Hey Niksik - have you tried opening the windows? I know that sounds a bit weird, but fresh air going through the house is actually a big help. It brings in new, clean air (depending on where you live though) and gets rid of the stale stuff. People who shut up their doors and windows, breathe the same air day after day...not healthy. I read this article in a health magazine a few years back about the "sick building syndrome" which described how people who live and work in poorly ventilated buildings get sick more often than those who get fresh air. The theory was that if you breathe the same air day in and day out, that air will inevitably get full of germs and bugs that people bring in and if there's no ventilation, all that bad stuff stays there and keeps making people sick.
Hope that helps.