Do You Really Need to Wash Your Hands for 20 Seconds?

For months, public health authorities around the world have been instructing us to wash our hands to prevent the spread of Covid-19. Chances are, you've seen posters specifying 20 seconds as the amount of time you should spend at the sink.

But why 20 seconds? And is it really necessary to spend that long washing your hands? According to new research published last month in the journal Physics of Fluid, the answer to the second question is a resounding "yes." Using mathematical modeling, the researchers determined that 20 seconds is required to dislodge the viral and bacterial particles that are attracted to our hands. Furthermore, moving your hands more vigorously provides the right amount of force to allow particles to escape into the running water.

The Centers for Disease Control (CDC) has long recommended washing your hands with soap and water for 20 seconds, but their recommendation was based on the link between how many microbes remain on your hands and how long you spend washing them. In contrast, this study used physics to examine how much energy is needed to overcome the attractive forces keeping germs on our hands.

Don't forget to wash your hands!