Melasma is acquired, chronic and relapsing. It sits on the cheeks, forehead, upper lip and jaw; it is far more common in women; and it is more common and more stubborn in darker skin types. Ultraviolet light, visible light, hormones and a vascular component all contribute.
It is not a stain on the surface, and it does not behave like one. That single sentence explains most treatment failures.
How the review was built
A PubMed search to October 2018, restricted to randomised and controlled clinical trials in English, plus the Cochrane database. Two hundred and twelve citations, of which 113 studies met inclusion criteria — 6,897 participants in total. Treatments were grouped into topical agents, chemical peels, laser and light devices, and oral agents.
Note the cut-off date. This is the best map of the evidence up to 2018, not a snapshot of 2026. Later work has mostly refined two things — tranexamic acid and device safety in darker skin — rather than overturned the ranking.