A sun spot sits in one place and can be removed. Melasma is an ongoing process — pigment-producing cells that are overactive and easily provoked, driven by a combination of sun, heat, hormones and genetics.
That is why a treatment that works beautifully on a lentigo can disappoint on melasma, and why melasma comes back.
It is also why heat matters. Lasers deliver heat, and heat is one of the things that provokes melasma. That tension sits underneath everything below.
Studies of 1927 nm lasers — the wavelength Moxi uses — show a real short-term effect and a much less certain long-term one.
Short term, it works. One study of 100 patients reported a large drop in melasma severity scores after two sessions. A smaller retrospective series found significant improvement at one week, one month and two months.
Longer term, the evidence splits. That same small series — eleven patients — found the improvement no longer significant at three months. But a randomised split-face trial in 46 people still found benefit at three months. By six months in that trial, severity scores were still improved from baseline while the objective melanin measurement on the laser-only side was not.
Worth knowing about that trial: it compared laser plus tranexamic acid against laser alone. "The laser-only side" means the side that did not also get the drug.
The published study of Moxi specifically was not a melasma study — it looked at pigment generally in 27 people, and even there the result had regressed toward baseline at three months.
No published relapse rate for this treatment exists. If a clinic gives you a specific percentage, ask where it comes from.
This is the part that deserves weight.
In a retrospective study of 856 non-ablative fractional laser treatments, melasma worsened in about 0.9% of cases and darkening afterwards occurred in about 1.1%. Worth noting what that study actually was: mostly 1550 nm rather than Moxi's wavelength, in Fitzpatrick III–IV skin. No equivalent figure exists for Moxi.
Those are small numbers, but melasma is a condition where a bad outcome is stubborn and visible, and where the person seeking treatment is often already frustrated by it.
A network meta-analysis of melasma treatments ranked non-ablative fractional lasers and picosecond lasers below:
A separate meta-analysis went further and found neither non-ablative fractional nor picosecond lasers produced a significant reduction in melasma severity.
That does not make laser useless. It means it is not where a sensible plan starts.
Melasma responds best to a layered approach, and the parts of it that are least glamorous are the ones that carry the most weight.
If you have been offered a laser as an opening move for melasma, that is worth a second conversation.
If you get cold sores, tell your provider. Laser treatment can reactivate the virus, and antiviral medication started in advance is the standard precaution.