What  is  the  best  way  to  wash  your  hands?

This exercise is a useful learning tool for explaining the importance of hand washing and using the scientific method to determine how to get the best result.  Your students will learn about experimental technique as well as how to wash their hands effectively.

Before you start:

  • Introduce terms such as bacteria, viruses, microorganisms, pathogens, infection.

  • Discuss the role of pathogenic microorganisms in the spread of human diseases.

  • Describe conditions that harbour bacteria such as warmth, moisture and nutrients.

  • Ask the class about the presence of bacteria on humans:

    • mouth

    • nose

    • ears

    • respiratory tract

    • intestines

    • skin

  • List ways in which bacteria can spread from one person to another.

Practical Hand Washing:

The "Scientific Method" can be used to work out the best way to wash your hands.  A suggested approach is as follows:

Propose Hypothesis

An hypothesis is like an informed prediction of what will happen.  For example, "Washing with soap cleans your hands more effectively than washing without soap".  The good thing about hypotheses is that they can be tested by experiment.  Propose several hypotheses relating to effective handwashing.  Variables you might consider could include:

  • soap

  • water temperature

  • mechanical action (scrubbing)

  • duration (time of washing)

Conduct Experiments

  1. Arrange students in groups of 3 as follows:

Student A = the scribe - collect and record results

Student B = control - provides a basis for comparison

Student C = variable - tests the hypothesis

  1. Have Students B and C apply GlitterBug Potion to their hands.

  2. Have Student A examine the others' hands using a UV light to confirm the presence of the simulated bacteria.

  3. Have Student B wash his or her hands using the agreed control conditions.  For example, you might select the following control conditions when testing the effectiveness of soap:

  • warm running water (approx 40oC)

  • 20 seconds immersion time

  • gentle rubbing action

  • no soap used

  • dry with paper towelling.

  1. Have student C wash his or her hands using the agreed control conditions with the introduction of the variable being tested, eg soap.

  2. Have Student A use the UV light to re-examine the hands and rate the effect of the variable being tested.

Questions

  • Which hypotheses were correct?

  • Were there any big surprises?

  • Can you rank the variables in terms of their effectiveness?

  • Are there ways to overcome the absence of an important factor?  For example, if you have to wash without soap, can you get a good result by washing for a longer time or with more vigorous scrubbing?

Notes

  1. It can help the scribes if they devise a numerical rating system.  For example,

0 = no evidence of GlitterBug under UV light

1 = some signs of GlitterBug, eg around nails and skin creases

2 = patches of GlitterBug can be readily seen

3 = obvious signs of GlitterBug with some clean areas

4 = complete cover of all skin surfaces with GlitterBug

  1. Draw a series of five hands on a large sheet and use shading to indicate degrees of "contamination".  Number each hand according to your agreed rating system.  The scribes in each group can compare their members' hands to the diagrams to help them assign a rating.

  2. Some variables that you test might show only a slight effect.  This can be an opportunity to introduce statistics to help reveal the significance of a weak effect.

  3. List the sources of error that could have influenced the results.  Discuss ways to minimise their effect.