Adding 20% Vitamin C to Yellow Light Therapy Cut Melasma Scores Further in a 12-Week Placebo Trial

Melasma is one of the hardest pigmentation problems to shift, and a trial published on 23 August 2026 in the Journal of Cosmetic Dermatology tested whether vitamin C adds anything to a light-based treatment that dermatology clinics already use.

Researchers at West China Hospital, Sichuan University, randomly assigned 71 adults with melasma to two groups. Both received yellow LED light at 590 nanometres twice a week for twelve weeks. One group then applied a 20 percent L-ascorbic acid essence after each session; the other applied an identical-looking vehicle with no vitamin C. Neither patients nor assessors knew who had which. The vitamin C was not started at full strength: it was stepped up through 2.5, 5 and 10 percent over the first three weeks, and the powder and liquid were mixed fresh before each use. Sixty-one people completed the study.

On the main measure, the modified MASI severity score, the vitamin C group fell by an average of 1.95 points against 0.69 in the light-only group, a difference the authors report as statistically significant. Instrument readings pointed the same way: the melanin index dropped by about 13 units with vitamin C and about 3 without. Physician grading and patient satisfaction also favoured the combination, while barrier measures such as water loss did not differ between groups.

The cost was some irritation. Six of the 35 people in the vitamin C group reported redness and stinging; five cases cleared within a day, and one moderate case took a week and was treated with an oral antihistamine. Nobody in the placebo group reported a reaction.

Three limits matter. Follow-up stopped at twelve weeks, so there is no information on relapse, which is the central problem with melasma. Sun-protection habits were not monitored. And the trial was part-funded by Galenic, the French laboratory that supplied the serum, although the paper states the sponsor had no role in design, analysis or publication.

The study tests an in-clinic protocol, not a shop-bought serum used at home, and anyone with melasma should take its findings to a dermatologist rather than try to recreate it.