In the Western world, humans spend 90% of their time indoors, more since the impact of COVID-19 — but disconnecting ourselves from the outside into sanitized boxes is not as safe as we may think. Caroline Winter explains in Bloomberg Businessweek that while light and air pollution are obvious issues, so is the microbiome of the built environment. The buildings we inhabit are full of microbes; inhale deeply and, “With each breath you bring oxygen deep into the alveoli of your lungs, along with hundreds or thousands of species.” Indoor microbe populations tend to be less healthy for us than those that exist outdoors — and, if you live in a green area, simply opening a window can promote a healthier environment. It may also help to be just a little less clean — ease up on the bleach and we won’t wipe out all the good bacteria with the bad. So don’t be afraid to breathe in a bit of the outside world, or get some mud on you: The microbes from species found on plants and leaves may actually be good for us.

Of course, the most urgent microbe-related question is where to find SARS-CoV-2 and how to kill it. Beyond that, there are also long-term questions. How can we promote indoor microbe populations that don’t make us chronically ill or harbor deadly pathogens? Can we actually cultivate beneficial microbes in our buildings the way a farmer cultivates a field? Experts including Van den Wymelenberg are confident all this is possible. “I really believe our building operators of the future and our designers will be thinking about how to shape the microbiome,” he says.

The term “microbiome” is most often used to refer to the population of microbes that inhabit our body, many of which help produce vitamins, hormones, and other chemicals vital to our immune system, metabolism, mood, and much more. In the typical person, microbial cells are as numerous as those containing human DNA and cumulatively weigh about 2 pounds. In recent decades our personal microbiomes have been altered by factors such as poor dietary habits, a rise in cesarean-section births, overprescription of antibiotics, overuse of disinfectants and other germ fighters, and dwindling contact with beneficial microbes on animals and in nature. According a 2015 study, Americans’ microbiomes are about half as diverse as those of the Yanomami, a remote Amazonian tribe.