Great News! Pollutants in the air filter through your carpet. The carpet traps them so you don't breath them over and over. But what happens when the trap gets full? Your family starts breathing dust mite debris, pollens, pollutants, fungus, spores, bacteria and a long list of other really gross stuff. Once your carpets natural filtering ability gets full, it is time for a thorough cleaning for your health's sake. Clean every six months and you will breath easier.