eli5 Why does the handwash/soap only kill the microorganisms but not our own skin cells?


I read how soap kills the microorganisms like bacteria by tearing apart their cell membranes.

Does that affect our skin cells also, does the top most layer of our skin also dies and we are just too big on cellular scale that we don’t feel anything?

P.S. i know millions of cells die in our body everyday so it doesn’t matter still just curious does soap also kill outer most skin cells?

In: 64

You have a layer of dead, keratinized cells overlaying the living skin cells. This offers some protection from chemicals. Notice that when you have a cut and this barrier is no longer intact, soap stings.

The top most layer of your skin is already dead. As our skin cells move from the inside to outmost layer the cells get smaller and filled with keratin until your left with a layer of lots of hard dead cells.

Soap is an emulsifier, meaning it makes fats and water mix. Both our cells and bacteria have cell membranes made of fats so the soap makes this mix with water and cause them to burst. It also carries them in tiny bubbles that can be washed off out skin.

This process does affect the top layer of skin cells but as said they are already dead and the skin is constantly replacing itself, so it has no overall effect on us.

I think others already answered your question, I just want to note that there are many bacteria that can easily survive being exposed to soap. Mainly Gram-negative bacteria. These have 2 membranes.

It’s mostly the act of rubbing and rinsing that makes them go away, not the soap itself.

Others have given good answers but I wanted to mention “soap” is technically the “salt of alkali metal”. There are many, many soaps that behave in different ways. Soap molecules generally have a side that binds to water and a side that binds to fat but they bind at different strengths depending on the soap type.

Some soaps can bind so tightly to outer lipid layers of bacteria that they cause them to burst. Others don’t bind so well but they do create water spheres which basically surrounds dirt and bacteria.

So why don’t soaps hurt our cells? Because the soaps that people choose as handsoaps are generally mild to cells but still good at making water spheres. Basically they work by just making it easier to wash away bacteria by surrounding them with water rather than killing them.

However, if you wash your hands with some industrial soaps you may notice that your skin might get irritated… This is because those soaps may be affecting the cell walls of your skin and damaging them.

So the answer is: there are many types of soaps. We choose soaps that make it easier to wash away bacteria and generally we don’t choose soaps that lyse cells as they may cause irritation. Turns out just washing away bacteria works as well as killing it in terms of preventing disease.

Edit: I should add that there is a broader class of chemicals called “detergents”. They don’t necessarily have to be salt of alkali metal, so not all detergents are soaps, but all soaps are detergents. Detergent is just a chemical that is a surfacant used for cleaning. A surfacant just breaks the surface tension between between water and a solid (or other liquid and solid or liquid and liquid), making the solid easier to wash away. Obviously detergents are great for removing dirt and washing away bacteria. It is soap’s detergent behavior that we most value for washing away bacteria and dirt.

Most soaps do not kill organisims on its own unless it has an active ingredient for this specific function, but removes them from the skin emulsifying all the fatty acids on the skin and removing them which can also include cells that are not firmly attached to the skin.
This is why it is recommended to fully cover one’s hands with soap and rub for at least 20 seconds for the emulsion to occur and then rinse. When a proper hand wash is done one can feel the skin dry as the soap removed most of the fats and oils from the skin. In a way you are not killing cells but removing them from the skin.