Active Ingredients Glossary · V
INCI: Ascorbic Acid / Sodium Ascorbyl Phosphate
Vitamin C is the best-known antioxidant ingredient in skincare: It brightens a dull complexion, reduces dark spots, and protects the skin from free radicals. It's no miracle cure—but it is one of the few ingredients that promote a healthy glow with well-documented efficacy.
What is vitamin C?
Vitamin C (ascorbic acid) is a water-soluble antioxidant that the skin cannot produce on its own. In skincare, it comes in two basic forms: as pure ascorbic acid—the most well-studied, but unstable and slightly irritating at high doses—and as stable derivatives. Sodium ascorbyl phosphate is the most common derivative: gentler, more stable, and converted into active vitamin C only once it reaches the skin. Ascorbyl glucoside and magnesium ascorbyl phosphate also work on this principle.
Rule of thumb: Pure ascorbic acid acts more directly, while derivatives are milder—they're usually the better choice for sensitive skin.
Effects: What's Proven
The antioxidant protective effects, as well as the lightening of dark spots and a dull complexion, are well documented at concentrations of about 10% or higher. Studies also show that vitamin C can support the skin's own collagen production—the effect on fine lines is real but moderate and takes weeks to months to become apparent. Therefore, four out of five bars: solid evidence, although the results depend heavily on formulation, stability, and concentration.
Application & Combination
Traditionally applied in the morning after cleansing and before moisturizer—this is how the antioxidant complements your sunscreen. Store pure ascorbic acid in a cool, dark place: If the serum turns a deep brown color, it has oxidized and should be replaced.
Pairs well with
✓ Niacinamide — soothes and enhances the brightening effect
✓ Hyaluronic acid — provides hydration without any interactions
✓ Sunscreen — the logical addition to your morning routine
Note
! Do not use in the same step as high-dose AHA/BHA peels
! Pure vitamin C oxidizes: store in a dark bottle in a cool place
Vitamin C in the BONSANA lineup
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Vitamin C for Your Glow
Serums, masks, and creams with vitamin C—trusted brands, ready to ship from our Swiss warehouse.
Discover facial serums →Frequently Asked Questions About Vitamin C
When should I apply vitamin C—in the morning or at night?
Morning is the standard: As an antioxidant, vitamin C complements your daily sunscreen. It works just as well in the evening—for example, as a night cream like the Triple C Night Cream.
Is Vitamin C compatible with niacinamide?
Yes. The supposed conflict is a myth stemming from old lab studies. Modern formulations actually combine both active ingredients intentionally—you can apply them one after the other without any concerns.
My serum has discolored—can I still use it?
A slight yellowish tint is normal for pure ascorbic acid. A deep orange-brown color means it has oxidized. In that case, the serum is no longer effective and should be replaced.
What concentration is best for beginners?
5–10% or a gentle derivative like sodium ascorbyl phosphate. 20% is effective but may cause a tingling sensation at first—increase the concentration gradually and monitor your skin's reaction.
