Transcript for Classroom Experiment Reveals Just How Quickly Germs Can Spread
We're now all back in our seats. Nice and calm. Back. And coming up on 7:42 "Gma" on the lookout for germs at school. Dozens of school and staff at a Boston school were home sick with the norovirus. We wanted to see how quickly and easily germs can spread and what you can do to stop them. Paula Faris has that story. ? Reporter: Right here, right here. Right here. Reporter: The discovery is startling. Look at that. Whoa. Reporter: Those bright patches could be germs, and they're all over these kids' faces. But check it out, just a few hours earlier, not a trace. "Gma" on the lookout. Teaming up with these New Jersey fourth graders. Good morning. Reporter: Demonstrating how rapidly germs can spread in a classroom. Are germs good or are germs bad? They're bad. Reporter: We use a harmless powder called glow germ that spreads like a disease. A powder on your hands. Can't see it with your eye, but under a black light. When the lights go off, the germs come out to play. That powder only on two students, Julia and Jonathan. We're going to track it throughout the day and see where it spreads. Doesn't need all day to spread. After one hour, the powder spreads to every single child in the classroom. Right here. Look at that. Some had direct contact with Julia and Jonathan. Your pinky is glowing. Others, indirect contact. I touched her pencil. Reporter: Look at that. A big mark right there. Eventually, it's all over their faces. You have a big fwlglob right there. Do you see it? All long your cheek. You rubbed your nose and your eyelid. Wow. Germs spread in a hurry. Just this week 150 students and staff sick with the norovirus at this Boston school. But prevention it be simple. Don't touch your face. Sneeze into a tissue. And most importantly, wash your hands for 20 seconds. How long do you wash your hands for? Xavier shows what happens when you don't wash long enough. See your wrist? But the best advice of all, when you are sick, come to school or stay home? Stay home. Reporter: Why? Because you don't want to get your classmates sick. Reporter: That's right. That's why you keep them home, and same for the work place. Germs spread in the hurry. It's the indirect contact. Give me a squirt. I don't know if I want that blue light. Wash, wash, wash. We're everywhere. You cannot do it too much. Indirect contact, pens, pencils, everything. Thank you so much. We'll be watching you this weekend. Elbow bump.
This transcript has been automatically generated and may not be 100% accurate.