Stay out from under a sagging or bulging ceiling. Water near lights, fans or other electrical fixtures adds another hazard. Do not puncture the ceiling to release water or climb up to investigate.
Keep the area clear
Move people and pets away without walking beneath damaged material. Do not operate a wet light or ceiling fan. Active danger, falling material or an electrical emergency calls for emergency services or the relevant qualified professional, not an online request form.
Describe what changed
From a safe place, note whether the mark is new, spreading or associated with rain, plumbing use or an upstairs appliance. Water can travel along building elements before appearing. A stain under a bathroom is a clue, not proof of the source.
Coordinate source repair and moisture assessment
A plumber, roofer or other trade may be needed for the source. Interior assessment considers the ceiling, wall edges, insulation and adjacent spaces where accessible. Ask what remains inaccessible and what must be checked before patching or repainting. A dry-looking surface does not establish that concealed layers are dry.