Why Soap Washes Away Dirt
We wash our hands many times a day. We do it after we play outside, before we eat, and after we touch dirty things. Usually, we use water and soap. But have you ever asked yourself: why do we need soap? Why is water not enough to clean our hands? The answer is in the science of soap.
The Problem with Water and Oil
To understand soap, we must first understand dirt. Most dirt on our skin is mixed with natural oils and grease.
Water is great for cleaning many things. However, water and oil do not like each other. If you put water and oil in a glass, they do not mix. The oil always floats on top of the water.
Because of this, when you have oily dirt on your hands, water alone cannot wash it away. The water just slides over the oil. It cannot grab the dirt.
The Secret of Soap
This is where soap helps us. Soap is special because of its molecules. A molecule is a very tiny group of atoms.
Each soap molecule has two different ends:
- The Head: This end loves water. It wants to hold onto water.
- The Tail: This end hates water but loves oil and grease. It wants to hold onto oil.
Because of these two different ends, soap acts like a bridge between water and oil.
How Soap Cleans Your Hands
When you rub soap and water on your wet hands, an amazing thing happens:
First, the "tails" of the soap molecules run away from the water. They find the oily dirt on your skin and stick to it.
Second, the "heads" of the soap molecules stay in the water.
Next, as you rub your hands together, the soap molecules surround the oil. They form tiny round drops with the oil trapped inside.
Finally, when you rinse your hands under the tap, the running water grabs the "heads" of the soap molecules. Because the "tails" are holding the dirt, the water pulls the soap and the dirt away from your skin together. The dirt goes down the drain!
Wash for Twenty Seconds
Now you know how soap works. But it needs time to find all the dirt. This is why doctors say you should wash your hands with soap for at least twenty seconds. That is about the time it takes to sing the "Happy Birthday" song twice.
Question for you: How many times a day do you wash your hands?