The evidence is strong that soles can carry material from outdoors and that transfer to indoor surfaces can occur. It is much weaker when moving from detection of contamination to quantifying clinical risk in everyday domestic life.
Streets, pavements, public transport and shared areas.
Pick up material depending on surface, moisture and route.
A logical point at which to intercept part of that material.
Residual material can be transferred through movement.
What the 2016 systematic review found
The 2016 review identified 13 studies on infectious agents found on shoe soles and 15 studies on decontamination strategies. Relevant microorganisms were documented in healthcare, community and food-worker settings. The authors also concluded that no decontamination strategy had been shown to disinfect shoe soles consistently.
More recent evidence is mainly healthcare-based
A review published in 2024 analysed healthcare or controlled experimental studies and documented recovery of pathogens from floors and footwear. The findings describe dissemination potential in those settings; risk in private homes requires a separate assessment.
Shoe-sole dust can contribute to the indoor airborne microbiome
In a 2024 indoor study, source-apportionment analysis estimated that shoe-sole dust contributed about 4% of airborne bacteria and 14% of airborne fungi measured in that setting. This is evidence of environmental transfer in a specific study, not a universal figure and not direct evidence of health harm.
What we can conclude cautiously
Shoe soles are a physical route through which outdoor material can enter indoor environments, and the threshold is a logical place to intercept part of that load. These sources do not support saying that shoes “make people ill” or that a single entrance intervention eliminates health risk.
Acting where residue enters
Entrance hygiene concerns the outdoor-to-indoor transition: removing shoes where practical, using passive entry systems, cleaning when needed and evaluating dedicated technologies only through real testing. HOME KLINX belongs in this territory, but its specific performance will be communicated only after dedicated validation.
Faeces and urine: residue along the route
When a sole contacts soil or surfaces containing faeces and urine, it can pick up traces along with soil and water. Contact, moisture and the route travelled determine the amount picked up and its subsequent transfer.
Pesticides: measured transfer into homes
Nishioka and colleagues studied 11 occupied and two unoccupied homes before and after the herbicide 2,4-D was applied to lawns. They detected the compound in indoor air and on indoor surfaces. Transport by an active dog and the person who applied the product was among the most significant factors. The study concerns that herbicide and those conditions, not every pesticide or every return home.
Viruses: what detection on soles establishes
In 2020, Guo and colleagues detected SARS-CoV-2 genetic material on staff shoe soles in COVID-19 wards. Measurement used PCR and the authors state that it did not indicate the amount of viable virus. This is evidence of hospital contamination, not a measure of household infection risk through footwear.
Sources & evidence
- Shoe soles as a potential vector for pathogen transmission: a systematic review
- A Review of the Evidence on the Role of Floors and Shoes in the Dissemination of Pathogens
- Height-Resolved Analysis of Indoor Airborne Microbiome
- Nishioka et al., 2001 — 2,4-D in indoor air and on household surfaces
- Guo et al., 2020 — SARS-CoV-2 genetic material in hospital wards