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 harder cases are growing out of sight, in the wall behind the tub surround or in the subfloor, kept damp by a cracked shower pan liner, a dripping valve body or a toilet seal that's been seeping for a long time.
People fight caulk mold for years without winning. 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 Plymouth so often involves a plumber and a remediator working the same job.