Eli5: Why are we told to wash our hands for 20 seconds to kill all the bacteria etc, but not told anything similar for dishwashing? What makes dishwashing different, if anything?
In: Biology
Because dishwashing has several methods to disinfect, whereas hand washing has just one.
Dishes can be sanitized through agitation, chemicals, or high temperature. Agitation is the manual scrubbing with a rag or scrubber to produce friction (assisted by detergents). Chemical methods include diluted chlorine solutions or quaternary sanitizers submerged for 1 minute. High temp would be exposure to hot water jets in excess of 150 degrees Fahrenheit for 30 seconds or more and hot rinses or steams sometimes as hot as 180F. Many dishwashers, whether people or machines, use a combination of these three methods.
Hand washing, however, can only be subjected to one of those methods: agitation (friction).
It is possible to disinfect hands with diluted chlorine (or quat sanitizers) but it is not efficient to fill a basin and submerge hands for 1 minute every time a hand wash is desired. Nor is it safe to wash hands under water in excess of 150F, as it will scald. There are hand sanitizers, but that’s different from washing. You could also wipe a rag with sanitizer on a plate. But again, not the same as washing.
That is why a running a tap with soap, water and using friction is the standard method for hand washing, while dish washing can use a combination of methods mentioned above.
As for the 20 seconds rule. It is basically just the agreed upon time by various health organizations to ensure people are applying friction long enough. Sometimes they say sing happy birthday two times in a row instead.
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