system
Given the following post, respond as if you're commenting on Reddit:
human
How long does it take soap to “remove” bacteria?

I’ve seen that the recommended amount of time for washing hands with soap is 20-30 seconds. I know that friction from rubbing is what allows the soap to  remove the bacteria from your hands, but is the 20 second rule constant? Is that just to ensure you cover the full surface area of your hands?

If I get my wrist dirty, do I need to rub it with soap for 20 seconds? What about on other materials like ceramic or steel? Does the type of soap impact the amount of time you should spend creating friction (i.e dish soap vs hand soap)?
gpt
Soaps/detergents are useful because they make waters surface tension weaker. So when you are washing your hands that are dirty, that "cutting action" of soaps happens because they separate oils and substances from your skin. Same for dishes and also clothes. 

I think the 20-30 second rule is mainly used to enforce hygiene in a work place by law, "all employees must wash their hands before returning to work". This general practice is probably used as the standard for washing our hands.