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
Part of it involved how porous a surface is. Dish ware usually isn’t very. Dish soap has two factors that make it helpful for cleaning. One of those is the fact it’s a surfactant, it slips into pores and creates a slippery environment. The other is the fact that it’s amphipathic because it’s polar and non-polar, this means it had properties that are hydrophobic (water hating) and hydrophilic (water loving). This property allows soap to act as a bonding bridge between water and lipids/oils. (It gives the “grease fighting” characteristic) This makes it effective against phospholipids. The other aspect has to do with moisture content. Usually, dish ware in a dishwasher goes through detergent washes and rinses that reach high temperatures. Some dishwashers also incorporate steam or heating elements to dry and sanitize the dishes. Hand washed dishes typically are given time to air dry before being stored. This dry environment makes it increasingly difficult for bacteria and viruses to thrive over longer periods of time.
Your hands on the other hand are extremely porous, so the act of rubbing your hands help drive the surfactant into the pores. You must also cover your hands with suds. Proper hand washing technique is as important as time taken. You can run your hands under a faucet but if you don’t properly scrub your hands, viruses and bacteria may persist. Surgeons use specialized soap, hand scrubs, temperature controlled water, and longer scrub times, as well as more stringent scrub measures to ensure their hands are as free of contaminants as possible, and then they’re followed by a glove.
If you throw dishes in a dish washer machine it sterilizes the dishes with extra hot water. Restaurants often use a bleach water mix to rinse and sterilize. Otherwise you are not killing any bacteria, just hoping you wash it away.
dishes are generally for personal use by you and those you may be cohabitating with, and unlike your hands, you will not be opening public doors or touching public fixtures, people and objects with your dishes
Public Health Sanitarian here; excellent question! In fact our hands and nails have lots of places for germs to ‘hide out.’ Twenty seconds of scrubbing has been shown to reduce bacterial ‘load’ about 99%.
As stated above, utensils and dishware are constructed of materials and design with washability in mind. Interestingly, most modern food codes require restaurant dishes to be sanitized *after* washing and rinsing. This usually involves a solution of bleach water or quaternary ammonium to reduce bacteria by 99.9%.
Technically, the soap doesn’t necessarily kill the bad stuff, but it binds to it, then binds with water to quickly wisk it safely down the drain and remove it from your hands, so you cannot place it in your eyes, mouth or nose where it can take hold and grow, making you sick.
[https://www.defeatdd.org/blog/how-does-soap-actually-work#:~:text=When%20you%20wash%20your%20hands,stubbornly%20clinging%20to%20your%20skin.](https://www.defeatdd.org/blog/how-does-soap-actually-work#:~:text=When%20you%20wash%20your%20hands,stubbornly%20clinging%20to%20your%20skin.)
You don’t less than 20 seconds cleaning a dish? Remind me to never use your dishes.
Its part because bacteria wont stick to glass, porcelin, silverwear ect quite as hard as it will stick to skin and part because the people making these reccomendations know humans are gonna screw it up.
If you ever see a kid washing their hands theyre absolutely trash at it. They dont fully soap up they just kinda rinse their hands without scrubbing everywhere properly but if they were to wash a full 20 secounds then no matter how trash they are as scrubbing theyll at least get it fairly clean. These reccomendations are set to avoid human error because people are bound to get lazy or do things wrong and half-assed washing your hands for 20 secounds is better than half-assed washing for 10.
All of this other scientific stuff, but also I rarely take my favorite plate to the mall and touch stuff with it.
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.
If you work in the industry in the USA, there is a 3 sink+Sanitizer process for most commercial dish washing, involving cold water, hot water, and bleach sinks…then an ultra hot sanitizer machine.
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