What 0.1% is left when you kill 99.9% of germs with soap?

By Kevin Kusnadi, 2019 Alumni.

When we use a soap that says “kills 99.9% of germs” on its label to wash our hands, what happens to the 0.1% of germs in our hands? Does it get intentionally saved so it can live to tell the tale of how a mighty soap wipes out an entire population? What is really happening to that ultra-powerful one-in-1,000 germ?

Image by AJ Cann on Flickr

The battle between soap and germs

A germ is a microscopic organism that could potentially make us sick, be it bacteria or viruses. Germs can come in contact from daily objects such as our phones, banknotes, door handles, shaking hands with another person, and the list goes on.

How do they end up in our hands? There are sweat glands underneath our palms that produce sweat and oils that become an ideal medium for the germs to adhere nicely on our skin. Germs stick to our hands because of the oils on our skin.

So the main objective of soaps is to destroy the “home” of germs by removing the oil from our hand that will subsequently kill the germs. Alcohol and kerosene are solvents that can effectively destroy the oil, but they are quite toxic for frequent home use. Imagine if you smell like kerosene all day? This is why soaps in the hospitals and laboratories smell a bit funny because they contain alcohol and are generally stronger than soaps found in the grocery store.

A more ideal solution is to use soap, but this brings another problem. Since commercial soap normally does not contain alcohol unlike soaps in the hospitals, rather than destroying oil particles (and their associated germs), soap molecules work by dissolving the oil with water which is then washed away. Therefore, its efficacy in killing germs is always been debatable.

Image by Irina Ba on Unsplash

Does soap really clean our hands from germs?

Most soap manufacturers advertise their product capable of killing 99.9% of germs, but does it truly happen? One thing we know is that claiming just short of 100% avoids them from being sued, but their claim does come from lab results.

So the next logical question would be, how reliable are their lab results? Generally, their lab tests and results are trustworthy, but there is a big pitfall that not many people know. Their test procedures typically consist of placing germs on a surface, wiping that surface with the soap, and then finally the remainder of the germs are analyzed.

The pitfall arises because their test conditions are different from our messy everyday life. Obviously, the inside of a laboratory is much cleaner than the outside world, so the results may not be true in every condition.

One study demonstrated that handwashing with soap and water removes the presence of bacteria to only 8%. This indicates that washing hands with soap still does not leave germs to 0.1% even when done in a laboratory, let alone a real-world application.

One important thing to note is that soap is not really killing the germs in our hands, but rather washing them away. In a scenario where a soap really removes 99.9% of germs, the remaining 0.1% may sound insignificant. But when we are talking about the number of germs, we should be considering millions of them which is why it could still be dangerous. However, as long as we maintain regular sanitation habits supported by a strong immune system, we should be fine!

So when a soap manufacturer claims that their products kill 99.9% of germs, they are technically correct but practically wrong. Although their lab results are not entirely misleading, it is indeed a powerful marketing message!