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Soap contains emulsifiers which break down the membrane of bacterial cells. Emulsifiers are chemicals which allow oils (hydrophobic) and water (hydrophilic) to dissolve or mix in one another. They’re in everyday items such as ice cream paints etc.

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The sponge is definitely carrying bacteria from dish one to dish two. But the soap + scrubbing is making the mechanical removal of food and bacteria much easier. Basically freeing it from adhesion to the surface of the dishes so that the final rinsing with water carries the bulk of it away and down the drain. I personally think sponges are gross and not good for cleaning things involved with eating. They harbor bacteria like it’s nobody’s business and you’re right to be questioning this. I’d recommend switching to a plastic bristled brush that you can fully rinse with before each dish or item that you wash.

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Thanks for the answer, I’ll definitely be looking in to finding an alternative.

Very interesting, thank you!

What is ice cream paint?

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Really good idea to keep your sponge/scourer dry between washing sessions, don't leave it in the sink to stay moist and help bacteria survive. I often nuke the sponge/scourer in the microwave. Add soap, some water, put in bowl or plate and nuke on high for 2 minutes. Also has the benefit of steaming up the inside of the microwave and makes the microwave easier to clean.

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I rarely use a sponge but when I do I microwave a wet sponge for two minutes to kill bacteria. It’s extremely hot afterwards so be careful.

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Does soap also break down the cell membrane of animal cells?

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A bacteria cell consists of many different parts, but the relevant one here is called the "Bi-Lipid Layer", which is a layer of lipids that enclose the cell and essentially function as its skin.

Lipids are a group of compounds that include organic fats, oils, and waxes.

In general, most things are either hydrophobic (fat/oil soluble, but not water soluble) or hydrophillic (water soluble but not lipid soluble). Things are usually one or the other.

Detergents are somewhat unique in the fact that they are both hydrophillic and hydrophobic - they bind to both oil and water, and allow them to be bonded together in very close proximity, where they would usually very strongly repel each other.

So, you have a bacteria with its lipidous cell wall, immersed in water. The water is normally repelled by this layer, preventing the bacteria from dissolving into it. Enter a molecule of detergent. This molecule bonds strongly to the bacteria's protective lipid layer. This causes a very strong attraction to the surrounding water, while adjacent lipid molecules, which are not bonded to detergent, strongly repel the water. This bonding and attraction between a water molecule and the lipid molecule is now so strong that the bacterial cell wall rips and ruptures apart, thereby spilling its innards and killing the cell.

Edit: a commenter corrected my phrasing - the terminology is lipid bilayer, not bi-lipid layer.

Yes.

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That's when you take too big of a bite off your cone and a little ice cream gets on your nose 😀

Your outermost layer of skin cells is relatively safe from this because it's made to be less reactive and protect from outside threats like this (My detailed anatomy knowledge is fuzzy, but my understanding is that you're basically protected by a layer of keratin, which soap does not act on), but yes it does break down animal cells, and this is one of the main reasons that soap is toxic to ingest.

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Do you mind if I ask where you’re from? This is the first time I’ve heard bi-lipid layer instead of lipid bilayer.

Australia. And I've just googled it, and I can't find it referred to as bilipid layer anywhere, so my best explanation is a little brain-fart that somehow mixed up the phrasing in my head and got stuck that way lol.

Thanks for catching it!

I would’ve thought that if bi-lipid layer was normal anywhere, it would be Australia. Everything is reversed there since you’re all upside down, no?

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>bi-lipid layer

You might have googled the wrong place, google scholar has it: https://scholar.google.ca/scholar?hl=en&as_sdt=0%2C5&q=bi-lipid+layer&btnG=

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So I can wash my hands in ice cream? Does ice cream kill covid?

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Well there ya go! Thanks

Can't the Bacteria evolve to prevent this?

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Honestly, I don't know - evolution is capable of producing some pretty incredible results - but I doubt it. It would require cells to either use something other than lipids to form their outer membrane, or to reinforce the layer to the point that the attractive molecular forces cannot break it. Such an adaptation would so fundamentally change the way cells currently operate, that any drift in that direction would probably be incompatible with life.

A suitable analogy might be to ask if vertebrates could evolve to be totally immune to fire. Like yeah, maybe, but the required physiological changes would be totally incompatible with life as we know it.

Detergents are very similar to soaps which work in the same way. This is why soap and water is an excellent way to kill bacteria and germs compared to alcohol based rubs. Alcohol will kill the germs, but they’ll remain there in almost a nutrient soup for other germs. Washing with soap and water kills it and disposes of the traces.

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Even if they don’t rupture, they’re getting washed away by magnitudes more water than they can deal with. (In a similar vein, I find general spray cleaners just as effective on unwanted insects as insecticides, but with no awful odors/volatiles, and ready to wipe clean.)

Bacteria can produce biofilms in an attempt to hold position, hence the need for scrubbing to break up their defenses.

Some soaps used to have antibacterials, but that just resulted in resistant bacteria wherever they ended up.

