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Ohio 4-H Youth Development

Ohio State University Extension

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Mold Science – Learning about Germs (Dirty/Clean Challenge)

Join our 4-H teen as he learns about the importance of washing your hands!

What are we learning today?

You might think your hands are clean, but how clean are they really? Think about all of the things you touch during the day: your phone, computer, or door handles. 

Let's try out an experiment to reveal those germs we can't see.

What do you need? 

  • 5-6 slices of bread (fresh, bakery-style with few preservatives works best)
  • Clear resealable sandwich bags (1 for each slice)
  • Permanent marker
  • Access to things you touch a lot (your hands, phone, door handle, etc.)
  • Notebook or log to track results over time
  • Cool, dry place to store your bags

Try it yourself

  1. Label your bags
    • Use your marker to label one bag each for: 
      • Unwashed hands
      • Washed hands
      • Phone
      • Household surface (like a fridge handle or a bathroom sink)
      • Control (untouched bread)
  2. The tests begin!
    • First – unwashed hands:
      • Touch a slice of bread with your hands before washing them. Get some good fingerprints on it! Then seal it in the "unwashed hands" bag.
    • Next – Washed hands:
      • Wash your hands really well with warm, soapy water for 20 seconds. Then touch a new slice of bread and seal it in the "washed-hands" bag.
    • Then – Phone: 
      • Use another slice to press lightly against your phone screen. Seal it in the "phone" bag.
    • And – A household surface:
      • Rub a slice on something you touch a lot – like the fridge door, a doorknob, or the TV remote. Seal and label it!
    • Finally – our "control":
      • Take one slice of bread and put it in a bag without touching it at all. This is your control to compare how mold grows with and without contact.
  3. The waiting game
    • Place all the sealed bags in a cool, dry area where they won't be moved
    • Then wait and observe
    • Every few days, check the bags and record what you see in your notebook.Moldy bread on a plate
    • You might track:
      • Color changes
      • Mold growth
      • Smell (If you dare – but don't open the bags!)
      • Which slice changes first?
      • Which one stays clean longest?
    • Keep checking for up to four weeks. The more bacteria on your hands or items touched, the faster and more dramatically mold can grow

This experiment shows just how much we spread germs without even noticing. Washing your hands – especially before you eat or cook – is one of the easiest ways to stay healthy

Open and print the supply list for yourself!

Want to learn more?