A vitamin C serum is a lightweight skincare product that delivers vitamin C, an antioxidant, directly to the skin. Its best-studied form, L-ascorbic acid, works mainly by helping to neutralise free radicals from sunlight and pollution, and it also plays a role in collagen formation and in reducing the formation of pigment. To get any benefit, the serum needs a suitable form and concentration, stable packaging, and a daily sunscreen on top, because vitamin C does not replace SPF.
This explainer covers how vitamin C works in skin, the different forms you will see on labels, what concentration makes sense, how to fit a serum into a morning routine with SPF, and what to do if your skin does not like it.
In short
- L-ascorbic acid is the most studied form of vitamin C in skincare, but it is unstable and needs a low pH to reach the skin.
- A review in the Journal of Clinical and Aesthetic Dermatology describes 10 to 20 percent as the usual range, with no extra benefit shown above 20 percent.
- Derivatives such as ascorbyl glucoside, magnesium ascorbyl phosphate and tetrahexyldecyl ascorbate are more stable and often gentler, but have less clinical evidence.
- Vitamin C works well alongside vitamin E and ferulic acid, and it should always be followed by sunscreen during the day.
- A serum that has turned dark orange or brown has oxidised and is unlikely to work as intended.
How does vitamin C work on the skin?
Vitamin C is an antioxidant, which means it can neutralise unstable molecules called free radicals. Ultraviolet light, air pollution and cigarette smoke create free radicals in the skin, and over time they contribute to visible signs of ageing such as fine lines, uneven tone and a duller look. Our article on how skin ages explains that process in more detail.
Vitamin C has two further roles. It is a cofactor for the enzymes that stabilise collagen, the protein that gives skin its structure, and it inhibits tyrosinase, the enzyme that drives the production of the pigment melanin. A review by Al-Niaimi and Chiang in the Journal of Clinical and Aesthetic Dermatology (2017) summarises these effects and notes that topical vitamin C has an excellent safety profile, although clinical studies are mostly small.
The body cannot make vitamin C, so it comes from food. Eating enough fruit and vegetables matters for your health in general, but very little of the vitamin C you eat ends up in the outer layers of the skin, which is why skincare products apply it directly. Our guide to how much vitamin C you need each day covers the dietary side.
Which form of vitamin C works best in a serum?
Vitamin C appears on labels under several names. They differ in stability, how easily they get into the skin and how much evidence supports them. The table summarises the most common forms.
| Form on the label | Stability | Skin feel | Evidence |
|---|---|---|---|
| Ascorbic Acid (L-ascorbic acid) | Low; oxidises in air, light and heat | Can tingle or sting, especially on sensitive skin | The most studied form for sun-related ageing |
| Ascorbyl Glucoside | Good | Usually gentle | Some studies on uneven pigmentation |
| Magnesium Ascorbyl Phosphate or Sodium Ascorbyl Phosphate | Good at neutral pH | Gentle | Limited clinical data |
| Ascorbyl Palmitate | Good, oil-soluble | Gentle | Limited clinical data |
| Tetrahexyldecyl Ascorbate | Good, oil-soluble | Often suggested for sensitive skin | Growing but still limited |
Al-Niaimi and Chiang point out a catch with derivatives: one study found that daily use of several of them did not raise L-ascorbic acid levels in the skin. A 2026 systematic review by Boghosian and colleagues in the same journal reached a similar overall conclusion, saying that the effect depends on the chemistry of the derivative, the pH, the base formula and how the product is stabilised, rather than on the vitamin C content alone.
What concentration of vitamin C should you look for?
More is not always better. According to Al-Niaimi and Chiang, concentrations above 8 percent are considered biologically meaningful, extra benefit has not been shown above 20 percent, and irritation becomes more likely at higher strengths. Most L-ascorbic acid serums therefore sit between 10 and 20 percent. To get into the skin, L-ascorbic acid also needs an acidic pH below 3.5, which is one reason it can tingle.
If you are new to vitamin C or have sensitive skin, starting with a lower strength of around 10 percent, or with a gentler derivative, is sensible. You can move to a stronger product later if your skin is comfortable.
How do you use a vitamin C serum with SPF?
Most people use vitamin C in the morning, because its antioxidant role is most useful during the hours you spend in daylight. A simple order works well:
- Cleanse your face gently and pat it dry.
- Apply three or four drops of vitamin C serum to the face and neck and let it absorb for a minute.
- Apply your usual moisturiser.
- Finish with a broad-spectrum sunscreen of at least SPF 30 on all exposed skin.
The final step is not optional. Al-Niaimi and Chiang describe vitamin C as reducing some of the damage caused by ultraviolet light in laboratory studies, but it is not a sunscreen and does not replace one. The combination is what makes sense: sunscreen reduces the amount of UV reaching the skin, and vitamin C helps with some of the free radicals that still form.
Many serums combine vitamin C with vitamin E and ferulic acid. Both reviews describe this pairing positively, because vitamin E and vitamin C support each other and ferulic acid helps stabilise the formula.
How do you keep a vitamin C serum from going off?
L-ascorbic acid oxidises when it meets air, light and warmth. Fresh serums are usually clear or pale yellow; a serum that has turned dark orange or brown has oxidised and is unlikely to work as intended. To make a bottle last:
- choose dark glass, an airless pump or an opaque tube rather than a clear bottle;
- close the cap straight after use and keep the product away from a sunny windowsill or a steamy bathroom shelf;
- buy a size you will finish within two to three months.
Who should be careful with vitamin C serums?
Low-pH vitamin C can sting, especially on sensitive skin, around the nose and on skin that is already irritated. The 2026 review notes that this is why gentler derivatives are often suggested for sensitive skin. Avoid applying a strong vitamin C serum straight after shaving, exfoliating or a peel, and introduce it slowly, every second day at first.
Patch test any new serum on a small area along the jawline for a few days. Stop using it if you notice burning, persistent redness, swelling or a rash. If irritation does not settle within a few days of stopping, or if you have a skin condition such as rosacea, ask a pharmacist or GP before trying again. People who are already using prescription creams should check with the prescriber first.
Do we offer a vitamin C serum?
No. The LR range available in the UK does not currently include a vitamin C serum, so this article is purely an ingredient explainer. If you are building a wider routine for ageing skin, our guide to what an anti-wrinkle cream can realistically do looks at moisturisers and other everyday steps.
Frequently asked questions
Can I use vitamin C serum at night?
Yes, you can, but most people prefer the morning so that its antioxidant role coincides with daylight. If you use a retinoid at night, keep vitamin C for the morning to reduce the risk of irritation.
Can I use vitamin C with niacinamide?
Many people use both without problems, either layered or at different times of day. If your skin becomes red or flushed, separate them, for example vitamin C in the morning and niacinamide in the evening.
How long until I see results?
Studies usually run for several weeks to a few months. Expect gradual changes in brightness and evenness rather than quick results, and keep using sunscreen throughout.
Is vitamin C serum suitable for darker skin?
Yes, and some people use it specifically for uneven pigmentation. The 2026 review notes that studies have included relatively few people with darker skin, so patch testing and a gentle start are especially worthwhile.
Sources
- Al-Niaimi F, Chiang NYZ. Topical Vitamin C and the Skin: Mechanisms of Action and Clinical Applications. J Clin Aesthet Dermatol. 2017
- Boghosian T et al. Clinical Applications of Vitamin C in Dermatology: A Systematic Review. J Clin Aesthet Dermatol. 2026
We are independent LR partners and do not speak for LR Health & Beauty.