What the topical studies tested

Tranexamic acid has been studied as a topical intervention for melasma, a defined pigmentation disorder. That research should not be converted into a promise that any over-the-counter tone serum will fade every type of mark. In a double-blind split-face trial, Thai women with bilateral epidermal or mixed melasma applied a 5% tranexamic-acid liposomal gel to one side and its vehicle to the other, twice daily for 12 weeks; sunscreen was used across the face. Twenty-five were enrolled and 21 completed the trial. Both sides improved relative to their own baselines, but the investigators found no statistically significant difference in pigmentation outcomes between the tranexamic-acid and vehicle sides at 12 weeks. The treated side had a higher measured erythema index than the vehicle side at study end. Improvement from baseline alone would therefore be a misleading way to present this trial as proof of an ingredient-specific effect.

What the active-comparator study adds

A separate randomized, single-blind trial assigned participants with melasma to topical 5% tranexamic-acid solution or 3% hydroquinone cream once daily, alongside SPF 30 sunscreen, for 12 weeks. Of 120 included, 100 were analyzed, 50 per group. The measured reduction was 27% in the Melasma Area and Severity Index (MASI) in the tranexamic-acid group and 26.7% in the hydroquinone group; the between-group difference was not statistically significant. This is not an equivalence or non-inferiority trial, so that result does not establish that the treatments perform identically. Nor can the comparison isolate the effect against no active ingredient: both groups used sunscreen, there was no vehicle-only arm, and the solution and cream were different types of preparation. Short duration and differences between preparations limit the comparison.

Applying the evidence carefully

The two trials test particular 5% topical preparations, schedules, groups of patients and clinical outcomes; they do not test lower-strength retail mixtures, long-term recurrence, or all causes of uneven tone. The split-face comparison and active-comparator comparison answer different questions, and their results should be reported side by side rather than averaged into a universal claim. Melasma studies are not trials of lactic acid; tranexamic acid is not an AHA exfoliant. A proposed biological mechanism for the split-face gel does not overturn its negative vehicle-controlled result.

Claims and routes

Appearance-focused cosmetic language is not a clinical treatment claim for diagnosed melasma. In the US, a product’s intended use, including disease-treatment claims, determines whether drug rules apply. Oral, injected and topical administration must not be treated as interchangeable: these trials concern topical application and cannot establish safety or efficacy for taking the substance by mouth. Both studies incorporated sunscreen, so sun protection was part of the tested context, not a dispensable footnote. For what UV labels actually signify, see broad-spectrum sunscreen. Neither trial validates any specific commercial serum or an untested combination of ingredients.