There is some additional risk with modern homes being much better sealed than old homes which always had some air moving through it. If you don't have a proper

There is some additional risk with modern homes being much better sealed than old homes which always had some air moving through it. If you don't have a proper HVAC system and use like electric heaters instead of forced air, humidity levels can build up and slowly absorb into materials if you don't have enough airflow, and you likely won't notice, unless maybe the dew point gets high enough that all of a sudden every surface in your house is damp. It is less of a concern in places without high humidity but some swampy areas can be 90% humidity for weeks or months at a time and then all of a sudden you got mold behind your walls because some idiot decided to seal up every seam with plastic or glue or whatever other impermeable material. Part of this is a misunderstanding of building techniques that block airflow, ive seen numerous houses with all the roof vents plugged up to "save heat", walls with plastic sheeting on the inside wall creating air/moisture traps, or people replacing air-permeable house wrap with solid sheet plastic, foam and glue on every board and seam with a sealed up and moist crawl space underneath, ect. It is fairly easy to get mold in a humid place with a sealed home and no forced air, and nearly impossible to kill it all without tearing out all the drywall in the house. If everything was done right, shouldn't be a problem, but people are far more likely to pay for size and speed over quality materials or careful quality labor.