Grandma was right: Sunshine helps kill germs inside

Scientists from the University of Oregon used real dust from Portland homes to test the effects of sunlight, UV light and darkness on the bacteria found in the dust.

Dave G Kelly / Getty Images


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Dave G Kelly / Getty Images

Scientists from the University of Oregon used real dust from Portland homes to test the effects of sunlight, UV light and darkness on the bacteria found in the dust.

Dave G Kelly / Getty Images

Even before Florence Nightingale advised that hospitals be designed to let in daylight, people would observe that the sun helps keep healthy. But there was not much research to explain why this is the case, especially within the buildings.

Researchers at the University of Oregon set up a study on the doll's dusty halls to compare what happens in rooms exposed to daylight through normal glass, rooms exposed to ultraviolet light only, and those held at the time. darkness. They used a mix of dust collected from real houses in the Portland area and let the miniature rooms sit open while keeping the interior at a normal room temperature.

After 90 days (because it is the duration of the dust, even if you have vacuumed), they sampled the dust and analyzed the types of bacteria present, sampled the powder and analyzed the types of bacteria present.

What they found surprised them and confirmed what your grandmother already knew: the rooms exposed to the light of day have fewer germs. In fact, the study showed that the illuminated rooms had about half the vital bacteria (those that are able to grow), compared to dark rooms. The rooms exposed to UV rays only had slightly less vital bacteria than those exposed to daylight. Their research was published Wednesday in the journal Microbiome.

Since we spend so much time indoors, the new research could give an idea of ​​the relationship between air quality and light. "I think it's a novel study because they looked at the effect of visible light, and they were also looking at real bacterial communities and real household dust," says Linsey Marr, a professor of civil and environmental engineering at Virginia Tech, specializing in indoor air quality and was not involved in this study.

The lead author of the study, Ashkaan Fahimipour, postdoctoral researcher at the University of Oregon & # 39; s Biology and the Built Environment Center, says he is surprised that visible light and UV light have worked similarly for keep the bacteria down.

The researchers examined both types of light because UV is known to be a good disinfectant and is used to clean drinking water. However, the typical window glass filters most of the UV light.

Another surprising thing was the amount of microbes that were vital in the dust. Previous studies did not suggest it would be so much, says co-author Kevin Van Den Wymelenberg, co-director of the Center for Biology and Built Environment at the University of Oregon. This is because the apartment dust is like a desert – it's too dry for most bacteria or other things to grow. This study found that 12 percent of the bacteria in the dark rooms were passable compared to 6.8 percent in rooms with natural light and 6.1 percent in rooms exposed to UV rays alone.

Although it may not seem like much, "6% of millions of cells is still a lot of microbes," says Van Den Wymelenberg. "Until now, daylight [illuminating a building with natural light] it concerned visual comfort or general health. But now we can say that daytime lighting influences the quality of the air ".

The day lit rooms in the study also had fewer types of bacteria associated with human skin, which people lose as they move inside, and look more like open bacterial communities. Some of the species of bacteria associated with humans that do not survive in lighted rooms come from a family of bacteria known to cause respiratory illnesses.

In their future work, the researchers said they would like to design studies to determine how much light is needed to kill the microbes so that architects can start designing buildings with this in mind.

In addition, researchers have learned from trying to eradicate all the germs in the cleanrooms of hospitals and laboratories that it is really difficult to get rid of the wholesale microbes. "Hygienization is not the best approach," says Fahimipour. And some microbes are really good for us, like those in yogurt. One day, he says, "it could be better to enrich an indoor environment with microbes that are not harmful or uniform [with those that are] beneficial. "

Kathleen O & # 39; Neil is a freelance writer who lives in the Washington area, D.C. ,.

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