Also known as: L-ascorbic acid, ascorbyl glucoside, ethyl ascorbic acid
What Is Vitamin C?
Vitamin C is an antioxidant that skin uses to neutralize free radicals from UV exposure and pollution. It is also involved in collagen production, which is why it is often linked with firmer looking skin. The most researched form is L-ascorbic acid, which is effective but unstable. It oxidizes when exposed to air, light and heat, and needs a low pH in the formula to work well.
To address that instability, many products use vitamin C derivatives such as sodium ascorbyl phosphate, ascorbyl glucoside, ethyl ascorbic acid or tetrahexyldecyl ascorbate. These are generally gentler and more stable, though they may act more slowly. Vitamin C is also often combined with vitamin E and ferulic acid, which help stabilize it and support its antioxidant effect.
Vitamin C is a cornerstone for dull skin and hyperpigmentation, and it is one of the best-known partners for daily sun protection.
Vitamin C Benefits for Skin
- Provides antioxidant defense against UV and pollution stress.
- Brightens a dull, tired-looking complexion.
- Helps fade the look of dark spots and uneven tone over time.
- Supports the skin's natural collagen for a firmer look.
- Boosts the protective effect of daily sunscreen.
How to Use Vitamin C
Apply vitamin C in the morning after cleansing and toning, then follow with moisturizer and sunscreen. Start with a lower concentration or a derivative if your skin is sensitive. Our morning routine shows where it fits.
Store it in a cool, dark place and keep the cap closed. If the serum turns dark orange or brown, it has oxidized and is less effective. Wondering about evening actives? See can you use retinol and vitamin C.
Side Effects & Precautions
L-ascorbic acid at higher strengths can sting, tingle or cause redness, especially on dry or sensitive skin. Derivatives are usually better tolerated. Avoid layering it in the same step as strong exfoliating acids if your skin reacts.
Pure vitamin C serums can leave a temporary yellowish tint on skin or fabric as they oxidize, which washes off. Some people also notice small bumps when starting a rich vitamin C oil or cream, usually from the base rather than the vitamin itself. Begin every other day, increase as tolerated, and stop if irritation keeps building.
Use caution when combining
- Strong AHAs or BHAs in the same step
- Very sensitive or compromised skin at high strengths
Frequently Asked Questions
Should I use vitamin C in the morning or at night?
Morning is most common, since its antioxidant benefits support sunscreen during the day. It can also be used at night if that suits your routine better.
Why did my vitamin C serum turn brown?
Browning means the vitamin C has oxidized after exposure to air, light or heat. It is less effective at that point, so it is best to replace it.
Which form of vitamin C is best for sensitive skin?
Derivatives such as ascorbyl glucoside or sodium ascorbyl phosphate are usually gentler than pure L-ascorbic acid. They may work more slowly, but they are easier to use consistently.