Is your house making you sick?

Researcher Jean F. Ruiz-Calderon, collecting environmental data. (credit: Humberto Cavallin)

If you live in a city, each room of your house has its own distinct broth of microbes splattered all over its walls--most of it from your skin, mouth, and gut. But if you live in a rural area, this broth contains a lot more microbes from the environment outside. Now, scientists in the burgeoning field of "microbial biogeography" say this could help us understand why people in cities tend to develop diseases that are very different from people in the country.

Your body is full of microbes--indeed, a recent estimate suggests there are more single-celled aliens in your body than there are human cells. The average human male has about 30 trillion cells, and 40 trillion microbes living inside him. But these little invaders don't stop at the envelope of your flesh. They're constantly being sloughed off with your skin, dribbling out of your mouth, and getting pooped out of your colon. Which is where microbial biogeography comes in. It's the study of all the microbes that live in our environments, whether they come from us, other animals, or elsewhere in the natural world. Taken together, the microbes in an environment--whether it's your gut or the forest floor--are called a microbiome.

There have already been efforts to sequence microbiomes in people's homes, in the soils and waters of many different environments, and (memorably) on the New York City subway. From these experiments, we've learned that our environments are crawling with different kinds of microbes, many of which co-evolved with us and contribute to our good health. Now a new study conducted in and around Brazil reveals that the microbiomes in our homes change dramatically from country to city, and even from room to room in urban homes.

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