Caught Dirty-handed - Experiment

When was the last time you washed your hands? Did you use soap? What have you done since you washed? Have you eaten, put your fingers in your mouth or touched someone else?

Observations in public restrooms have revealed that only about 68 percent of Americans wash up before leaving. Yet thorough hand washing is one of the best ways to prevent the spread of infections. There are millions of microbes on your hands. Most are naturally occurring and harmless. But some may be disease-causing germs. Hand washing with soap lifts off those microbes and rinses them away.

In this group activity, you and your friends or family members will test the effectiveness of different hand washing times, techniques and materials. Print out these pages and start scrubbing. Come back when you're done with the steps to test your newfound knowledge by answering the questions at the end of the experiment. (No fair peeking at the answers before you've done the activity!)

Note: You can do this whole experiment in one to two hours, depending on how many people take part.

You’ll Need:

  • apron or smock for each person (or just wear old clothes)
  • timer or watch that counts seconds
  • sink
  • blindfold
  • 1 tube of washable paint
  • towels
  • soap
  • newspaper

What To Do:

fourhands1. Come up with scoring guide for hand cleanliness. Divide a piece of paper into four sections and trace an outline of a hand in each section. Use your pens or crayons to shade in your idea of completely dirty, very dirty, dirty and slightly dirty. Label the completely dirty hand as ++++, the very dirty hand as +++ and so on. Note that – stands for completely clean.

bluehand2. Cover your workspace with newspaper. Pick one person to be the hand washer and one person to be the timekeeper. The washer should put about one teaspoon of washable paint on the palm of one hand and spread it evenly over both hands, including the backs of the hands and the skin next to and under the fingernails. Allow hands to dry completely—about a minute or two. Close the paint.

3. Go to the sink where hand washer is blindfolded so the washer can’t see his/her hands. Turn on warm water. Have the washer wash with just water for one second. After one second, have the timekeeper blot dry the washer’s hands by very lightly touching the towel to the skin (don’t rub!). Don’t let the hand washer see his/her hands or give away any hints about how clean they are. Using the scoring guide you’ve created, record the cleanliness on a scoring chart. (See sample scoring chart below. This scoring chart should be labeled "Water Only")

4. Have the washer wash for four more seconds with just water. Again, lightly blot the washer’s hands and record their cleanliness.

blueglove5. Have the washer wash for fifteen seconds more with water. Once again, blot and record the cleanliness.

6. Take the blindfold off and allow the washer to completely clean his/her hands. Put the blindfold back on and repeat steps 2 through 5, only this time have the washer use soap each time. Use a new scoring chart labeled "Water and Soap."

7. Change roles and repeat the activity until everyone taking part has had a turn being the handwasher. As much as possible, have the same person keep time and record cleanliness for each hand washer.

8. Display your results. Create two graphs showing the average cleanliness score at each time interval. One graph will show the results when handwashers used water only. The other graph will show results when they used water and soap. Put the time on horizontal line going across the page. Mark every number between 0 and 20 seconds. Put the average cleanliness scores on the vertical line.

caught dirty handed chart


  1. How might hand washing affect your family’s health? Answer
  2. What difference does soap make? Answer
  3. What infectious diseases could be spread by failure of people to adequately wash their hands? Answer

This experiment is based on an activity developed by the National Association of Biology Teachers.


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