The home is the number 1 killer because of the MOLD and your own breathe being trapped. I also assume these trillions of creatures grow our own germs and allow us to rebreathe back in super germs.
Many houses are water damaged and condemed, only to be sold and redone and the next buyer knows nothing about the house being full of mold under the new paint and carpet.
We have always lived on a hill in the country no matter how many times we moved, I am glad for this! A dry house is a blessed house when it comes to the mold problems.
The whole house ozone machines are suppose to kill the hidden molds.