If you're in a modern building with an HVAC system, you probably think of it as a controlled environment: air, relatively clean, either warm or cold depending on the setting, is pumped in for your respiratory benefit. Yet hospitals and schools are some of the worst places to go if you don't want to get sick, even if you never touch a single surface. That's because the air is full of trillions of microbes, and buildings (any buildings) host their own complex ecosystems which we're just now starting to study. Researchers in this relatively new field include biologists as well as architects who are working together to understand the "built environment microbiome." The University of Oregon's BIOBE Center (Biology and the Built Environment) is a hub for this research into what makes a building good for human health, or not.