Should You Close the Toilet Lid Before Flushing?

Closing the toilet lid before flushing does not completely block aerosols, but it may reduce the amount of airborne particles that travel directly into the breathing zone, according to a new study.

When a toilet flushes, high-speed water strikes surfaces inside the bowl, creating turbulence and tiny droplets that can enter the air. Those particles may contain microorganisms from the water or human waste. Earlier studies found that toilet aerosols can rise to the height of an adult's breathing zone, raising concerns about exposure to microorganisms associated with illnesses including flu and norovirus.

Researchers led by Australia's Flinders University reviewed 22 earlier studies covering different toilets and flushing systems, including seated toilets and some squat toilets. The available evidence was not sufficient to show that closing the lid reduces the total amount of aerosol generated.

The lid's position nevertheless appeared to affect where the particles traveled. With the lid open, aerosols tended to spread into the surrounding environment. With it closed, they could be redirected through gaps between the lid, seat and bowl. Closing the lid therefore does not eliminate aerosols, but may reduce the amount directed toward the breathing zone.

The researchers said bathroom ventilation could also help limit aerosols, although the evidence remains too weak for a firm conclusion. Using a lower water volume on dual-flush toilets when appropriate may reduce aerosol production, while regular cleaning and maintenance can reduce the amount of microorganisms present in the bowl. The study was published in Science of The Total Environment and called for additional design and engineering solutions, particularly in higher-risk settings such as hospitals.