It pretty much implies leaky windows, otherwise the house would become a vacuum and everyone in it would suffocate.
Toxic fumes from paint and cleaning products, etc are a similar issue- they just get circulated forever.
The "right" solution would be to mandate fresh air ventilation be incorporated into home HVAC systems like they do in commercial designs. So, you turn on an exhaust fan, you draw in fresh outside air through the HVAC system that conditions it before dumping it into the house, etc. Nobody wants to do this because it's sounds like you're wasting energy, but it's just one of those things you need to do to prevent a sick home.
