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M8asonmiller t1_it9vzjq wrote

Reply to comment by sterlingphoenix in ELI5 - Why can't you just wash away germs on teeth with soap? by wolf_metallo

It does kill germs, but it's not abrasive enough to lift off plaque. A long time ago toothpaste used to be made out of ground-up bricks for tooth-scraping power.

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greatvaluemeeseeks t1_it9yr77 wrote

Soap by itself doesn't kill all germs. Cell membranes are made from a phospholipid bilayer. They are made from a molecule with one end attracted to water and one end attracted to oil. The molecules are arranged so the ends attracted to water are pointed towards each other. Soap with a little bit of agitation will rip these membranes apart, but some bacteria and viruses have a hard protein layer that protects them.

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