09/21/2026
Mold usually needs three things: moisture, a food source, and enough time. The moisture is the part that's most often overlooked.
Common causes include:
Leaking pipes or plumbing — even a slow leak inside a wall can support mold.
Roof or gutter leaks — water can travel surprisingly far from where it enters.
High indoor humidity — especially when humidity stays above about 60%.
Condensation — around windows, cold exterior walls, pipes, or air-conditioning equipment.
Poor bathroom ventilation — showers create a lot of moisture, especially without an exhaust fan.
Basements, crawl spaces, and foundations — groundwater or damp soil can raise indoor moisture.
Flooding or previous water damage — mold can develop if materials weren't dried thoroughly.
Air-conditioning problems — clogged drains, frozen coils, or poorly draining condensate can create persistent moisture.
Wet carpets, drywall, insulation, or furniture — porous materials can retain water long after the surface feels dry.
Poor airflow — stagnant air can allow moisture to accumulate in closets, behind furniture, and against exterior walls.
Improperly vented dryers or exhaust fans — sending moist air into the home rather than outdoors.
