Meet Your Home's Microbes in The Great Indoors

Taylor Wilcox/Unsplash
Taylor Wilcox/Unsplash

This year, you’ve probably been spending more time than you ever expected at home. You might be sharing space with family members, roommates, pets—and an entire universe of microbes. In The Great Indoors: The Surprising Science of How Buildings Shape Our Behavior, Health, and Happiness, science journalist Emily Anthes investigates homes, offices, schools, hospitals, and other places where we live, work, and play. She looks at how the design of our surroundings affects major aspects of our lives, even when we don’t realize it. In this excerpt, she explores the thriving communities of bacteria and fungi with which we share our abodes—and what they reveal about us.

In 2010, microbiologist Noah Fierer made his first foray into the indoor microbial world, cataloging the bacteria present in 12 public restrooms at the University of Colorado Boulder, where he teaches. (Among the findings: The floor and the toilet handles were home to similar kinds of bacteria, suggesting that some bathroom-goers were flushing the toilet with their feet—“a practice well known to germaphobes and those who have had the misfortune of using restrooms that are less than sanitary,” Fierer and his colleagues reported.) The following year, he studied the microbes in residential kitchens and partnered with Rob Dunn to launch the Wild Life of Our Homes project. They began with a small pilot study in North Carolina, recruiting 40 families to run cotton swabs across seven surfaces inside their homes: a countertop, a cutting board, a refrigerator shelf, a pillowcase, a toilet seat, a TV screen, and the trim around an interior doorway.

The homes were crawling with microbial squatters—more than two thousand types, on average. Different locations within the homes formed distinct habitats: kitchens harbored bacteria associated with food, while doorways were covered in species that typically live in leaves and soil. From a microbiological perspective, toilet seats and pillowcases looked strikingly similar; both were dominated by bacteria that typically live on our skin and in our mouths.

Beyond these commonalities, there was a lot of variation among the homes, each of which had its own microbial profile, sheltering a slightly different collection of organisms. But the researchers couldn’t explain why. So Fierer and Dunn launched a second study, asking more than one thousand families living across the United States to swab the dust that had collected on the trim around their interior doorways.

“We focused on that because nobody ever cleans it,” Fierer told me. “Or we don’t clean it very often—maybe you’re an exception.” (I am not.) Because the dust collects over months or years, the duo hoped it would give them the broadest possible look at indoor life, an inventory of the organisms that had floated, crawled, and skittered through the homes over the previous months and years. As Dunn put it: “Each bit of dust is a microhistory of your life.”

Back in the lab, the team analyzed the DNA fragments present in each dust sample, listing every organism that made an appearance. The numbers were staggering. In total, the indoor dust contained DNA from more than 116,000 species of bacteria and 63,000 species of fungi. “The shocker was the diversity of fungi,” Dunn told me. There are fewer than 25,000 species of named fungi in all of North America, which means that our houses could be teeming with organisms that are essentially unknown to science. In fact, when the researchers compared the indoor dust to samples that the volunteers had taken from the trim around an exterior door, they found that there was more microbial diversity inside the homes than outside of them.

Scientific American/Farrar, Straus and Giroux

Some of the species that Fierer and Dunn identified originate outside, hitching rides into our homes on our clothes or drifting in through open windows. (And they may not all be alive by the time they turn up inside; DNA sequencing can identify the organisms that are present in a sample, but it can’t distinguish between living creatures and dead ones.) Other kinds of bacteria actually grow in our homes—in our walls and our pipes, our air conditioning units, and our dishwashers. Some sprout on our houseplants or our food.

And a lot of indoor microbes, it turns out, are living on us. “We’re constantly shedding bacteria from every orifice and body part,” Fierer said. “It’s nothing to be grossed out about. It’s just the way it is.” Our individual microbiomes—the collection of microorganisms that live in and on our bodies—are unique, and we each leave our own microbial signatures on the places we inhabit. In one innovative study, re- searchers tracked three families as they moved into new homes; each family’s distinct blend of microbes colonized its new residence within hours. The scientists—led by Jack Gilbert, a microbial ecologist then at the University of Chicago—could even detect the individual microbial contributions of each family member. “People who spent more time in the kitchen, their microbiome dominated that space,” Gilbert explained. “People who spent more time in the bedroom, their microbiome dominated there. You could start to forensically identify their movement.”

