Public-health officials across the globe are urging people to wash their hands, calling it one of the best methods to prevent further spread of the new coronavirus.

But decades of research tell a sobering truth: People need to learn a thing or two about personal hygiene.

Many don’t know proper handwashing technique. They do it for too little time, or they don’t do it at all.

Proper handwashing means scrubbing hands with soap and water for at least 20 seconds, according to the Centers for Disease Control and Prevention.

Yet just 5% of people spent more than 15 seconds washing their hands after using the restroom, and 10% didn’t wash their hands at all, in a study of 3,749 college students published in the Journal of Environmental Health in 2013.

How to Wash Your Hands

Step 1: Scrub your palms together in a circular motion

Step 2: Scrub the back of your hands

Step 3: Scrub the inside of your fingers and under your fingernails

Step 4: Scrub between your fingers

Hands are villages to thousands of germs—including bacteria and viruses. All it takes is a friendly handshake to spread respiratory diseases like Covid-19, the disease caused by the new virus. Respiratory droplets from coughs and sneezes can also spread these germs, as can touching surfaces like doorknobs and phones where those droplets may have landed.

“I don’t think we need to panic,” says Elaine Larson, professor emerita of nursing research at the Columbia School of Nursing, who has helped the World Health Organization develop handwashing guidelines. “But we do need to be reminded about basic hygiene.”

The virus’s fate is in your hands—literally—so experts say it’s time to start practicing what science is preaching.

—Use soap. Before applying soap to your hands, run water over them. Soap and water together, with rubbing, is what helps rinse organisms off your hands and down the drain. Don’t worry about removing hand jewelry, Dr. Larson says. Those need to be washed, too.

Soap acts as a surfactant: a substance that helps release bacteria’s grip from your hand when water is added. The study of college students, however, showed only two in three people used soap. The rest just rinsed their hands.

Dr. Larson suggests half a teaspoon of liquid soap is enough, or a glob about the size of a quarter, although bigger hands might need more. Health experts say that too much soap can remove your skin’s natural oils, which have helpful antibacterial properties.

The CDC says studies haven’t shown that soaps with antibacterial ingredients provide any health benefits or remove more germs than plain soaps. All soaps, however, can deactivate a coronavirus so it can no longer infect you.

The new coronavirus, coined SARS-CoV-2, is a spherical structure with spiky proteins attached to a membrane, or envelope, that protects the pathogen’s genetic material. Once it comes into contact with soap, this envelope dissolves, leaving behind a dysfunctional virus.

“The envelope is a machine that allows the virus to sneak into human cells,” says Jonathan Abraham, an assistant professor of microbiology at Harvard Medical School. “Without it, the virus cannot infect you.”

—Scrub all surfaces of your hands. People on average wash their hands for only about six seconds, according to several studies. Twenty seconds is what’s recommended—or, the length of the “Happy Birthday” song sung twice—though it depends on what you touched and how often.

And even 20 seconds “is not helpful if you’re not washing the right places,” Dr. Larson says. “It’s about quality, not quantity.”

The most vulnerable parts of your hands are your fingertips, between your fingers, the backs of your hands and under your nails. Rubbing these surfaces with enough force is critical, health experts say. People who have longer nails should be extra cautious, they add.

Scrubbing too hard or too frequently can damage your skin by making it dry and more susceptible to cracking, Dr. Larson says. Cuts and cracks give germs the perfect spot to set up shop. To avoid skin damage, Dr. Larson recommends using a moisturizer after washing.

Studies have shown that water temperature doesn’t affect how many germs are removed. The CDC says warm or cold water will do, but some experts warn that when water is too hot, it can also damage skin.

After a thorough scrub with soap, remove all suds by rubbing every surface of your hands under running, clean water to ensure that pathogens get washed away, Dr. Abraham says. Leaving some soap behind may also soak up moisture from your hands, leaving them dry and more likely to crack.

—Dry your hands completely. Now it’s time to dry your hands as thoroughly as you can, because moist hands give living organisms a better chance of surviving and spreading to others, Dr. Abraham says.

The CDC says there is not enough data to confirm whether a significant amount of germs are transferred from the faucet knob to your hands. Some experts suggest using a paper towel to turn the water off, while others discourage it because it wastes paper towels.

Automatic blowers and paper towels both dry hands well.

—Use alcohol-based sanitizers in a pinch. If you’re on the go, alcohol-based sanitizers are great alternatives to soap and water. They cannot kill all viruses, like the norovirus, which lacks a dissolvable envelope. But a sanitizer can kill any coronavirus on your hands as long as it’s made up of at least 60% alcohol, health experts say. Plain rubbing alcohol also works, but sanitizers maintain a balance of alcohol and other ingredients to help keep skin healthy and moisturized.

It’s important to use enough sanitizer to cover the entire hand. Dr. Larson suggests half to one teaspoon.

Sanitizer also works only when it’s still wet, so health experts advise against using paper towels to dab your hands. Give the product at least 10 seconds to complete its job, then rub your hands together or let them air-dry.

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Ms. Camero is a reporter for The Wall Street Journal in New York. She can be reached at katie.camero@wsj.com.