I learned this from a microbiology podcast at two in the morning and I have not been able to unlearn it. When you flush a toilet with the lid up, you are launching a plume of microscopic droplets into the air. Those droplets contain whatever was in the toilet — and they land on your toothbrush, your towel, your hair products, everything within a six-foot radius.

There is a term for it: toilet plume. Researchers at the University of Colorado Boulder used lasers to visualize what happens when you flush. It is not subtle. Particles shoot several feet into the air and hang there for minutes. Some settle on surfaces. Some you breathe in.

The evidence is not new

A 1975 study by Charles Gerba — who is known as “Dr. Germ” in microbiology circles, a title that must make dinner parties awkward — showed that bacteria and viruses from toilet flushes spread to bathroom surfaces and stay viable for hours. More recent studies have confirmed the same thing with better equipment. The plume contains E. coli, norovirus, and whatever else was in the bowl.

The simplest fix ever

Close the lid. Then flush. That is it. The lid blocks the plume almost completely. No droplets, no spread, no toothbrush contamination.

This is genuinely the easiest habit to build. There is already a lid. You are already standing right there. The only thing that changes is flipping it down before you press the handle instead of after. Give it two weeks and it becomes automatic.

What if you cannot close the lid

• Public restrooms: Most do not have lids. Flush and step back immediately. Keep your mouth closed for a few seconds — yes, really.
• Store your toothbrush in a cabinet or drawer. If you leave it out on the counter, it is in the splash zone.
• Clean bathroom surfaces regularly. The plume settles on counters, faucets, and soap dispensers.

The cleanup bonus

Closing the lid also prevents things from falling into the toilet. Phones, makeup brushes, toddlers’ toys. I do not have stats on how many phones end up in toilets every year but it is not zero. A closed lid solves multiple problems at once.

I told my partner about this after that late-night podcast and now we are both militant about it. The lid goes down before the flush. No exceptions. Our toothbrushes live behind a cabinet door. We have become those people. No regrets.