Indeed, the bacteria that turn up inside a home depend enormously on who lives there. Fierer and Dunn found that Lactobacil­lus bacteria, which are a major component of the vaginal microbiome, were most abundant in homes in which women outnumbered men. When men were in the majority, different bacteria thrived: Roseburia, which normally live in the gut, and Corynebacterium and Derma­bacter, which both populate the skin. Corynebacterium is known to occupy the armpit and contribute to body odor. “Maybe it means that men’s houses smell more like armpits,” Dunn ventured. “Microbially, that’s a fair assessment.” The findings may be due to sex differences in skin biology; men tend to have more Corynebacterium on their skin— and to shed more skin microbes into the environment—than women do. (The researchers also acknowledge the possibility that a bachelor pad’s bacterial profile could be the result of “hygiene practices.”) In a subsequent study, Fierer and his colleagues showed that they could accurately predict the sex of the students living in a college dorm room simply by analyzing the bacteria in its dust.

Meanwhile, dogs introduce their own drool and fecal microbes into a home and track soil dwellers in from outside. (Dog owners never seem too bothered when Dunn tells them that Fido is smuggling an entire microbial zoo into their homes. “It’s a pretty fine conversation most of the time,” he told me. On the other hand, he noted, “If I say that every time your neighbor comes over, that he brings over a mix of beneficial microbes and pathogens, it just makes people scrub.”) Cats change a home’s microbial makeup more modestly, perhaps because they are smaller and venture outside less often. Using the dust DNA alone, Fierer and Dunn were able to predict whether a home contained a dog or a cat with roughly 80 to 90 percent accuracy.

While the bacteria in our homes mostly comes from us (and our pets), the fungi are another story. Fungi are much less abundant in our own microbiomes, and our houses are dominated by fungal species that originate outdoors. A home’s fungal signature, Fierer and Dunn found, was largely determined by where it was located. Houses in eastern states had different fungal communities than those in western ones. Ditto homes in humid climates compared with those in dry ones. The geographic correlation was so strong that Fierer and Dunn could use fungal DNA to determine, to within about 150 miles, where a house dust sample originated.

Fierer and Dunn did identify more than 700 kinds of fungi that were more common indoors than out, including a variety of household molds, yeasts, edible mushrooms, and fungi that live on human skin. Homes with basements had different fungi than those without them. And because some species of fungi feed on wood and other building materials, what our homes are made of affects the fungi that live there. “It’s kind of a ‘three pigs’ thing,” Dunn told me. “A stone house feeds different fungi from a wood house from a mud house. Because unlike the bacteria, they’re eating the house.”

 

Some of the microbes that inhabit our homes are known to cause disease. Black mold, which grows in and on our walls, can trigger allergies and respiratory problems. Aspergillus fumigatus, a fungus that can cause lung infections in people with weakened immune systems, lives in our pillows. Legionella pneumophila, a bacterium that causes Legionnaires’ disease, loves indoor plumbing. It nestles inside hot water tanks, cooling towers, and faucets, and spreads through airborne, or aerosolized, droplets of water. Streptococcus bacteria—which can cause strep throat, sinus and ear infections, pinkeye, meningitis, and pneumonia—are more abundant inside our homes than outside them, Fierer and Dunn found. Though the mere presence of these microbes isn’t necessarily dangerous, and not all strains cause illness, buildings can provide an infrastructure that helps diseases spread. Airborne influenza can waft through an office building’s ventilation system; a spray of Strepto­coccus can turn a doorknob into a booby trap.

But many indoor microbes are completely innocuous, and some may even have lifelong health benefits. In recent decades, the rates of asthma, allergies, and autoimmune diseases have skyrocketed in industrialized nations. Some scientists have theorized that the increasing prevalence of these diseases may be the fault of our modern lifestyles, which keep us at a distance from the robust microbial menageries that surrounded our ancestors for most of human evolution. As a result, our immune systems never get properly trained.

