# 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.

- Canonical: https://thecastindex.com/beauty/best/best-vitamin-c-serums
- Author: Kaiser Khan (Founder & Editor)
- Published: 2026-09-25
- Updated: 2026-09-25
- Category guide: https://thecastindex.com/beauty/category/skin-prep
- Method: desk research from published formulas, specifications and brand/retailer information — not lab or hands-on tested

## 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.

## Our top picks

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

## Side by side

| Product | Award | Finish | Key spec | Guide price |
| --- | --- | --- | --- | --- |
| [SkinCeuticals C E Ferulic](https://thecastindex.com/beauty/skinceuticals-c-e-ferulic) | Best overall | Light, silky | 15% L-ascorbic acid · 1% vitamin E · 0.5% ferulic | £169 |
| [The Ordinary Vitamin C Suspension 23% + HA Spheres 2%](https://thecastindex.com/beauty/the-ordinary-vitamin-c-suspension-23-ha-spheres-2) | Best budget | Slightly granular | 23% L-ascorbic acid · water-free · £7.70 | £7.70 |
| [Medik8 C-Tetra](https://thecastindex.com/beauty/medik8-c-tetra) | Best oil-based serum | Lightweight oil | 7% tetrahexyldecyl ascorbate · lightweight oil | £45 |
| [Beauty of Joseon Light On Serum: Centella + Vita C](https://thecastindex.com/beauty/beauty-of-joseon-light-on-serum-centella-vita-c) | Best K-beauty pick | Lightweight, non-sticky | 3-O-ethyl ascorbic acid · centella · fragrance-free | £14.50 |

Prices are UK guide prices from the brand’s official page or a named UK retailer, checked 2026-09-25; they may have changed.

## The picks in detail

### 1. Best overall: SkinCeuticals C E Ferulic

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.

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

Product guide: https://thecastindex.com/beauty/skinceuticals-c-e-ferulic
Official page: https://www.skinceuticals.co.uk/en_GB/c-e-ferulic-antioxidant-serum/635494363210.html

### 2. Best budget: The Ordinary Vitamin C Suspension 23% + HA Spheres 2%

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.

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

Product guide: https://thecastindex.com/beauty/the-ordinary-vitamin-c-suspension-23-ha-spheres-2
Official page: https://theordinary.com/en-gb/vitamin-c-suspension-23-ha-spheres-2-vitamin-c-100451.html

### 3. Best oil-based serum: Medik8 C-Tetra

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.

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

Product guide: https://thecastindex.com/beauty/medik8-c-tetra
Official page: https://www.medik8.com/products/c-tetra

### 4. Best K-beauty pick: Beauty of Joseon Light On Serum: Centella + Vita C

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.

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

Product guide: https://thecastindex.com/beauty/beauty-of-joseon-light-on-serum-centella-vita-c
Official page: https://beautyofjoseon.com/products/light-on-serum-centella-vita-c

## What to look for

### 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

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

### 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

- [Pullar JM, Carr AC, Vissers MCM (2017) — The Roles of Vitamin C in Skin Health, Nutrients](https://pmc.ncbi.nlm.nih.gov/articles/PMC5579659/)
- [Telang PS (2013) — Vitamin C in dermatology, Indian Dermatology Online Journal](https://pmc.ncbi.nlm.nih.gov/articles/PMC3673383/)
- [Al-Niaimi F, Chiang NYZ (2017) — Topical Vitamin C and the Skin, Journal of Clinical and Aesthetic Dermatology](https://pmc.ncbi.nlm.nih.gov/articles/PMC5605218/)
- [The Ordinary UK — vitamin C range](https://theordinary.com/en-gb/category/skincare/shop-by-ingredients/vitamin-c)
- [LOOKFANTASTIC — SkinCeuticals C E Ferulic 30ml](https://www.lookfantastic.com/p/skinceuticals-c-e-ferulic-antioxidant-vitamin-c-serum-for-normal-and-dry-skin-30ml/11705727/)
- [Space NK — SkinCeuticals C E Ferulic](https://www.spacenk.com/uk/skincare/treatment/serums/c-e-ferulic-MUK200066059.html)
- [SkinCeuticals C E Ferulic — official product page](https://www.skinceuticals.co.uk/en_GB/c-e-ferulic-antioxidant-serum/635494363210.html)
- [The Ordinary Vitamin C Suspension 23% + HA Spheres 2% — official product page](https://theordinary.com/en-gb/vitamin-c-suspension-23-ha-spheres-2-vitamin-c-100451.html)
- [Medik8 C-Tetra — official product page](https://www.medik8.com/products/c-tetra)
- [Beauty of Joseon Light On Serum: Centella + Vita C — official product page](https://beautyofjoseon.com/products/light-on-serum-centella-vita-c)

## Head-to-head comparisons

- [C E Ferulic vs C-Tetra](https://thecastindex.com/beauty/vs/skinceuticals-c-e-ferulic-vs-medik8-c-tetra)