When you do the dishes and have a little residue of cheese attached to your fork that contrains you to pass a second time your sponge/dishwashing liquid to be perfectly clean.
If we applied this logic to microscopic things on our hands, that would mean that it’s better to clean them twice “just to be sure”. Since it’s impossible to know if we have particularly resistants microbes or something like that, one more soap/rince seems worth
Is this manner of thinking sounds accurate in a scientific way ?
In: Chemistry
I’m not sure if this is ELI5, but yes, the more you wash your hands, the more bacteria you’d scrub away.
So yes – I’d say that if you wash your hands twice, you’ll probably get rid of bacteria that you missed on the first attempt.
The best way to wash your hands is to get soap, and sing ‘Happy Birthday’ to yourself while working your palms, fingers, back of hand and in between fingers slowly and thoroughly.
Say we have a big plate, and it has a million dots on it. Each time we wash it, we remove 99% of what’s on the plate. After the first wash, we’ll have 10,000 dots left on it. After the second wash, we’ll remove 99% of that 10,000, leaving 100 dots. It’s unlikely you’ll ever get it perfectly clean, but it depends what you’re comfortable with. You could stop at two, but why not do three? Why not one hundred times? That can become a compulsion, which is bad for you. Ultimately, very very few things will ever be perfectly clean, but all we can do is work to an acceptable standard.
In hospitals, we have a set hand-washing routine in which you do lots of little steps repeatedly – palms together for 5 seconds, then around your thumbs for 5 seconds etc.. That’s to ensure we hit each part of our hand, and scrub it enough to clean as much as is practical.
It’s not worth the skin damage that over washing can cause. It will remove more bacteria but as long as you’re washing thoroughly the first time then it’s fine.
I tend to think it’s more important to wash your hands correctly the first time, than wash them twice. I’ve always tried to stick to this rule, and I’ve been OK. That being said, I hate it when I go to a restaurant or a stadium and they only have cold water to wash your hands, I always like to use hot water. So if it’s only cold water, sometimes I will wash twice if I feel the need.
If you just never wash your hands, your immune system will be stronger from constant bacterial exposure and you’ll never get sick, while also killing off people with inferior immune systems.
> Is this manner of thinking sounds accurate in a scientific way ?
it *can* be, but it depends on the particulars.
in the case of the dishes, the amount of material you can remove in a single scrubbing action is limited, so you have to break away the material layer by layer. in principle, you could have just scrubbed more the first time and gotten all of the material off.
for most instances of hand-washing, this sort of mechanical limitation isn’t a concern. the soap and water solution on your hands can mechanically reach all parts of your hand, and it will remove or destroy 99.9% of contaminants.
> if I wash hands twice, are they significantly cleaner ?
if you wash your hands twice, you’ll have removed 99.9999% of contaminants in total. technically you did *something* but is that “significant”? no.
this relationship of probabilities, percentages, and number of trials is part of statistics and *does* significantly impact many things. medicine in particular. when you get tested for something, like covid or strep, it’s very normal for them to run multiple trials to decrease the likelihood of faulty results.
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