Flushing Sends Invisible Germ Clouds Into the Air – And You’re Breathing Them In

Flushing toilets can release bioaerosols carrying bacteria like E. coli and S. aureus, exposing restroom users to potential health risks, including nausea and diarrhea.

A new study found that squat toilets produce significantly more airborne bacteria than bidet toilets, and that flushing with waste present increases contamination levels. However, using exhaust fans can dramatically reduce exposure, highlighting the need for better ventilation in public restrooms.

Hidden Health Risks in Public Restrooms

Toilet flushing releases bioaerosols — tiny `irborne particles that can carry bacteria — posing a potential health risk in public restrooms. A recent study published today (February 17) in the scientific journal Risk Analysis found that flushing significantly increases airborne concentrations of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), often exceeding safety levels set by the Centers for Disease Control (CDC). Inhaling these bacteria can lead to symptoms such as nausea, diarrhea, abdominal cramps, and vomiting.

Comparing Bioaerosol Levels in Different Toilet Types

Researchers conducted the study in two office restrooms in China, one with a squat toilet and the other with a bidet-style toilet. They measured the levels of airborne S. aureus and E. coli under different flushing and ventilation conditions. The results showed that squat toilets released significantly more bacteria into the air — 42% to 62% more S. aureus and 16% to 27% more E. coli — compared to bidet toilets.

In addition, bioaerosol concentrations were 25 to 43 percent (S. aureus) and 16 to 27 percent (E. coli) lower after the first flush of an empty toilet compared to those observed after a second flush (when feces were present).

The Role of Ventilation in Reducing Risk

Importantly, the researchers found that active ventilation with an exhaust fan reduced the risk by 10 times.

“Our findings underscore the substantial health risks posed by bioaerosol exposure in public washrooms,” says lead author Wajid Ali, a PhD student in environmental studies at China University of Geosciences. “Enhancing ventilation systems by optimizing exhaust fan efficiency and air exchange rates can effectively reduce bioaerosol concentrations and exposure risks for the public.”

He adds that the findings for squat toilets apply for seated toilets as well. For public health policymakers, the results of the study provide evidence-based recommendations to define safe bioaerosol exposure limits and promote hygiene practices in public washrooms, ensuring healthier and safer indoor environments.

Reference: “Quantitative microbial risk assessment of bioaerosol emissions from squat and bidet toilets during flushing” by Wajid Ali, Zhen Hu, Zhe-ren Tang, Si-yi Liu, Zaheer Ahmad Nasir, Frederic Coulon, Peng Liu and Cheng Yan, 17 February 2025, Risk Analysis.