Does Soap Really Kill 99.9% of Germs?

soap bubble in airFrom kissing to touching our phones, there are many everyday practices that result in the exchange of germs. The go-to answer is of course to wash our hands with soap and water, but how well does soap really work? To figure this out, we need to learn how soap works.

First, let’s define a germ. A germ is a microscopic particle or organism that can make us sick. This includes bacteria and viruses. Because of the oils on our skin, most of the substances that we want to wash off of our hands, be they germs or dirt, adhere to our skin. The associated germs can be removed using a solvent such as alcohol or kerosene.

Soaps used in hospitals are often strong and alcohol-based. However, alcohol and kerosene are, to varying degrees, toxic on their own. This makes them not ideal for frequent in-home use. Not to mention smelling like kerosene all day would be displeasing. Soap is a solution that allows us not to use these substances.

Soap works in a more mechanical way, rather than dissolving oil. It essentially works to convince the oil particles and their associated germs to link up with water molecules. This allows the germs to be more readily washed away.

In order to picture this, we need to think about what a soap molecule looks like. A soap molecule is structured like a long chain of carbon and hydrogen molecules. One end of the chain is called the hydrophilic end, and it readily joins up with water. The other side is called the hydrophobic end, and it avoids water. Instead of attaching to water, the hydrophobic end readily attaches to grease. When you wash your hands, the hydrophobic end attaches to germ-hosting oil particles while the hydrophilic end coaxes these particles toward the water to be washed away. The hydrophobic end also goes between water molecules in order to remove itself from water. This forces the molecules apart and thus leads to reduced surface tensions.

If you want to see an example of how soap reduces surface tension, fill a glass of water almost to point of spilling. Surface tension is what makes the water stay in the glass. If you tap the top with a soapy finger or put a drop of soap in the glass, the water will overflow due to a decrease in surface tension.

Now that we know how soap works, let’s get to the bottom of this. Does soap actually kill 99.9% of germs as people claim it does? Many companies make this claim, but it is far from true. The statistic of 99.9% germ removal is based on laboratory results. These tests are conducted in conditions very different from the messy conditions of our everyday lives. Additionally, the claim of 99.9% could only refer to more common germs, and the tests involve a thorough scrubbing. Additionally, soap doesn’t kill germs; it just removes them.

Even in the best case scenario in which you remove 99.9% of germs every time you wash, 0.1% of germs can still be a lot of germs depending on how many germs were already on your hands or on the surface you cleaned.

Using soap and water is certainly better than not washing your hands, but soap isn’t nearly as effective at removing germs as people state. This is especially important in healthcare facilities, where germs can be transferred to patients and throughout the facilities even after washing hands. Hand-washing is a crucial practice. Hopefully, we can find a more effective alternative to soap in the future.

Click here to the listen to the full “Everyday Einstein: Quick and Dirty Tips” podcast.

from Efrain Gonzalez MD


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