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
Hands touch many things, including bathrooms and door handles touched by many people. The germs on your dishes are not likely to be as bad. Hands also have a complex shape that makes them harder to wash. And best practice for dishes is a long time in a hot dishwasher with detergent.
I don’t think washing your hands or dishes is meant to kill germs or bacteria. Rather, it’s to wash particles off. Hands are shaped weirdly, have nooks and crannies. Dishes are easier to wash.
they came up with 20 seconds so that everyone who actually tries will reach every part of their hands.
there are a lot if videos on youtube where people “wash” their gloved hands with ink, so you can see which parts they have already reached.
it just takes a while to get between the fingers, on the backside, the outer sides, fingertips and nails,…
well, if the dishes weren’t left overnight, there aren’t that much bacteria on them, mostly food remnants (which are a perfect place for bacteria to live, though). dishes on their own, though, aren’t a good place for bacteria to live on.
The 20 seconds hand washing is to encourage you to wash all areas of your hand, you can do it quicker or slower but as long as you wash all over, it achieves the same results. Similar to the dishes, you wipe all areas until it’s clean. Hands are a more complex shape than a dish hence why it takes longer.
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.
The main property of soap is that it is a surfactant, not an antibacterial agent. It basically makes it so that things don’t stick together. Washing hands for 20 seconds basically gives the chance for you to get soap on every part of your hands so that it can break the surface tension of everything on your hands, allowing the water to rinse oil and bacteria that would otherwise either separate from the water or cling to the hands.
Dishwashers run for 20-60 minutes at temperatures above 120 degrees F. The soap serves the same purpose. The main difference is your hand’s don’t have charred food residue burnt onto them while baking at 350 degrees.
Plates are smooth, flat and typically stored bone-dry. That’s a very inhospitable environment for germs. Anything not removed in the cleaning will just die in place later. Your hands, however, are a germ wonderland. Nooks, crannys, folds, oil, moisture. Gotta scrub em out.
The 20 seconds is to give the soap time to disrupt the lipid bilayer of the virus – effectively killing it and rinsing it down the drain, so its important to soap for long enough [one article on this ](https://www.sciencefocus.com/news/coronavirus-can-hand-washing-really-stop-the-spread-of-covid-19/)
Simply put, bacteria won’t stick to a non-porous surface and by using a detergent or soap you essentially smother your hands in a product of the soap called a surfactant that reduces the surface tension (that slick feeling) and creates a film-like barrier between your skin and the bacteria which allows the bacteria and germs to slide off your hands when you rinse the soap off.
Your hands are extremely porous and come into constant contact with exposed liquid transition points where the bacteria can transfer and thrive within your body such as rubbing your eyes, scratching inside your ears, biting your nails, picking your nose, cuts on your hands and fingers, etc.
The vast majority of dishware is non-porous and doesn’t have recesses or compostable organic material for the bacteria to stick to and grow. This is why food left on a plate will eventually mold, but they are islands of mold only bc they have a source of organic material to feed off of. Additionally, machine dishwashers also employ hot water, heat, and steam to sterilize the dishware, which would scold your skin and cause blistering. Harsher solvents are also used, such as jet dry using chemical agents to reduce hard-water spots and facilitates quicker evaporation. Or Finish detergent powder which is strong enough to cause considerable joint pain and swelling if exposed to repeatedly for lengthy periods of time, but it is better at dissolving organic material without the need for direct scrubbing pressure and is highly soluble in water.
However, if you mean more hand-washing dishes, much of the same applies. You use a softer solvent, such as Dawn, so the skin on your hands doesn’t dry out and crack, and the water is a bit cooler so you’re not boiling yourself alive, but you work harder to remove the stuck on debris.
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