Here's why you should always close the toilet lid when you flush

The average person flushes the toilet five times a day and, apparently, most of us are doing it wrong. Get ready for some hard truths about why you should always leave the lid closed when you flush.

When you pull the lever, in addition to taking whatever business you’ve left behind down into the sewer pipes, your toilet also releases something called “toilet plume” into the air — which is basically a spray filled with microscopic bacteria, including E. coli. According to research from 1975, the germs emitted in the spray can linger in the air for up to six hours, and disperse themselves all over your bathroom … including on your toothbrush, towels and beauty products.

"Contaminated toilets have been clearly shown to produce large droplet and droplet nuclei bioaerosols during flushing, and research suggests that this toilet plume could play an important role in the transmission of infectious diseases for which the pathogen is shed in feces or vomit,” reads a 2015 update on the 1975 study from the "American Journal of Infection Control." "The possible role of toilet plume in airborne transmission of norovirus, SARS and pandemic influenza is of particular interest.”

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Here's why you should always close the toilet lid when you flush

Luckily, today’s toilet technology minimizes the amount of toilet plume that’s shot into the air, but it’s still something about which it's worth being aware. "The bigger droplets and the aerosol likely don’t travel very far above or around the toilet, but very tiny droplets could remain suspended in the air for some time,” microbiologist Dr. Janet Hilltold TODAY Home. "Since the water in the toilet bowl contains bacteria and other microbes from feces, urine and maybe even vomit, there will be some in the water droplets. Every gram of human feces contains billions and billions of bacteria, as well as viruses and even some fungi."

The easiest way to avoid this nastiness coating your bathroom is, simply, to close the toilet seat. "Closing the lid reduces the spread of droplets,” Hill explained. If you’re in a public bathroom where there is no toilet seat to be found, keep as clean as possible by not leaning over the bowl when you flush and washing your hands immediately afterward.

The good news? Even though it’s (really, really) gross, forgetting to put down the toilet seat when you flush likely won’t result in sickness. "The chances of getting an infection from toilet aerosols is really, really low,” said Hill. “The vast majority of microbes in human urine and feces are completely harmless — and actually beneficial. If you were using a toilet that had also been used by someone with a nasty infection, like, say, they had diarrhea from salmonella or campylobacter infection, then the water might contain a very tiny number of these organisms. But in order to actually get infected, you would have to ingest bacteria that were still alive and ingest them in sufficient numbers to cause an infection. Bacteria won’t survive indefinitely in toilet bowls or on toilet surfaces, and getting the bacteria on your skin or clothes doesn’t mean that you will ingest it, and so you wouldn’t get infected.”

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The types of germs associated with intestinal infections — like vomiting or diarrhea — aren’t transmitted via the respiratory tract, so breathing them in is likely no big deal. "If you add up all these factors, the health risks associated with aerosolized toilet water are extremely low,” she said.

In fact, the risks are so low that some don’t scientists consider closing the lid to be entirely necessary. "There is little advantage to closing the toilet lid when you flush,” said microbiologist Dr. Bill Ghiorse. "The few microbes that could harm you are already there. The flushed material will be conducted to the sewers system efficiently leaving little chance for aerosolization, which is the only possible route for infection. You could hold your breath when you flush; but it is much more important to keep the toilet bowl clean and wash your hands after flushing.”

So, if you forget to put down the lid, it's probably no big deal. But why not do it anyway, just in case? As Hill aptly put it, " Toilets have lids for a reason."