NEW YORK -- Wash your hands -- it's something officials across the Tri-State Area and the world have said dozens of times to help prevent the spread of the COVID-19 novel coronavirus.
Seven On Your Side Investigates used a black light to see firsthand how washing your hands can make a big difference in whether they're clean or not.
"If you can reduce the amount of germs on your hands, you'll protect yourself and your family from getting exposed to more germs," registered nurse and infection preventionist Barbara Smith said.
Smith, of Mount Sinai Morningside, used a special invisible lotion that simulates germs and a black light to demonstrate how hands should be properly washed.
When putting the lotion on your hands, they appear clean. However, using the black light, it shows they're covered in fake germs.
After washing your hands for 10 seconds, many of the fake germs were still visible under the black light. After 20 seconds of heavy scrubbing, however, all of the germs had disappeared under the black light.
"After 20 seconds, your hands were almost completely clean," Smith said. "We didn't see any more germs."
WATCH: A doctor explains how to properly wash your hands
She also recommends drying your hands completely after washing and using the towel to turn off the faucet.
"The germs are easier to travel from one person to the next if my hands are wet," she said. "So the germs like wetness."
Smith recommends using soap and water to wash your hands thoroughly for at least 20 seconds, which the CDC also recommends.
If you don't have access to soap and water, experts say use hand sanitizer that has at least 60% alcohol.