A patch of mold bigger than a couple of square feet calls for a professional look, not a scrub brush. But you don't need to see mold for it to be a problem worth addressing. A musty smell that lingers in a bathroom, hall closet, or laundry room usually means something is growing behind the wall or under the floor. If anyone in the house has allergies that flare up at home and clear up elsewhere, a cough that comes and goes, or headaches tied to time spent indoors, it's worth ruling out spores in the air.
Anaheim's older housing stock makes this more common than people expect. West Anaheim and central Anaheim are full of 1950s and 60s single-story homes with crawl spaces below and attics above, both classic places for moisture to sit undetected, and the galvanized plumbing running through many of them is well past its expected lifespan. In Anaheim Hills, where the two-story hillside homes were mostly built between the 1970s and 90s, an upstairs bathroom leak often shows up as a stain on the ceiling below long before anyone finds the source. And in the Colony Historic District, the original wood framing and raised foundations under those Craftsman bungalows create crawl spaces that trap moisture from old, slow leaks nobody's checked in years.