C-Firma Fresh Day Serum
Reviewed by SerumTruth Editorial · Updated July 2026
The mix-it-yourself format is a real answer to the oxidation problem that dogs L-ascorbic acid, and the antioxidant trio has strong evidence behind it. You pay a prestige price and you have to use it within a few months of mixing. For a fresh, well-packaged 15% vitamin C, it delivers.
- Evidence24 / 30
Strength of the research behind the key actives
- Vitamin C (L-Ascorbic Acid): strong evidence
- Vitamin E (Tocopherol): moderate evidence
- Ferulic Acid: moderate evidence
- Score is the average of the key actives’ evidence grades.
- Potency21 / 25
Dosed at studied levels, not fairy-dusted
- Vitamin C (L-Ascorbic Acid) (15%): dosed at a studied level
- Vitamin E (Tocopherol): dosed at a studied level
- Ferulic Acid: dosed at a studied level
- Potency tracks how strongly the actives are dosed, led by the strongest, not how many there are.
- Delivery & stability16 / 20
Delivery tech + packaging that protects fragile actives
- Delivery: standard
- Packaging: airless, opaque
- Air- or light-sensitive actives (Vitamin C (L-Ascorbic Acid), Vitamin E (Tocopherol), Ferulic Acid), so packaging is scored.
- Formulation7 / 10
Disclosure, active breadth, and ingredient generation
- 1 of 3 actives disclose a concentration
- 3 key actives (breadth credit caps at 3)
- Current-generation or synergistic: Vitamin C (L-Ascorbic Acid), Vitamin E (Tocopherol), Ferulic Acid
- Value5 / 15
What a month of use costs vs. the category
- About $50 per month to use
- $78 for 28 ml, used about twice a day (about 0.3 ml each time), so a bottle lasts about 1.6 months
- Band: $6/month or less earns full marks, $60/month or more hits the floor.
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What’s inside
| Active | Disclosed | Dose |
|---|---|---|
| Vitamin C (L-Ascorbic Acid) | 15% | Studied |
| Vitamin E (Tocopherol) | n/a | Studied |
| Ferulic Acid | n/a | Studied |
A two-part fresh-mix system: you pour the liquid base into a vial of 15% L-ascorbic acid powder and shake before first use, so the vitamin C is not sitting pre-dissolved and oxidising on the shelf. Vitamin E and ferulic acid round out the antioxidant side, and the mixed serum lives in an opaque pump. Once activated it is meant to be used within about six months.
How it’s delivered
Air- and light-sensitive actives (vitamin C, copper peptides) lose potency fast in the wrong packaging, so delivery and the bottle are scored, not just what’s on the label.
The actives, explained
Cosmetic information for general education, not medical advice. The SerumProof score reflects our reading of publicly available research and formulation disclosures. See how scoring works.