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Not easily like with Antibiotics. Antibiotics are like scalpels, they target 1 very specific part of the bacteria and disrupt that part. By changing that part slightly, the antibiotic stops having an effect (or alternatively, they set up systems to pump the molecules of antibiotics out of the bacteria before they can do harm).

Meanwhile, soap is almost like a fire. It simply rips the entire membrane apart. In order to prevent this, they'd need to fundamentally change how the membrane is constructed. Fundamental changes like that are, while not impossible, basically unheard off in evolution.

Yes. That's why getting soap in an open wound is painful, and why drinking soap is so dangerous.

However, your outer skin is mostly immune to this as it's not made of living cells, but rather a layer of dead cells that made some structures that resist this before they died.

Its hard to imagine in between steps of evolution towards "detergent resistance/immunity" that would be selectively advantageous. Is that kinda what you're getting at?

But it’s still wise to change out/boil the sponge periodically? How come some sponges start to smell sour given this phenomena?

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then why wasn't it enough to wash wounds with soap to prevent infection before antibiotics? And how come it doesn't dissolve the lipid bilayer around human cells? And what about all the bacteria that live on soap?

in addition to that. soapwater encapsules dirt with soapwater so dirt can no longer stick to your skin or sponges and can be washed away. with washing it dirt away you wash away lots of bacteria and one of the main problems with bacteria is: the more are there the more likely it is to be infected. so soap does not only destroy bacteria, it also washes them away.

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pretty sure this is false in most cases. What really happens is the bacteria cant cling on to anything and they get washed away. Dish soaps have antibiotics though which will kill bacteria.

A good example is toothpaste. All the bacteria in your mouth don't just die. In fact that would be bad, because something worse would take over.

there may not even be too much of an in-between step to begin with. whether it is baby steps or a leap, it is both difficult to imagine

So soap in the mouth for cursing damages more than just your emotional stability?

The habitat that requires this kind of resistance is the sewage system, I wonder how many generations of human are required to contribute to their evolution

I use a plastic bristled brush too. Anytime I run the dishshwasher I'll put it in there to kill off additional bacteria. Otherwise it gets a thorough rinse and set upright in the counter drying rack. I don't think I will ever return to sponges.

From my understanding many soaps contain sulfactants and surfactants that disrupt the sulfur and surface tensions in the outer membrane of bacteria cells.

This disruption, in addition to lipid interactions and mechanical abrasion, makes many bacteria weaker; when the bacteria is then transferred plate to plate and to sponge it is less able to survive or reproduce.

Also after bacteria interact with soaps, regular water can act as a mild solvent further degrading the bacteria (and washing it away).

I'll address your questions one at a time.

First, detergents are close to 100% effective at killing germs, but they can only be applied to exposed surfaces - any bacteria that have infected deeper tissue, or are hidden in nooks and crannies, cannot be reached by detergenty water, so other treatment is needed. Detergents cannot be applied internally - see the next part of my response for why. With that said, regular hand-washing is one of the most effective disease-control measures we have.

Second, detergent absolutely does have this effect on human tissue. Your skin cells in particular have evolved to be quite resilient, but detergent can and does kill them - fortunately your skin is made of many layers of cells, so damage is not immediately evident. Your skin also secretes oils to keep it soft and protected, and these oils use up a good amount of detergent before it can get to the cells themselves.
But wash your hands with strong dish soap many times a day, and after a few days you'll develop irritated, dry, cracking skin, with bleeding sores. This is also why the whole tide-pod thing was so dangerous - your internal tissue has not developed the same resilience as your skin has, and eating high-strength detergents can cause serious damage to your digestive tract.

Third, how can bacteria live on soap? Partly because of the reasons I mentioned in the previous paragraph, most body soaps have been developed to not so much kill bacteria and other cells, as dislodge them and allow them to be washed away. This causes minimal damage to your skin, but still cleans it - the bacteria have been washed off, rather than killed. Furthermore, those soaps and detergents that ARE lethal to cells (like dish soap) are only effective in the presence of water. See my original comment for more info there.

That's true. Most hand-and-body soaps are developed without detergents, and wash away bacteria cells rather than kill them - this is because detergents have the same effect on your skin cells as they do on bacteria, and repeated use for cleaning your body would cause injury over time.

Sponges, especially large and thick ones, are extremely porous and have an incredibly high surface area. The more surface area there is, the more space bacteria has to grow - especially because a sponge likely has bits of food debris lodged in it to feed them. This also makes it difficult for detergent to fully penetrate every nook and cranny, and a high bacterial load, combined with the large amount of lipids typically present in food, will very rapidly "use up" all available detergent in the sink.

I wouldn't resort to cooking my sponges though - I don't like the idea of broken-down plastics and petrochemicals from synthetic sponges making it onto my plate. Letting a sponge completely dry out between uses is pretty effective at killing germs, and always make sure you use lots of detergent when washing your dishes. And yeah, regularly switch to a new sponge.

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Thanks for the answer. Personally I only use Brillo sponges for heavy stuff and toss. I prefer dish cloths because I can wash them.

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Not to take up anything from the answer as it’s amazing, but its two layers of lipids, so the bilayer is def more correct.

What would the difference specifically be?

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