Melasma questions tend to arrive together: why it appears, how it looks, and what can be done about it. Each gets a short answer here.
What sets melasma off
The AAD names sunlight, taking birth control pills, and even stress as triggers for melasma. Sun is the trigger that shows up in the treatment advice too, which is covered below.
How the patches look
According to UCLA Health, the patches appear as flat or slightly raised areas of varying shades of brown.
Sun protection in a melasma plan
The AAD lists sun protection as part of a treatment plan. Its reason is that sunlight causes the skin to make more pigment, which can darken existing melasma and cause new patches.
For a plain description of the condition, read the MedlinePlus melasma encyclopedia entry and the AAD melasma overview.
When your sun exposure changes
The sun point matters most when your exposure changes. A patch that darkens or spreads is worth showing to a dermatologist, who can decide what comes next.