The habit of walking through the house in shoes worn outdoors is drawing fresh attention as a hygiene issue. As study after study shows that bacteria and chemicals picked up on the soles of shoes can be tracked onto indoor floors, the practice of taking off shoes at the door is spreading in the United States as well.
Time magazine on the 14th reported on research into the bacteria and harmful substances that shoes can carry into the home.
When researchers at the University of Arizona examined 26 pairs of shoes worn outdoors for three months in 2008, they found between 3,600 and as many as 8 million bacterial colonies on the inside and outside of the shoes. The most commonly detected was E. coli, which can originate from feces.
Charles Gerba, a professor of virology at the University of Arizona who led the study, said fecal bacteria were detected on about 80% of shoe soles. "Most of it comes from public restroom floors, but it can also come from outdoors where there are dogs, birds and the like," he said.
Other research has confirmed the potential for contamination through shoes. Researchers at the University of Houston examined shoes and found Clostridioides difficile, which can cause diarrhea, on 40% of them.
Bacteria on Shoes Move to Household Floors
The problem is that bacteria on shoes do not simply stay on the soles. Experiments have also shown that bacteria attached to shoes can move onto indoor floors.
In a 2009 experiment in Alaska, participants wore sterilized boots and walked outdoors. When the boots were later tested, several types of intestinal bacteria were found on 70% of them. When the participants put the contaminated boots back on and walked across sterilized floors, bacteria transferred to the floor in about half of the cases.
The degree of contamination varied with the flooring material, such as carpet, but in each case shoes worn outdoors could serve as a vehicle carrying contaminants indoors. Alessandra Leri, a professor at Northeastern University, said shoe soles are a major vehicle for carrying fecal bacteria from the outside environment into the home.
Bacteria are not the only thing coming into the house. Per- and polyfluoroalkyl substances (PFAS), known as forever chemicals, along with lead dust from older homes and pesticides used on farms or in gardens, can also be tracked indoors on shoes.
According to Gerba, contamination levels inside the home were highest around the entryway. Households with infants and toddlers who crawl on the floor or use their hands on it need to be especially careful about contaminants brought in on shoes, he said.
"Please Take Off Your Shoes": Changing Homes Among Young Americans
As such findings and interest in hygiene grow, taking off shoes inside the home is becoming an increasingly familiar way of life in the United States.
In a 2023 poll by CBS News and YouGov, 63% of Americans said they regularly take off their shoes when they get home. Twenty-four percent said they also ask guests to remove their shoes.
Generational differences were pronounced. Only 7% of those aged 65 and over and 13% of those aged 45 to 64 said they ask guests to take off their shoes, but the figure rose to 44% among those aged 18 to 29. The practice of going shoeless indoors is spreading fastest among young adults.
Health authorities in the U.S. state of Indiana also launched a campaign this year encouraging people to take off their shoes inside the home, with a particular focus on reducing lead brought indoors on shoes from outside.
"It seems many people have already adopted this custom," Leri said, adding that removing shoes is a more hygienic way of life.
