Quick, which if the following factors plays the most important role in effective hand washing:
- water temperature
- the amount of soap used
- time spent washing hands
If you guessed “time spent washing hands”, you are correct. The other two factors had no impact on the amount of bacteria left on a person’s hands after washing their hands.
These results are based on a study conducted at Rutgers University. The researchers found that the study participants had less bacteria after a 10-second lather compared to a 5-second soaping, and hand bacteria decreased even further when they washed their hands for 20 seconds—which is in line with what the US Centers for Disease Control currently recommends (they say to sing “Happy Birthday” twice while you lather).
I would have been curious if one of the test conditions had been “no soap used” to see if soap made any difference at all in how clean a person’s hands are after washing their hands.
One repercussion from the study is that perhaps the FDA should no longer recommend a certain temperature, since it appears that the only effect of using higher water temperatures when washing your hands is a higher monthly utility bill.