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One of the biggest breakthroughs in preventing the spread of illnesses and infections in hospitals was embarrassingly simple: hand washing. In 1846, Hungarian physician Ignaz Semmelweis discovered that hand washing played a vital role in the spread of germs, and the practice soon became mandatory in hospitals. The simple act of scrubbing hands with soap and water literally saved lives.

Getting a kid to wash their hands, however, can be an uphill battle. While it's a common thing kids (don't) do, global perspective on the importance and effectiveness of hand washing has risen since the COVID-19 pandemic. According to a study published by the National Library of Medicine (NLM) in 2023, before the emergence of COVID-19, a survey found that only about 36% of people always washed their hands with soap, 48% sometimes used soap, and an unsettling 16% of respondents said they wash without soap. After COVID-19 emerged, however, more than 72% of respondents reported using soap every time they washed their hands. There's nothing like a pandemic (and perhaps the reality of FAFO) to strike fear into the hearts of those chronic under washers, but in 2019, one teacher did a simple experiment to show her students just how important hand washing is.

"We did a science project in class this last month as flu season was starting," teacher Dayna Robertson and classroom behavioral specialist Jaralee Metcalf wrote on Facebook. "We took fresh bread and touched it. We did one slice untouched. One with unwashed hands. One with hand sanitizer. One with washed hands with warm water and soap. Then we decided to rub a piece on all our classroom Chromebooks." Robertson later noted that they normally do make a point to sanitize the classroom Chromebooks, but didn't that day in the name of science.

Dexters Laboratory What A Fine Day For Science GIFGiphy

The bread was put into plastic bags and the germs were left to fester. The bread that had been touched by unwashed hands and the bread that had touched the Chromebook had the most mold. The bread that had been touched by hands washed with soap and water remained (relatively) good enough to eat.

This experiment has been done before, but Robertson expanded on it by testing the effectiveness of hand sanitizer. The bread that had been touched by hands cleaned with sanitizer also had a fair amount of mold on it, although not as much as the bread touched by unwashed hands.

The bread doesn't lie. Facebook/Jaralee Metcalf

"As somebody who is sick and tired of being sick and tired of being sick and tired," Robertson wrote, "wash your hands! Remind your kids to wash their hands! And hand sanitizer is not an alternative to washing hands!! At all!" It's kind of making us retroactively gag over seeing port-a-potties with hand sanitizer set up in lieu of sinks.

The experiment was prompted by a different science lesson. "We had just finished a science lesson on how leaves break down during winter. The kids were kind of grossed out by the mold, so we decided to run our own version using germs and mold from our own environment," Robertson told Scary Mommy.

Weirdly, the classroom experiment received some criticism. "Lots of people actually DEFENDED not washing their hands!" Robertson told Scary Mommy. "That was shocking! It really was just a simple classroom experiment to teach about mold but we have all learned more about how easily we can spread the germs we can't see."

In the 2019 lens, this lesson being about mold seems simple enough. All of us here in 2025, though, blessed (or cursed) with the experience of the pandemic, know that washing your hands really is as life-saving as Semmelweis proved nearly two centuries ago. Research done in 2020 and published in PubMed showed that individuals who washed their hands consistently were more likely to have lower rates of COVID-19 infection. According to the Centers for Disease Control and Prevention (CDC) in 2024, hand washing also reduces respiratory illness like colds and flu in the general population by 16-21%, and reduces the number of people with diarrheal illnesses by 23-40%.

And to be sure, how we wash our hands is incredibly important. A quick rinse without scrubbing won't do the trick. According to the World Health Organization (WHO), the proper technique for handwashing is to wet your hands, apply soap, and then run your soapy hands under the stream while rotating, rubbing, and scrubbing every inch of your hands for at least 20 seconds. Usually you can hit that mark by singing "Happy Birthday" twice. Then, rinse. When you're done, dry your hands with a clean towel. Check out this demonstration from the CDC:

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The moral of the story is, please, please remember to always wash your hands. It really makes a difference.

This article originally appeared six years ago. It has been updated.