Think about this for a minute. You are never alone. But not in the government spy-way you might be thinking. No, no, we’re talking about microbes! If you read our post about Microbes and You, then you already know that our bodies contain trillions of microbes. We pick these microbes up from just about everything we touch, but what about the air we breathe? And have you ever considered the amount of microbes that you might brush off back into your surroundings at any given moment?

When You’re in the Room, Microbes Surge

This is a love song waiting to happen. Yea, yea, we know: we’re overly enthusiastic about microbes. But there are more of them then there are of us. We’re outnumbered, so we’re flattering them just in case.

Jordan Peccia, associate professor of environmental engineering at Yale, once said, “We live in this microbial soup, and a big ingredient is our own microorganisms.” Peccia was also the primary investigator, along with other Yale engineers, of a study published online by the journal, Indoor Air, and according to their research, your mere presence in a room can add 37 million bacteria to the air every hour.

Oh, and those bacteria are primarily leftovers from the previous person or stirred up from the floor. (This isn’t quite the love story we were hoping for.)

According to Peccia, “Mostly, people are re-suspending what’s been deposited before. The floor dust turns out to be the major source of the bacteria that we breathe.”

The research team measured and analyzed biological particles in a single, ground-floor university classroom over an 8-day period – 4 days when the room was occasionally occupied, and 4 days when the room was unused. Windows and doors were kept closed at all times, and the HVAC system was operated at normal levels.

Microbe Results

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The researchers found that “human occupancy was associated with substantially increased airborne concentrations” of microbes.

They even sorted the particles by size! Occupancy resulted in especially large spikes of larger-sized fungi and medium-sized bacteria. In this case, size is important because it affects the degree to which the microbes are likely to be filtered from the air or linger and recirculate.

The researchers found that about 18% of all bacterial emissions in the room, including fresh and previously deposited bacteria, came from humans. Other sources could be plants, soil, water, etc.

The group also found that rooms with carpet seem to retain especially high amounts of microorganisms, but they noted that this doesn’t necessarily mean rugs and carpets should be removed. Very few of the microorganisms commonly found indoors (less than 0.1%) are infectious.

Many previous studies have surveyed the variety of germs present in everyday spaces, but this was the first study to quantify how much a single human presence can affect the level of indoor biological aerosols.

So just remember, you are never alone. You’re surrounded by your own microbes and the microbes of others. Whether or not that’s comforting, we’re not entirely sure.

The research paper’s lead author is J. Qian of Yale. Other contributors are D. Hospodsky and N. Yamamoto, both of Yale, and W.W. Nazaroff of the University of California–Berkeley.

The research was supported by the Alfred P. Sloan Foundation.