For treatment, first identify the moisture source. Wipe a small area with a paper towel; if it smears, it’s likely soot or dirt. If it’s granular and doesn’t wipe away easily, it’s mold. For a small patch (under one square meter), you can clean it yourself with a diluted detergent solution or a vinegar-water mix. Always wear an N95 mask and gloves. Merely painting over it will not work—the mold will bleed through.

The critical step is fixing the humidity to prevent recurrence. Your AC may be set too cold, causing extreme temperature differences that promote condensation. Ensure it’s set to 23-24°C. Check that the AC unit is properly sized for the room and that its drain line is not clogged, as a blockage can cause excess humidity. Improving air circulation in the room with a fan can also help prevent stagnant, moist air from settling on cold surfaces.

For a recurring or large-scale problem, the underlying cause could be more complex, such as a minor plumbing leak inside the wall or insufficient insulation around AC ducting. In these cases, a professional inspection is warranted to identify the exact condensation point and recommend a targeted solution, which is the only way to achieve a permanent fix.