No.5 Vitamin Concentrated Serum
Reviewed by SerumTruth Editorial · Updated July 2026
A straightforward two-active brightening serum that actually discloses its numbers. 5% niacinamide and 4% tranexamic acid both sit in the studied range and do the bulk of the appearance-of-tone work. Glutathione gets the marketing spotlight, but with no disclosed level it reads as a halo ingredient rather than the reason this works. A solid, fairly priced pick for the niacinamide-tranexamic acid combination.
- Evidence21 / 30
Strength of the research behind the key actives
- Niacinamide: moderate evidence
- Tranexamic Acid: moderate evidence
- Ethyl Ascorbic Acid: moderate evidence
The average of the key actives’ evidence grades.
- Potency20 / 25
Dosed at studied levels, not fairy-dusted
- Niacinamide (5%): dosed at a studied level
- Tranexamic Acid (4%): dosed at a studied level
- Ethyl Ascorbic Acid: present, but below a studied dose
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
- No fragile actives here, so packaging barely moves the score.
Delivery tech plus packaging, and packaging only counts when actives are fragile.
- Formulation7 / 10
Disclosure, active breadth, and ingredient generation
- 2 of 3 actives disclose a concentration
- 3 key actives (breadth credit caps at 3)
- Current-generation or synergistic: Tranexamic Acid, Ethyl Ascorbic Acid
Disclosure, active breadth, and current-generation or synergistic actives.
- Value13 / 15
What a month of use costs vs. the category
- About $16 per month to use
- $26 for 30 ml, used about twice a day (about 0.3 ml each time), so a bottle lasts about 1.7 months
What a month of use costs: full marks at $6 a month or less, the floor at $60 a month or more.
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What’s inside
| Active | Disclosed | Dose |
|---|---|---|
| Niacinamide | 5% | Studied |
| Tranexamic Acid | 4% | Studied |
| Ethyl Ascorbic Acid | n/a | Light |
A brightening serum built on a disclosed 5% niacinamide and 4% tranexamic acid, the two actives doing the real pigment-appearance work, with glutathione, alpha-arbutin, 3-O-ethyl ascorbic acid, adenosine and ceramide NP rounding out the formula at undisclosed levels, in an opaque bottle with a glass dropper insert. The two headline actives sit at sensible, well-studied doses. The glutathione and vitamin C derivative are the marketing hook but read as supporting additions rather than dosed actives. Niacinamide and tranexamic acid are both stable, so the packaging is a minor concern here.
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.