On the bus, a man is picking his nose. A child is touching every surface with grimy fingers and half of the passengers are coughing onto their neighbors. This seems like an outbreak waiting to happen.

But, there’s one simple way to cut the odds of getting sick after a scene like this — and it works for the flu, a cold, e-coli, norovirus, rotavirus or even coronavirus.

What is this magical solution? hand-washing.

Can soap kill coronavirus?

“Hand-washing is the second best way to prevent getting an infection,” Dr. Dan McGee, a pediatrician at Helen DeVos Children’s Hospital in Grand Rapids, Michigan, told TODAY. “The first best way is if you get a vaccine — if one is available.”

Is it really enough? Trevor Noah was pretty skeptical during his “Daily Show” monologue.

“Science is always warning us of some new weird death virus and when we’re like, ‘What’s the plan?’ They’re like, ‘Ahh wash your hands.’ That’s not a plan!” he said, adding that rigorous hand-washing never halts a zombie apocalypse in movies.

But, it’s actually been proven by science. A large new study published in the Cochrane Database of Systematic Reviews reinforced that hand-washing helps slow the spread of illness. In fact, it reduced the chances of contracting a respiratory illness by 54% — the best odds of any other option.

This isn't surprising. hand-washing became known as a major way to slow the spread of infections way back in the 1850s when Louis Pasteur and Joseph Lister documented what a huge difference it made. (Though they weren’t the first to notice: Ignaz Semmelweis realized that hand-washing saved lives 20 years earlier. Sadly, clean hands didn’t become popular until after his death.)

“It was a rather radical concept and people thought it was crazy,” McGee said.

How should you wash your hands?

So what's the proper way to clean hands? It involves more than a splash of water and a pat dry on a hand towel. Experts recommend that people wash their hands for a full 20 seconds to clean off bacteria. They suggest tracking the time by singing. Most people recommend “Happy Birthday” or the alphabet song for children, but McGee said any song will do.

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“There's probably a few other drunken sailor songs you can sing, too,” he said. “But, it’s just making sure that you spend enough time washing.”

In fact, people already exhausted of humming (or belting out) "Happy Birthday" shared new song recommendations on social media. A picture on Facebook listed a few suggested tunes with choruses that last 20 seconds, including "Good as Hell" by Lizzo and "Africa" by Toto (sung twice).

Dr. Mehmet Oz showed Carson Daly how to properly wash hands and stressed the importance of keeping fingertips clean.

"What will touch our face is our index finger or our thumb," he explained.

He also recommended a little back and forth rubbing and twisting action with the fingers intertwined and then a twist-cleaning of thumb separately.

"Washing your hands is about getting your fingers wet," he said. "Once you get the soap on your hands, don’t just wash the back of your wrists, no one cares. It’s your fingertips that matter."

Finally, he recommends cleaning the palms.

"Grease the palms," he said. "You have 20 seconds to meditate on life. Don’t think about just staying calm. Realize we are a 'can do' nation. We can stay ahead of this we just give the healthcare system a little bit of time."

Does hot water kill coronavirus?

McGee recommends using warm water and soap, though the temperature of the water doesn’t matter that much when it comes to eliminating germs.

“For hot water itself to kill a germ it would have to be boiling,” McGee explained. “Warmer water helps the soap to disperse better. But, temperature really is not a factor in killing off the bacteria.”

Does antibacterial soap kill coronavirus?

Some people think antibacterial soap is better, but using it all the time can backfire. McGee warns against relying too heavily on it.

“If everybody's using antibacterial soaps, you're going to actually encourage drug-resistant bacteria to develop,” he said. “Any soap and water is good.”

Should you use a towel or air dry?

Drying hands with a paper towel or hand dryer might be slightly better than using a reusable hand towel, which can harbor some dirt and bacteria. But in any case, it’s important to dry the hands thoroughly. Wet hands make a perfect environment for germs to flourish.

“If you're walking around with wet hands,” McGee said, “that's a better culture medium for infection.”

How often should you wash your hands?

When is it time to wash hands? This can seem confusing, but some of it is just instinct.

“The best time to wash your hands is whenever you think you should be washing your hands,” McGee said. “If you're around sick people at all, around children or in public places and you've touched something that other people have touched, then you need to wash your hands.”

Cold and flu viruses last a surprisingly long time on surfaces: between six and eight hours. Something like the norovirus can live for 24 hours on surfaces. That’s one reason why McGee suggests using a paper towel in public bathrooms to grab the door handle — after washing hands.

“You don't know if the person before you washed their hands,” he said.

hand-washing might take a few extra minutes, but it’s an easy and really effective way to slow the spread of illnesses like the flu and coronavirus from one person to another or just from touching a contaminated surface.

“Something as innocent as rubbing your eye can bring a virus in your body,” McGee said. “That's why it's important to keep your hands clean.”