Eli5: How do soap and water actually kill microbes?


I broadly understand how alcohol-based sanitizers work, but how do simple soap and water do so? Also, how important is the temperature of the water?

In: 5

For the most part, they don’t. They make things slippery so that all of the microbes and stuff that can harbor microbes can be washed away. Warmer water tends to be more effective.

Soap works in two ways, first it binds to oils in your skin and in dirt and to the water as well, letting you wash it all off as a single complex. Soap’s ability to bind to fats also means that it disrupts the lipophilic (attracted to fats) portion of cell membranes. The result is that soap can literally dissolve the bodies of many microbes.

Soap and water work by loosening and removing dirt, oil, and microbes through physical and chemical processes. Soap breaks down the protective lipid membranes of microbes, deactivating them. Mechanical scrubbing and rinsing then help wash everything away.

Soap is a surfactant. It disrupts the cell walls of the bacterial pathogens, and the viral envelopes.

Particles can be broadly categorized into water loving or water fearing. Salt is so water loving, it’ll just dissolve into it. Oil is so water fearing that you can shake water and oil up as much as you want, and they still separate into layers.

Water loving particles are easy to wash off. Just rinse with water and they’ll follow the water down the drain. But the problem is the water fearing particles that would rather stay on your skin than follow the water.

In comes soap. It’s super power is that one half of the particle is water loving, while the other half is water fearing. So when soap is dumped into water, it starts forming little bubbles. The water fearing half of the particles hides from water on the inside of the bubble. And the water loving half is happily on the outside of the bubble next to all the water.

So if you’re a bacteria with a membrane made of water fearing particles, where’s the best place to get away from the water? By also hiding inside those soap bubbles. But since the outside of the bubbles are water loving, the whole thing still gets washed away by water.

(Also, the water fearing half of the soap particle can sometimes wedge itself into those water fearing membranes and rip the bacteria apart, actually killing them).