Plenty of daylight makes it harder for bacteria to survive?

Even before Florence Nightingale advised that hospitals be designed to let daylight in, people observed that sunshine helps keep you healthy. But there was not much research to explain why that's the case, especially inside buildings.

Researchers at the University of Oregon set up a study of dusty, dollhouse-size rooms to compare what happens in rooms exposed to daylight through regular glass, rooms exposed to only ultraviolet light and those kept dark, National Public Radio reports.

They used a mix of dust collected from actual homes in the Portland area and let the miniature rooms sit outdoors while keeping the insides at a normal room temperature.

After 90 days (because that's how long dust can hang around, even if you vacuumed), they sampled the dust and analyzed the types of bacteria present. What they found surprised them and confirmed that rooms exposed to daylight have fewer germs.

In fact, the study showed that the lit rooms had about half the viable bacteria (those that are able to grow), compared with dark rooms. Rooms that were exposed only to UV light had just slightly less viable bacteria than ones exposed to daylight.

One surprising thing was the amount of microbes that were viable in dust, as indoor dust is like a desert — it's too dry for most bacteria or other things to grow.

This study found 12% of bacteria in dark rooms were viable compared to 6.8% in rooms with daylight and 6.1% in rooms exposed to UV light only.

The daylit rooms in the study also had less of the types of bacteria associated with human skin, which people shed as they move around indoors, and more closely resembled outdoor bacterial communities. Some of the human-associated bacteria species that didn't survive in the lighted rooms are from a family of bacteria known to cause respiratory disease.

In their future work, the researchers said they'd like to design studies to determine how much light is necessary to kill microbes so architects can begin to design buildings with that in mind.

Also, researchers have learned from trying to eradicate all germs in hospital and laboratory clean rooms that it's really hard to get rid of microbes wholesale. They believe that sanitizing isn't the best approach, as some microbes are actually good for us, like the ones in yogurt, for example.

They even suggest that it may be better to enrich an indoor setting with microbes that are not harmful or even with those that are beneficial.

University of Oregon

daylight in rooms

influence of daylight in rooms

UV light

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