Curious Kids: why do we need soap?

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Source: The Conversation (Au and NZ) – By Mary-Louise McLaws, Professor of Epidemiology Healthcare Infection and Infectious Diseases Control, UNSW

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.


Why do we need soap? – Claire, age 4.


Thank you, Claire, for your question.

Soap is fun; it feels nice and slippery, you can blow bubbles with it and it often smells lovely. But it also keeps you healthy because it makes it easy for us to remove germs.

Germs are very very small, so small they are invisible to our eyes. We have many germs on our hands all the time. They like to live in the invisible layer of oil on our hands, and they particularly like to hide in skin creases and under your nails. There are many thousands and thousands of germs on your hands right now.


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There are good and bad germs. Good germs live on your skin to keep it healthy. Bad germs – what scientists call “pathogens” – can make us sick.

We don’t know if bad germs are on our hands because you can’t see them. The best and easiest way to remove bad germs is washing them away with soap.

It’s a good idea to wash your hands after you go to the toilet, after you blow your nose, before you help prepare food and before you eat. Otherwise, when you touch your mouth, nose or eyes you might accidentally get a bad germ from your hands into your body – where it can make you very sick.

If you’re not a nurse or a doctor you don’t need to “kill” all the germs on your hands. You just need to wash the germs away. Soap is amazingly good at doing this.

Make sure you wash every nook and cranny of your hands. Flickr/World Bank, CC BY


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Soap gets foamy when we rub it with water between our hands. Foam makes it easy to move soap all around your hands and fingers. While we move soap around, it lifts up invisible oil that holds germs onto your hand. Under the running water we can easily wash off the soap, and all the invisible oil and germs along with it.

If you just use water without soap, the germs will stay on your hands. That’s because water alone can’t lift off the invisible oil where the germs are hiding, often tucked away in tiny creases in the skin on your hands.

We need to rub our hands together with soap and water long enough for the soap to do its job. We need to allow enough time for the soap to make foam, lift the oil holding onto the germs, and rinse them all away.

How long is long enough? Try singing the Happy Birthday song as you rub the soap and water between your hands. Flickr/Lucille Pine, CC BY

How long is long enough? Try singing the Happy Birthday song as you rub the soap and water between your hands, especially rubbing the soap and water over your fingers and fingernails where germs love to live. If you get through the whole song, you are giving the soap long enough to do its important job.

Don’t forget to rub your hands on a clean towel to remove any bad germs that could have been left on your hands.

When we wash our hands with soap and water, the soap lifts up both the bad and good germs and the water washes them away.

But don’t worry – all the good germs that keep your skin healthy will grow back very fast.


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Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

ref. Curious Kids: why do we need soap? – http://theconversation.com/curious-kids-why-do-we-need-soap-109083