Autumn does not invent mold. It simply clears away every obstacle standing in its path, and it does so outdoors long before anything shows up on your walls.
That is the framing offered by Michael Rubino, a mold and air quality expert and the founder of HomeCleanse, in advice published by Tom’s Guide on September 12, 2026. The season’s first problem, he says, is the yard. “As leaves fall and vegetation dies back, that material collects on the ground and begins to decompose,” Rubino explains, and fungi are the organisms doing the decomposing. Wind and ordinary yard work lift the resulting spores into the air, after which the trip indoors is short: “Once airborne, they can enter the home whenever doors or windows are opened or be tracked inside on shoes, clothing or pets.”
Three more seasonal factors stack on top of that. Hurricane season and heavy rain bring the kind of water damage that mold feeds on. Gutters packed with debris stop draining and let moisture pool against the structure. And as the weather cools, houses get sealed up, ventilation drops, and whatever came inside stays inside. Rubino’s rule is blunt: “Wherever there’s prolonged moisture, there’s an opportunity for mold.”
The number that matters is relative humidity. Rubino recommends holding indoor humidity between 35 and 50 percent, and warns that mold can grow at a relative humidity level of 60 percent. That makes a hygrometer the cheapest diagnostic tool in the house, because you cannot manage a figure you are not measuring. If the reading runs high, a dehumidifier is the fix; Tom’s Guide names the Midea Cube 20 Pint as its budget pick for small spaces.
The most useful trick in the whole piece costs nothing. Lift the lid off your toilet tank and look at the underside. That surface sees almost no air transfer, so if mold is growing there, it points to high levels of spores circulating elsewhere in the home. Think of it as a canary rather than a cleaning chore.
From there, Rubino points to the places mold actually hides:
- Under sinks and around plumbing supply lines
- Behind major appliances such as refrigerators, dishwashers and washing machines
- Behind furniture pushed against exterior walls
- Inside dark cabinets and closets
- Around chimneys, fireplaces, skylights and recessed lighting
- Inside attics, basements and crawlspaces
- Garages and storage zones
- Windowsills, window frames and door frames
- Mattresses, upholstered furniture and carpet padding
- HVAC systems, specifically drip pans, coils and vents
- Bathroom exhaust fan housing
None of this is about sterilising your house. Spores are always present, and the goal is to deny them the one variable you can actually control. As Rubino puts it, “Focus on reducing unnecessary accumulation indoors, and importantly, control moisture, so those spores don’t have the conditions they need to begin growing.” Clear the gutters, dry the wet spots, watch the hygrometer, and check the tank lid.
