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How does handwashing help prevent illness? The science of soap.


All Grades

It's true what Robert Fulghum said, "All I really need to know, I learned in kindergarten."

Frequent handwashing is one of the top recommendations from the Centers for Disease Control and Prevention (CDC) amid the coronavirus outbreak. Since early childhood, we've all been taught that keeping our hands clean is one of the most important steps we can take to avoid getting sick and spreading germs to others. Many diseases and conditions are spread by not washing hands with soap and clean, running water.

So, the good news is that by simply washing our hands, we can help decrease the spread of coronavirus and other things that make us sick.

Here are four easy steps to clean hands:

  1. Get wet and soapy. Get your hands wet in clean water. Put soap on your hands and make suds.
  2. Rub. Rub your soapy hands together long enough to sing "Happy Birthday" twice. Or, make it fun by doing the "I Will Survive" Challenge with others showing off their handwashing techniques on TikTok. This will give you time to clean your palms, the back of your hands, and between your fingers. Don't forget to clean under your nails. Nails can trap dirt and germs.
  3. Rinse. Hold your hands under clean, running water. Rub them to rinse them thoroughly.
  4. Shake and dry. Shake your hands a few times, then dry them with a clean towel or hand dryer.

Why does this simple habit of washing our hands with soap and water pack such a powerful blow to nasty germs?

First, soap doesn't kill germs on our hands; it removes them. The basic ingredients of soap are a mixture of fat or oil, water, and an alkali, or basic salt.

Immiscible substances are not mixable

Germs stick to the oils and grease on our hands (sounds gross, but it's normal). Water alone won't remove much of the germs on our hands because water and oil are immiscible chemicals, so they won't mix. But soap likes both water and oil, so it gets them to interact. Soap molecules have one end that's water-loving, or hydrophilic, and another end that's oil-loving, or hydrophobic.

Emulsifiers and surfactants  

Soap cleans by acting as a surfactant and emulsifier. It can surround oil, making it easier to rinse it away with water.

Surfactants lower the surface tension of water, making the molecules slipperier, so they are less likely to stick to themselves and more likely to interact with oil and grease. You may have seen surfactant ingredients such as Sodium lauryl sulfate, sodium laureth sulfate, disodium lauryl sulfosuccinate, or cocoyl sarcosinate.

As an emulsifying agent, soap is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.

When you wash your hands with soap, the soap molecules act as a mediator between the water and oil molecules and bind with both at the same time. Then when you rinse everything off, the soap carries away the germs with the water. So, it's important to work up a lather because the friction helps lift dirt and oils from your skin, according to the CDC. Until you get those hands washed, avoid touching your eyes, nose, and mouth.

To get younger students in the habit, download the “The Ewww Experiment.” This biology activity is sure to make it clear why you should wash your hands before dinner! It’s a quick, easy, and inexpensive way to show young learners what those invisible little organisms all around us can do.

We can all lead by example. Make sure to practice what we preach. When students see the leaders in their schools, wash their hands before eating a meal, after using the bathroom, and after completing a lab, they are more likely to do the same.

To learn more visit the CDC’s Handwashing: Clean Hands Save Lives.


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