This is a good article about some of the mistakes people make when trying to have clean air in their home.  Sometimes we use air fresheners to cover bad odors.  This only masks the odor, bacteria, particles in the air, but does nothing to remove them.   Any particles, germs, odors, viruses released inside is about 1,000 times more likely to be breathed in than something released outdoors.

http://www.nytimes.com/2009/05/14/garden/14fix.htm...