I was told that you should have your carpets cleaned with some sort of steam cleaner (professional, store borrowed or bought) every 3 months in order to remove all the germs and traffic marks. We bought a pretty nice one for under $300. I know that's not on most people's lists to buy or in the budget but it's certainly paid for itself over the past few years. We just cleaned ours a few weeks ago and it almost wants to make you puke after seeing what comes out of your carpets.