Physics study confirms why you need to wash your hands for 20 seconds

Although hand washing has been shown to be effective in preventing the spread of pathogens and diseases, the physics behind it has not been studied. But now a researcher from Hammond Consulting Limited In Cambridge (UK) showing in revista fluid physics A simple model that captures the mechanisms behind the process.

By simulating hand washing, the timetables As particles such as viruses and bacteria are eliminated during the process. The mathematical model operates in two dimensions, representing the hands (rough on small spatial scales) as wavy surfaces, with a thin layer of liquid in between.

Particles are trapped on the rough surfaces of the hand Potential wells. In other words, they are at the bottom of a valley, and in order for them to escape, the energy of the water flow must be high enough to push them up and out of that valley.

The strength of the fluid flowing between the hands depends on the speed of the hands during movement. The stronger flow removes particles more easily. “Basically, flow informs you of the forces that particles exert,” the author explains. Paul Hammond, “So you can calculate how the particles are moving and see if they are eliminated.”

The researcher compares the process of removing the stain from the shirt: the faster the movement, the more likely it will be removed. “If you move your hands very gently, very slowly, the forces from the liquid are not great enough to overcome the force held by the particles,” says Hammond.

In any case, even if the particles are removed, the process is not fast. The usual recommendations of health authorities, such as Centers for Disease Control and Prevention (CDC) for the United States, indicate that at least 20 seconds under the tap.

Hammond’s model results match that time: It takes about 20 seconds of vigorous motion to flush potential viruses and bacteria from the hands.

This model did not take into account the chemical or biological processes that occur when soap is used. However, knowing the mechanisms that actually remove particles from your hands can provide clues to crafting a more effective and environmentally friendly soap.

Hammond, who acknowledges that this study does not reflect all the intricacies of hand-washing, recalls responding to important questions It lays the foundation for future research.

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