Vitamin C (LAA)

• Measured on: investigator-graded photodamage on the treated half-face (fine wrinkling, roughness, tone).
• Two small randomised double-blind vehicle-controlled half-face trials carry this ingredient, and both report at 12 weeks.
• In the first, Cellex-C High-Potency Serum — ascorbic acid with acetyl tyrosine, zinc sulfate, sodium hyaluronate and green tea extract — ran against its own vehicle serum on opposite halves of 19 evaluable faces for three months, with optical profilometry of surface topography alongside clinical, photographic and patient grading; the contrast there is a multi-active serum against vehicle, not ascorbic acid isolated.
• In the second, 10% ascorbic acid plus 7% tetrahexyldecyl ascorbate in an anhydrous polysilicone gel ran against the same gel base in 10 patients, with clinical evaluation at weeks 4, 8 and 12; interim visits therefore existed, but separation was reported only at the endpoint (cheeks P=0.006, perioral P=0.01, overall P=0.01), so 12 weeks is a ceiling and true onset may be earlier.
• Both trials are very small.
• For pigment the picture is weaker rather than faster: 5% ascorbic acid against 4% hydroquinone in melasma over 16 weeks improved subjective scores but was clearly inferior to hydroquinone.
• Formulation matters more than duration here, since an oxidised or high-pH serum delivers nothing at any timepoint.

PMID:10522500 (Traikovich, Arch Otolaryngol Head Neck Surg 1999; Cellex-C High-Potency Serum vs its vehicle, half-face, 19 evaluable patients, 3 months, optical profilometry plus clinical and photographic grading). PMID:11896774 (Fitzpatrick & Rostan, Dermatol Surg 2002; 10% ascorbic acid + 7% tetrahexyldecyl ascorbate in anhydrous polysilicone gel vs the gel base, half-face, 10 patients, evaluated at weeks 4, 8 and 12, significant at week 12). The 16-week 5% ascorbic acid versus 4% hydroquinone melasma comparison is described without a PMID, which I could not verify.