A vitamin C serum is a light skincare product that contains vitamin C, usually alongside water, glycerin and other ingredients. The serums on the market differ in three main ways: which form of vitamin C they use, how much of it they contain, and how well the packaging protects it from air and light.
Pure vitamin C, listed as ascorbic acid or L-ascorbic acid, breaks down quickly once it meets air, light and warmth. That is why brands use dark or airless bottles, and why many serums use more stable vitamin C derivatives instead. A serum that has turned dark orange or brown has oxidised and is past its best.
Skincare is personal, and a product that suits one person may irritate another. If you have a skin condition such as eczema, rosacea or acne, or a reaction that does not settle, speak to a pharmacist, your GP or a dermatologist before trying new products.
Forms of vitamin C on the label
The ingredients list (INCI) tells you which form a serum uses:
| INCI name | Common name | Notes |
|---|---|---|
| Ascorbic acid | L-ascorbic acid | The pure form; least stable, often in low pH formulas that can tingle |
| Sodium ascorbyl phosphate | SAP | Water soluble derivative, more stable |
| Magnesium ascorbyl phosphate | MAP | Water soluble derivative, gentle and stable |
| Ascorbyl glucoside | Water soluble derivative, common in lighter serums | |
| Tetrahexyldecyl ascorbate | THD ascorbate | Oil soluble derivative, often in oil based serums |
| 3-O-ethyl ascorbic acid | Ethyl ascorbic acid | Derivative used in many newer formulas |
Derivatives are more stable on the shelf, while ascorbic acid is the form most often discussed in skincare research. Neither is automatically better: stability, texture and how your skin tolerates the product matter as much as the form.
What the percentage means
Many brands state a percentage, often somewhere between 5 and 20 percent. A higher number is not always better. Stronger ascorbic acid serums are more likely to sting, especially on sensitive skin, and the percentage of a derivative cannot be compared directly with the percentage of pure ascorbic acid. Some brands do not state a percentage at all; in that case, the position of vitamin C in the ingredients list gives a rough idea, since ingredients are listed in descending order of concentration down to 1 percent.
If you are new to vitamin C, a lower strength or a derivative is a sensible place to start. You can compare options in the serums range, which also includes eye serums with vitamin C for the thinner skin around the eyes.
Packaging and storage
Because vitamin C breaks down, packaging is one of the most useful things to check:
- Opaque or dark glass protects the serum from light.
- Airless pumps limit contact with air better than dropper bottles.
- Small bottles are used up before they have time to oxidise.
- Period after opening (PAO) is shown by an open jar symbol with a number of months, such as 6M or 12M.
Keep the bottle closed, away from sunlight and away from heat such as a sunny windowsill or a steamy bathroom shelf. Some people keep vitamin C serums in a cool cupboard for this reason. Throw the serum away if the colour or smell changes noticeably.
How to fit it into a routine
Most vitamin C serums are applied after cleansing and before moisturiser:
- Cleanse and pat the skin dry.
- Apply a few drops of serum and let it absorb.
- Follow with a moisturiser from the face creams range.
- In the morning, finish with a broad spectrum sunscreen.
Vitamin C is not a sunscreen and does not replace one. The NHS advises using a sunscreen with at least SPF 30 and at least four star UVA protection when you are in the sun. Many day creams in the age care section include SPF, which can simplify a morning routine.
Some people use vitamin C and other active ingredients, such as retinol or exfoliating acids, at different times of day to reduce the chance of irritation. Follow the instructions on each product.
Patch testing
Patch test any new skincare product. Apply a small amount to a discreet area, such as behind the ear or on the inner arm, and wait 24 to 48 hours. A little tingling with ascorbic acid serums is common, but stop using the product if you get redness, itching, swelling or a rash. If symptoms are severe or do not go away, contact a pharmacist or GP.
Other vitamin C products
Vitamin C also appears in masks, creams and eye treatments. A vitamin C mask, such as those in the face masks range, is used once or twice a week rather than daily. Taking vitamin C as a supplement is a separate topic: the NHS says most adults need 40 mg a day and can get it from food, and that very high doses can upset the stomach. For vitamins you take by mouth, the guide to vitamin D supplements explains how to read doses on the label.
Quick checklist
- Form of vitamin C in the ingredients list: ascorbic acid or a derivative.
- Strength that suits your skin; start lower if you are new to it.
- Dark or airless packaging and a sensible bottle size.
- Check the period after opening and store away from heat and light.
- Apply before moisturiser and always use sunscreen in the day.
- Patch test first and stop if irritation develops.
- Ask a pharmacist or GP about any skin condition.
Common questions
Why has my vitamin C serum turned orange?
It has oxidised after contact with air, light or heat. A slight change can be normal over time, but a dark orange or brown serum is past its best and is best replaced.
Can I use vitamin C serum every day?
Many people do, but it depends on the product and your skin. Follow the instructions and use it less often if your skin feels irritated.
Do I still need sunscreen if I use vitamin C?
Yes. Vitamin C serum does not protect against UV, so use a broad spectrum sunscreen of at least SPF 30 during the day.
