A vitamin C serum is one of the most popular morning skincare products. Vitamin C is an antioxidant: it helps to defend the skin against damage from sunlight and pollution, it can brighten uneven tone, and it supports collagen. It is also an awkward ingredient. It breaks down easily, and products vary a great deal. Knowing what to look for saves money and disappointment.
How this guide was put together
The guidance here rests on what is known about the different forms of vitamin C, on typical ingredient lists and packaging, and on dermatology advice. It is not a hands-on test of particular serums, and it names no brands.
Forms of vitamin C
| Name on the label | Notes |
|---|---|
| Ascorbic acid, or L-ascorbic acid | The pure, most studied form; effective, but unstable and can sting |
| Sodium ascorbyl phosphate | More stable; gentler; often used for acne-prone skin |
| Magnesium ascorbyl phosphate | Stable; gentle; suits dry or sensitive skin |
| Ascorbyl glucoside | Stable; mild; brightening |
| 3-O-ethyl ascorbic acid | Stable; newer; promising |
| Tetrahexyldecyl ascorbate, or ascorbyl tetraisopalmitate | Oil-soluble; stable; found in richer formulas |
| Ascorbyl palmitate | Stable; weaker evidence |
The derivatives have to be converted to ascorbic acid in the skin. They are gentler and last longer in the bottle, but there is less research behind them than behind pure ascorbic acid.
Strength
- For L-ascorbic acid, studies mostly support strengths of about 10% to 20%. Above 20% tends to add irritation without clear extra benefit.
- Beginners and sensitive skin can start at 5% to 10%, or with a derivative.
- For derivatives, percentages are not directly comparable with ascorbic acid.
Supporting ingredients
- Vitamin E (tocopherol) and ferulic acid help to stabilize ascorbic acid, and may improve its protective effect.
- Hyaluronic acid or glycerin add hydration.
- Niacinamide can be used with vitamin C. See Niacinamide Serum Buying Guide: What to Look For.
Why packaging matters
Ascorbic acid reacts with air, light and heat. Once it oxidizes, it no longer works, and it may irritate.
| Packaging | How well it protects |
|---|---|
| Opaque, airless pump | Best |
| Dark or opaque glass with a dropper | Good, though air enters each time it is opened |
| Clear glass or plastic | Poor, unless the formula uses a stable derivative |
| Single-use capsules or powders mixed before use | Very good |
Smaller bottles make sense. You will finish them before they spoil.
How to spot oxidation
A fresh ascorbic acid serum is clear to pale straw-colored. As it oxidizes, it turns yellow, then orange, then brown. A dark orange or brown serum, or one with a changed smell, should be replaced.
Texture and skin type
| Skin type | A sensible choice |
|---|---|
| Oily or acne-prone | Lightweight, water-based serum; sodium ascorbyl phosphate is an option |
| Dry or mature | Serum with hydrating ingredients, or an oil-soluble derivative |
| Sensitive | A gentle derivative at a low strength; fragrance-free |
| Normal or combination | L-ascorbic acid at 10% to 15%, if tolerated |
How to use it
- Cleanse in the morning.
- Apply a few drops to dry skin on the face and neck.
- Let it settle for a minute.
- Apply moisturizer.
- Apply sunscreen. Vitamin C supports sun protection. It does not replace it.
See Morning Skincare Routine: A Simple Step-by-Step Guide and How to Layer Serums and Moisturizers.
What to expect
- A brief tingle is common with ascorbic acid. Persistent stinging or redness means that the product is too strong for you.
- A brighter, more even look usually takes 8 to 12 weeks of daily use.
- Dark marks fade slowly. See Acne Scars vs Dark Spots: How to Tell the Difference.
Storage
- Close the cap tightly, straight after use.
- Keep it in a cool, dark place. A fridge is fine, though not essential.
- Note the date you opened it, and aim to finish it within about three months, or as the label advises.
Label claims to treat with care
- "Stabilized" is helpful, but it is not a guarantee.
- "Clinical strength" has no fixed meaning.
- Before-and-after photos depend heavily on lighting.
- A high price does not prove a better formula.
You can check individual ingredient names in the Skincare Ingredient Checker.
Related on ArniSun
- Niacinamide Serum Buying Guide: What to Look For
- How to Layer Serums and Moisturizers
- Acne Scars vs Dark Spots: How to Tell the Difference
- Morning Skincare Routine: A Simple Step-by-Step Guide
- Skincare Ingredient Checker: Look Up Ingredient Information
Sources and further reading
Frequently asked questions
What percentage of vitamin C serum should I use?
For L-ascorbic acid, 10% to 20% is the range with the most evidence. Start lower if your skin is sensitive.
Why has my vitamin C serum turned orange?
It has oxidized through contact with air, light or heat. It is less effective and may irritate, so replace it.
Should I use vitamin C in the morning or at night?
Morning is most common, under sunscreen, because it helps to defend against daytime damage. It can be used at night if you prefer.