Evidence has been accumulating to support this theory. Studies show that children who live with dogs, which increase the richness and diversity of bacteria in a home, are less sensitive to allergens and less likely to develop asthma. (A dog might be the immune system’s best friend.) Children who grow up on farms, and are exposed to livestock and their microbes, appear to be similarly protected from allergies and asthma.

Some of the most compelling evidence comes from research on two American farming communities: the Amish and the Hutterites. Although the groups have much in common—including large families and Central European ancestry—just 5 percent of Amish kids have asthma, compared to 21 percent of Hutterite children. The communities also have distinct farming customs. The Amish, who generally eschew electricity, live on single-family farms and employ traditional agricultural methods, using horses to plow their fields. It’s not uncommon for Amish children to play in the family barns, which are typically located near their homes. The Hutterites, on the other hand, live together on big, industrial farms, complete with high-tech tools and equipment, and their children have less contact with livestock.

These differences may affect the children’s microbial exposures and the development of their immune systems. In 2016, scientists reported that house dust collected from Amish households had higher levels of endotoxins—molecules contained in the cellular membranes of some bacteria—than dust from Hutterite homes. What’s more, when they drew blood from kids in both communities, they found that compared to Hutterite children, Amish children had more neutrophils, white blood cells that help the body fight infection, and fewer eosinophils, which play a critical role in allergic reactions.

The researchers also whipped up some house-dust cocktails, mixing dust samples from Amish and Hutterite homes with water, and then shooting the slurries into the nasal passages of young mice. Then they exposed the mice to allergens. The mice that had received the Hutterite dust responded as expected; their airways trembled and twitched. But the mice that had received the Amish dust continued to breathe relatively freely, seemingly protected from this allergic response.

Although there’s still a lot to learn, the science suggests that a healthy home is one that’s full of uninvited guests. “We are exposed to microbes every day, and a lot of these are harmless or potentially beneficial,” Fierer told me. “We don’t want a sterile house.” Which is good, because it turns out that I don’t have one.

10 of the Best Indoor and Outdoor Heaters on Amazon

Mr. Heater/Amazon
Mr. Heater/Amazon

With the colder months just around the corner, you might want to start thinking about investing in an indoor or outdoor heater. Indoor heaters not only provide a boost of heat for drafty spaces, but they can also be a money-saver, allowing you to actively control the heat based on the rooms you’re using. Outdoor heaters, meanwhile, can help you take advantage of cold-weather activities like camping or tailgating without having to call it quits because your extremities have gone numb. Check out this list of some of Amazon’s highest-rated indoor and outdoor heaters so you can spend less time shivering this winter and more time enjoying what the season has to offer.

Indoor Heaters

1. Lasko Ceramic Portable Heater; $20

Lasko/Amazon

This 1500-watt heater from Lasko may only be nine inches tall, but it can heat up to 300 square feet of space. With 11 temperature settings and three quiet settings—for high heat, low heat, and fan only—it’s a dynamic powerhouse that’ll keep you toasty all season long.

Buy it: Amazon

2. Alrocket Oscillating Space Heater; $25

Alrocket/Amazon

Alrocket’s oscillating space heater is an excellent addition to any desk or nightstand. Using energy-saving ceramic technology, this heater is made of fire-resistant material, and its special “tip-over” safety feature forces it to turn off if it falls over (making it a reliable choice for homes with kids or pets). It’s extremely quiet, too—at only 45 dB, it’s just a touch louder than a whisper. According to one reviewer, this an ideal option for a “very quiet but powerful” heater.

Buy it: Amazon

3. De’Longhi Oil-Filled Radiator Space Heather; $79

De’Longhi/Amazon

If you prefer a space heater with a more old-fashioned vibe, this radiator heater from De’Longhi gives you 2020 technology with a vintage feel. De’Longhi’s heater automatically turns itself on when the temperatures drops below 44°F, and it will also automatically turn itself off if it starts to overheat. Another smart safety feature? The oil system is permanently sealed, so you won’t have to worry about accidental spills.

