You clean your shoes every time you step on mud or something dirty, but when you get home, do you always take your shoes off outside the door? Not many Australians do this. Usually people do not even think about what they are bringing inside their house with their shoes. We are environmental chemists who have spent a decade investigating the indoor environment and what contaminants people encounter in their homes. Although our examination of the indoor environment, through our DustSafe program, is not yet complete, the question of whether or not a shoe should be taken outdoors is science advocates taking off the shoe outdoors.
It’s best to leave your mess outside the door.
What contaminants are in your home and how did they get there? People spend 90% of their time indoors, so the question of whether or not to wear shoes at home is not a trivial one. The main focus of policy is generally on soil, air quality and the external environment for environmental public health risks. However, there is also increasing regulatory interest in indoor air quality. The substances that are accumulating inside your home are not just dust and dirt brought in by people and hair or skin from pet dander. About a third of it comes from outside, which is either blown into the house with the wind and or enters the house with your shoes. Some microorganisms present on shoes and floors are drug-resistant pathogens, including hospital-associated infectious agents (germs) that are very difficult to treat. Asphalt road residue and chemicals used in lawns contain cancer-causing toxins, which can give you a whole new picture of the dirt on your shoes. Our work involves the measurement and assessment of exposure to a range of harmful substances found inside homes such as:
Antibiotic-resistant genes (genes that make bacteria resistant to antibiotics)
Disinfectant chemicals in the home environment Microplastics Perfluorinated chemicals (known as PFAS or “permanent chemicals”) used everywhere in industrial, household and food packaging products, because they are perpetually in the body. lasts and never ends)
A strong focus of our work is assessing the levels of potentially toxic metals (such as arsenic, cadmium and lead) inside homes in 35 countries (including Australia).
These contaminants – and most importantly the dangerous neurotoxin lead – are odorless and colourless. So there’s no way to know if the dangers of lead exposure are only in your soil or your water pipes, or even on your living room floor. Science suggests a very strong connection between the lead inside your home and the soil in your yard. The most likely cause of this connection is dirt from your yard or on your shoes, and on the paws of your beloved pet. A recent Wall Street Journal article argued that at-home shoes aren’t that bad. The authors said that E. coli – dangerous bacteria that grow in the intestines of many mammals, including humans – is so widespread that it is pretty much everywhere. So it’s no surprise that it can also be on the bottom of shoes (96% of the way down to shoes, as mentioned in the article). Let us clarify here that it is good to be science-oriented and stick with the term E. coli, but to put it simply, it is the bacteria associated with feces. Whether it is ours or our pet, it has the potential to make us very ill if we come in contact with it on a large scale.
There is no harm in having a shoe-free home from an environmental health standpoint. Leaving your shoes on the entry mat also releases potentially harmful pathogens there. We all know that prevention is far better than treatment and taking off shoes at the door can be a basic and easy prevention activity for many of us.
—Mark Patrick Taylor, Macquarie University and Gabriel Filipelli, Indiana University Environmental Resilience Institute