It has been known for years that wearing your shoes indoors means that everything that is on the ground outdoors will be tracked into the home. Pesticides, heavy metals, lead, animal feces, and everything else out there.
Babies crawling around the floor (and also putting things into the mouth) get an extra heavy dose of "contaminants" that were tracked in. We all absorb contaminants through our skin, ingest (the mouth), or breathe them in.
All these contaminants become part of our indoor air quality. Our indoor air is not just the outside contaminants that made their way in, but there is also shedding of skin and cloth fibers from us and pets, as well as outgassing and breakdown (the dust) of whatever is in the home. We can't get rid of all contaminants, but we can really lower our exposure to them by not wearing our shoes indoors.
Bottom line: Take your shoes off at the door.
A nice discussion of this issue is in an article written by Professors M.P. Taylor and G. Filippelli earlier this year. Some excerpts from The Conversation: Wearing shoes in the house is just plain gross. The verdict from scientists who study indoor contaminants
You probably clean your shoes if you step in something muddy or disgusting (please pick up after your dog!). But when you get home, do you always de-shoe at the door?
Plenty of Australians don’t. For many, what you drag in on the bottom of your shoes is the last thing on the mind as one gets home.
We are environmental chemists who have spent a decade examining the indoor environment and the contaminants people are exposed to in their own homes. Although our examination of the indoor environment, via our DustSafe program, is far from complete, on the question of whether to shoe or de-shoe in the home, the science leans toward the latter.
It is best to leave your filth outside the door.
People spend up to 90% of their time indoors, so the question of whether or not to wear shoes in the house is not a trivial one.
The matter building up inside your home includes not just dust and dirt from people and pets shedding hair and skin. About a third of it is from outside, either blown in or tramped in on those offensive shoe bottoms.
Some of the microorganisms present on shoes and floors are drug-resistant pathogens, including hospital-associated infectious agents (germs) that are very difficult to treat.
Our work has involved the measurement and assessment of exposure to a range of harmful substances found inside homes including: antibiotic-resistant genes (genes that make bacteria resistant to antibiotics), disinfectant chemicals in the home environment, microplastics, the perfluorinated chemicals (also known as PFAS or “forever chemicals” because of their tendency to remain in the body and not break down) used ubiquitously in a multitude of industrial, domestic and food packaging products, radioactive elements.
A strong focus of our work has involved assessing levels of potentially toxic metals (such as arsenic, cadmium and lead) inside homes across 35 nations (including Australia).
These contaminants – and most importantly the dangerous neurotoxin lead – are odourless and colourless. So there is no way of knowing whether the dangers of lead exposure are only in your soils or your water pipes, or if they are also on your living room floor.
The science suggests a very strong connection between the lead inside your home and that in your yard soil. The most likely reason for this connection is dirt blown in from your yard or trodden in on your shoes, and on the furry paws of your adorable pets.