New research suggests that one of the leading sources of air pollution in your home is probably …you. In fact, your presence in a room can add millions of bacteria to the air every hour, according to a new study conducted by Yale University and the University of California, Berkeley. The research was conducted in a classroom setting while the room was both occupied and unoccupied. The researchers concluded that most, but not all, of the bacteria and other contaminants in the air were already in the room and were stirred up when humans entered the environment. “Mostly people are re-suspending what’s been deposited before,” one of the team told Yale News. Most of the stirred-up airborne microbial stewcame from the floor, he said.

That conclusion suggests that your indoor carpet actually functions as an air purifier, at least so long as nobody in the room stirs thing up (by, say, walking or moving). As ineffective as that might seem, it’s similar to how ionizing air purifiers actually work by charging particles that then stick to surfaces in your home. Sooner of later those particles (which your ionizer caused to cling to the wall or carpet) relaunch into the air. Then, they wind up sticking to your lungs.

In the Yale study, the principal investigator noted that carpeted rooms in particular retain high levels of microorganisms from the air. If you suffer from asthma, you may already know this. Carpeting can be a haven for pet dander, pollen and other allergens. A high-quality HEPA vacuum can help, as can frequent steam cleaning of carpets. But vacuuming carpets, even with a HEPA vacuum cleaner, can also disturb particles and cause them to become airborne, the American Lung Association points out. So do you have to get rid of the carpets in your home? “Replacing carpet with hard flooring may be a good idea,” concludes Mayo clinic asthma and allergy expert Dr. James Li (http://www.mayoclinic.com/health/asthma-triggers/AN01948), Of course, as Li and others note, the hard flooring you install may itself be a source of another indoor air quality hazard: volatile organic compounds (VOCs).

The researchers in the Yale/UC Berkeley study also found that about 20 percent of all of the bacteria and fungi launched into air by humans is of human origin, as opposed to coming from plants or other sources. The average human emission: about 37 million bacteria per hour.