-Tetra

Medik8

C-Tetra uses tetrahexyldecyl ascorbate, an oil-soluble vitamin C derivative, at 7% in a lightweight, water-free oil with vitamin E. Derivatives like this are more stable than L-ascorbic acid, though less extensively studied; Medik8 directs four drops each morning before sunscreen.

Format: Vitamin C oil serum
Finish: Lightweight oil
Key spec: 7% tetrahexyldecyl ascorbate · lightweight oil

What stands out

Stated 7% concentration of a stable derivative
Water-free oil texture with vitamin E
Morning directions that pair naturally with sunscreen
An 8ml travel size (£15) to try the texture first

Consider first

Contains grapefruit peel oil and fragrance allergens such as limonene and citral, despite “no artificial fragrance” wording
A derivative, with less clinical evidence than L-ascorbic acid
£45 for 30ml

Read the full product guide Medik8 official page Guide price: £45

Best K-beauty pick

Light On Serum: Centella + Vita C

Beauty of Joseon

Beauty of Joseon pairs 3-O-ethyl ascorbic acid, a stabilised vitamin C derivative, with centella asiatica, panthenol and vitamin E in a fragrance-free serum. It is directed for morning and evening use, with sunscreen by day, for £14.50.

Format: Vitamin C serum
Finish: Lightweight, non-sticky
Key spec: 3-O-ethyl ascorbic acid · centella · fragrance-free

What stands out

Labelled fragrance-free
£14.50 for 30ml on the brand’s UK-priced store
Morning and evening directions
Lightweight, non-sticky texture, per the brand

Consider first

The brand does not state the vitamin C concentration
A derivative rather than L-ascorbic acid
The brand advises a patch test and no layering with AHA, BHA or PHA exfoliants

Read the full product guide Beauty of Joseon official page Guide price: £14.50

What to look for

Read the label before the award.

The form of vitamin C

L-ascorbic acid is the most studied form but is unstable in water and oxidises. Derivatives such as tetrahexyldecyl ascorbate and 3-O-ethyl ascorbic acid are more stable, but there is less published evidence on how much becomes active vitamin C in skin.

A stated strength

Look for a percentage. Research summarised by Telang (2013) found the benefit of L-ascorbic acid rises with concentration only up to about 20%, so a higher number is not automatically better.

Packaging and colour

Oxidised L-ascorbic acid turns yellow to amber. Keep the cap closed, store the bottle as the brand directs and follow its guidance on colour change.

Morning or evening

Most brands direct vitamin C for the morning, under sunscreen. The Ordinary’s 23% suspension is the exception, directed for evenings. Vitamin C never replaces SPF.

Fragrance and tingling

Read past “no artificial fragrance” to the ingredient list: essential oils can still add fragrance allergens. Low-pH L-ascorbic acid serums can tingle, and the brands say so.

What not to mix

Brands list their own conflicts. The Ordinary advises against pairing its suspension with niacinamide or retinoids, and Beauty of Joseon against layering Light On with exfoliating acids.

How we chose

Desk research, stated plainly.

This guide is desk research. We compared vitamin C serums sold in the UK using the brands’ published formulas, ingredient lists, specifications and directions, together with UK prices from official pages or named retailers on 25 September 2026. None of the products was tested in a laboratory or worn by our editors for this guide.

We recorded the form of vitamin C, its stated concentration, supporting antioxidants, fragrance, directions and UK price, and we noted where a brand does not publish its strength.

Awards describe fit — the job a product is best suited to — rather than a single overall score. Brand claims are reported as brand claims. No brand paid for inclusion, and shopping links elsewhere on the site do not influence which products appear here.

Questions

Best vitamin C serums, answered

Which form of vitamin C is best in a serum?: L-ascorbic acid has the most research behind it, which is why SkinCeuticals C E Ferulic and The Ordinary’s 23% suspension use it. Derivatives such as tetrahexyldecyl ascorbate (Medik8 C-Tetra) and 3-O-ethyl ascorbic acid (Beauty of Joseon Light On) are more stable but less extensively studied.
Should vitamin C serum go on in the morning or evening?: Most brands direct it for mornings, under sunscreen. The Ordinary is the exception: it directs its 23% suspension for once-daily use, ideally in the evening. Follow the directions for the exact product.
Is it normal for vitamin C serum to change colour?: L-ascorbic acid oxidises over time and can turn yellow or amber. Keep the cap closed, store it as the brand directs and check the brand’s guidance; derivatives are more resistant to this.
Can I use vitamin C with retinol?: Keep them apart. The Ordinary advises against combining its 23% suspension with retinoids, so a common approach is vitamin C in the morning and a retinoid at night.
Does vitamin C replace sunscreen?: No. Vitamin C is an antioxidant step, not UV protection. Every brand in this guide pairs its serum with sunscreen during the day.

Sources

Where the facts come from.

All sources checked 25 September 2026. Spotted an error? Email desk@thecastindex.com or read our corrections policy.

Head to head

Deciding between two?

Side-by-side comparisons of products in this guide, with a specification table and a “choose this if” verdict.

SkinCeuticals vs Medik8 C E Ferulic vs C-Tetra

Keep exploring

What is the best vitamin C serum in the UK?

The shortlist, by what each does best.

How the picks compare.

Why each one earns its place.

C E Ferulic

What stands out

Consider first

Vitamin C Suspension 23% + HA Spheres 2%

What stands out

Consider first

C-Tetra

What stands out

Consider first

Light On Serum: Centella + Vita C

What stands out

Consider first

Read the label before the award.

The form of vitamin C

A stated strength

Packaging and colour

Morning or evening

Fragrance and tingling

What not to mix

Desk research, stated plainly.

Best vitamin C serums, answered

Which form of vitamin C is best in a serum?

Should vitamin C serum go on in the morning or evening?

Is it normal for vitamin C serum to change colour?

Can I use vitamin C with retinol?

Does vitamin C replace sunscreen?

Where the facts come from.

Deciding between two?

More best-of guides.