Buy it: Amazon

4. Aikoper Ceramic Tower Heater; $70

Aikoper/Amazon

Whether your room needs a little extra warmth or its own heat source, Aikoper’s incredibly precise space heater has got you covered. With a range of 40-95°F, it adjusts by one-degree intervals, giving you the specific level of heat you want. It also has an option for running on an eight-hour timer, ensuring that it will only run when you need it.

Buy it: Amazon

5. Isiler Space Heater; $37

Isiler/Amazon

For a space heater that adds a fun pop of color to any room, check out this yellow unit from Isiler. Made from fire-resistant ceramic, Isiler’s heater can start warming up a space within seconds. It’s positioned on a triangular stand that creates an optimal angle for hot air to start circulating, rendering it so effective that, as one reviewer put it, “This heater needs to say ‘mighty’ in its description.”

Buy it: Amazon

Outdoor Heaters

6. Mr. Heater Portable Buddy; $104

Mr. Heater/Amazon

Make outdoor activities like camping and grilling last longer with Mr. Heater’s indoor/outdoor portable heater. This heater can connect to a propane tank or to a disposable cylinder, allowing you to keep it in one place or take it on the go. With such a versatile range of uses, this heater will—true to its name—become your best buddy when the temperature starts to drop.

Buy it: Amazon

7. Hiland Pyramid Patio Propane Heater; Various

Hiland/Amazon

The cold’s got nothing on this powerful outdoor heater. Hiland’s patio heater has a whopping 40,000 BTU output, which runs for eight to 10 hours on high heat. Simply open the heater’s bottom door to insert a propane tank, power it on, and sit back to let it warm up your backyard. The bright, contained flame from the propane doubles as an outdoor light.

Buy it: Amazon

8. Solo Stove Bonfire Pit; $345

Solo Stove/Amazon

This one is a slight cheat since it’s a bonfire pit and not a traditional outdoor heater, but the Solo Stove has a 4.7-star rating on Amazon for a reason. Everything about this portable fire pit is meticulously crafted to maximize airflow while it's lit, from its double-wall construction to its bottom air vents. These features all work together to help the logs burn more completely while emitting far less smoke than other pits. It’s the best choice for anyone who wants both warmth and ambiance on their patio.

Buy it: Amazon

9. Dr. Infrared Garage Shop Heater; $119

Dr. Infrared/Amazon

You’ll be able to use your garage or basement workshop all season long with this durable heater from Dr. Infrared. It’s unique in that it includes a built-in fan to keep warm air flowing—something that’s especially handy if you need to work without wearing gloves. The fan is overlaid with heat and finger-protectant grills, keeping you safe while it’s powered on.

Buy it: Amazon

10. Mr. Heater 540 Degree Tank Top; $86

Mr. Heater/Amazon

Mr. Heater’s clever propane tank top automatically connects to its fuel source, saving you from having to bring any extra attachments with you on the road. With three heat settings that can get up to 45,000 BTU, the top can rotate 360 degrees to give you the perfect angle of heat you need to stay cozy. According to a reviewer, for a no-fuss outdoor heater, “This baby is super easy to light, comes fully assembled … and man, does it put out the heat.”

Buy it: Amazon

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Action Park: New Book Goes Inside America's Most Dangerous Amusement Park

Photo courtesy Andy Mulvihill
Photo courtesy Andy Mulvihill

In the late 1970s, ski resort owner Gene Mulvihill transformed a mountain in rural Vernon, New Jersey, into a destination for thrill-seekers in the summer months. The result was Action Park, a one-of-a-kind amusement destination that left guests in charge of their own fun. In this exclusive excerpt from Action Park, new from Penguin Books, his teenage son Andy begins to realize that his father’s insistence on autonomy carries with it a measure of risk.

Emboldened by the success of the Lola race cars and their propensity to facilitate legal drunk driving in New Jersey, my father became preoccupied with growing out the entire motorized area of the park. If it needed fuel, it belonged here. He collected things that went fast and faster still, scooping up anything that could accelerate and filling up virtually every corner of the dedicated property with vehicles that guests could race or wreck.

From across Route 94, my ears partially obscured by the helmet worn while patrolling the skateboard park, I could hear the chants: “Wreck the boats! Wreck the boats!”

