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Be Careful How You Clean

A picture of a spitting spider
Matt Bertone

Hosting family and friends for the holidays often means a lot of mopping, sweeping and scrubbing. However, biologist Rob Dunn says people need to use moderation in their cleaning. Pesticides and antimicrobials kill off many beneficial species that live indoors and eliminate competition for resistant species like German cockroaches, bedbugs and MRSA bacteria.

Many products claim to kill 99 percent of bacteria, but Dunn says people should worry about the one percent left behind. The biologist talks to host Frank Stasio about the many organisms that share our homes and how humans are speeding up the evolution of the indoor biome.

Dunn is the author of “Never Home Alone: From Microbes to Millipedes, Camel Crickets, and Honeybees, The Natural History of Where We Live” (Basic Books/2018). He is also a professor in the department of applied ecology at North Carolina State University.


There's a microbe that lives only in hot water heaters and then in places like hot springs in Yellowstone. There's a spider that runs around in your kitchen ... And it spits a ball of venomous silk on fruit flies. It's a whole kind of wilderness [in your home]. - Rob Dunn

Dunn on the importance of microbes to the human body:

Your body really isn't in isolation. Everything that your body is is a connection to the rest of life. And so your gut doesn't work — doesn't digest properly  — unless it has microbes in it. Your skin doesn't really work unless it has a layer of microbes on it. Your immune system doesn't really work unless it's exposed to the right biodiversity of microbes in your daily world. But we've not build a system for thinking about how do we keep those things around.

Dunn on why most species in homes have been overlooked for so long:

The people who study homes are mostly people whose job it is to kill things. So how do you kill these pests, how do you kill these pathogens? And ecologists like me, we were told to go to the Galapagos, go to the rainforest, go to a deep sea vent and study what's there. And it meant there wasn't anybody to look under your bed. And so when we look under beds, we find new species of insects of spiders, of bacteria, of fungi. More species of fungi have been found in our studies in houses than there are named species of fungi in North America.

More species of fungi have been found in our studies in houses than there are named species of fungi in North America. - Rob Dunn

On why hand washing works:

Well it looks like what happens when you wash your hands with soap and water is that you're washing off the most recently-arrived bacteria species. And the soap and water doesn't disrupt that layer of good bacteria on your skin. And so here's a really simple [example]: You go to the bathroom. You shake somebody's hand, maybe you get a fecal microbe. Well, if you wash your hands with soap and water, that most of the time gets rid of that microbe and leaves your good microbe — that shimmering wonderous diversity — intact.


Amanda Magnus is the executive producer of Embodied, a weekly radio show and podcast about sex, relationships and health. She has also worked on other WUNC shows including Tested and CREEP.
Longtime NPR correspondent Frank Stasio was named permanent host of The State of Things in June 2006. A native of Buffalo, Frank has been in radio since the age of 19. He began his public radio career at WOI in Ames, Iowa, where he was a magazine show anchor and the station's News Director.
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