Bathroom mold, explained
When Bathroom Mold Is More Than a Cleaning Problem
Bathroom calls split into two groups. Some of it is surface growth on grout lines and caulk, feeding on body oils and soap scum, and a good cleaning handles it. The other kind grows behind the tile, inside the wall cavity or under the floor, where a failed shower pan, a leaking valve or a bad wax ring keeps the framing wet for months.
Silicone caulk is a common trap. When the growth is inside the bead, no spray will reach it; the old silicone gets sliced out with a razor, the gap is dried and treated, and new caulk goes in. Ceilings are the other hot spot: steam from long showers condenses on cold drywall above the tub when the exhaust fan is undersized, isn't run long enough, or vents into the attic instead of outdoors.
In a lot of older baths, the tile was set over standard paper-faced drywall instead of cement board, and that facing feeds mold as soon as moisture reaches it. That's why Bathroom Mold Removal in Stilwell so often involves a plumber and a remediator working the same job.