On a break, I walked across the road and stood out in the rain next to my older brother, Pete. We watched as people zipped around in speedboats that were roughly two-thirds the size of a full-scale version. Powerful engines that seemed way out of proportion for their flimsy plastic frames weighed them down. They populated a mucky-looking lake in Motor World with a small island in the middle.

“Why are they upset?” I asked.

“When it rains, we close down all the motorized rides except for the boats,” Pete said. “The lines get long. They get pissed and start to revolt.” Once someone got in a boat, he said, it was almost impossible to get them out until they ran out of gas.

The boats made a zipping sound as they looped around the island, noses pointed up in the air as if driven by junior cartel smugglers on the run from the Coast Guard. Two teenagers sped directly at each other, hair blowing back, bearing down on the throttle.

“Don’t do that!” Pete yelled. “Don’t you do that!”

The hulls collided with a thonk noise. Both speedboats began to capsize, spilling the occupants into the water.

“Serves them right,” Pete said.

One of them managed to get back into the boat and began cycling around the island again as Erin, the area’s traffic cop, tried to wave him in. The other climbed back on the dock, dripping with water and reeking of gasoline.

“There’s fuel all over my shorts!” he shouted. “My skin is burning, man!”

“Go to the office,” Pete said. “They have soap.”

Fuel and engine oil leaked from the motors, giving the entire lake a greasy sheen, like the top of a pizza. People who had been tossed into the water often started screaming. “Something brushed against my leg!” they would wail as they waded toward land, looking back as though a shark might emerge from the four-foot depths.

“Snakes,” Pete said. “Some of them are copperheads. We have snapping turtles, too. They can take a toe.” Doing laps in the boats first thing in the morning, Pete said, usually scared them off.

The relative sophistication of the motor-powered rides didn’t prevent us from installing low-cost attractions as well. Adjacent to the speedboat lake was a giant pile of hay bales that stretched more than ten feet in the air. They formed a winding labyrinth that resembled an obstacle course constructed for a rat in a laboratory. A sign next to it read: Human Maze.

A buddy of mine from school, Artie Williams, worked as the maze attendant. He was a good tennis player and read The New York Times every day without fail. These would normally be insufferable qualities for a teenager, but Artie managed to remain likable. He said he often heard muffled pleas for help from inside the maze. “People don’t understand it’s actually complicated and hard to get out of,” he said. “They think it’s like one of those things you draw a line through in a puzzle book. I wouldn’t go in without a rope tied around my waist.”

Snakes occasionally made their way into the bales, he said, popping out and causing people to sprint away in a mad panic, getting themselves even more lost than before. In the middle of summer, the bales also trapped heat, effectively turning the maze into a suffocating furnace. People emerged from the exit soaked in sweat and gasping. “Water, water,” they whispered, dry lips cracking. One of these disappearances actually made the local newspaper.

After a week, I saw a sign go up near the entrance:

DANGER

People Have Been Lost in This Maze for Up to 9 Hours

“It’s good to warn them up front,” Artie said, The New York Times tucked under his armpit.

As Motor World swelled, so did the rest of the park. New attractions seemed to erupt from the ground weekly, and other areas found new purpose. My father put in batting cages and basketball courts. The ski lift became the Sky Ride, a “scenic, 40-minute tour through the mountain landscape.” Trails of pot smoke surrounded the lifts. The race car mechanic, Mike Kramer, had cobbled together single-occupancy tanks that shot tennis balls at velocity at both guests and employees. It was Wimbledon meets Vietnam.

The concept of the Vernon Valley Fun Farm was already too quaint. The park was evolving, reflecting the increasingly rabid tastes of its patrons. The diesel-drenched success of Motor World and the failure of the comparatively serene skateboard park proved that people wanted speed and danger, competition and risk.

They did not want a fun farm. They wanted an action park.

Penguin Books

Excerpted from Action Park: Fast Times, Wild Rides, and the Untold Story of America’s Most Dangerous Amusement Park by Andy Mulvihill with Mental Floss senior writer Jake Rossen. Published by Penguin Books, an imprint of Penguin Publishing Group, a division of Penguin Random House, LLC. Copyright © 2020 by Andrew J. Mulvihill.