Mold is a kind of fungus. Tiny spores are everywhere — outdoors, indoors, on surfaces, in the air. Most of the time, your body handles them without you noticing.
Mold becomes a concern when moisture lingers indoors and lets a colony grow on building materials. The species, the amount, and your individual sensitivity all matter.
Common indoor sources of moisture
- Plumbing leaks behind walls, under sinks, around toilets
- Roof leaks
- Bathrooms with poor ventilation
- HVAC systems that condense water and don't drain it
- Floods, even ones that "dried out" days later
When to take a closer look
If you notice any of these in your home, hotel room, or rental, it's worth investigating:
- A persistent musty or earthy smell
- Visible discoloration on drywall, ceilings, or grout that wasn't there before
- Symptoms (sinus, sleep, brain fog) that worsen in one specific building and improve when you leave it
- A history of water damage in the building
What this is not
This is general information, not a diagnosis. If you're concerned about a health condition, please talk to a qualified practitioner. If you're concerned about a property, an inspector or testing service can give you data — see the testing services page.
We meet people where they are. Many readers come to us scared and dismissed by other systems. You are not crazy for asking these questions.