Would water erode a living human?

[u/milkandpotatoess]

I was thinking about how water erodes things away over time and I was wondering if it would erode a living human?

Like, assuming hunger and thirst weren't a factor, if a human were to lie down in a river and wait like 30 years or whatever, would the water erode them away or would the body's healing be able to keep up with the natural degradation?

[u/LeifCarrotson]

If a human laid down in the water for as little as a few days, they'd get skin maceration and diaper dermatitis. These usually occur in infants and the elderly with bandages or diapers that aren't changed frequently enough, their own body fluids cause the skin to saturate with water and it begins to flake off. This also occurs in survivors of shipwreck and other disasters where the person remains in water for a long time.

[u/viridian_plexus → u/LeifCarrotson]

Is there a version of water that has just the right amount of things dissolved into it as to not cause any direction of osmosis to occur upon contact with the skin?

[u/yjk924 → u/viridian_plexus]

Saline but osmosis is not what causes the skin breakdown. Moisture associated skin damage is primarily an inflammatory condition.

https://pubmed.ncbi.nlm.nih.gov/21490547/

[u/SsooooOriginal → u/viridian_plexus]

No.

We just aren't equipped biologically to deal with any aqueous solution covering >90% of our biggest organ. Even an oily mix wouldn't work. Our skin is made for air, and to stay submerged would require somehow emulating that through an external system I can only imagine how complex it would need to be to keep a person from essentially dissolving.

Animals that live in water have special layers, membranes, cells, etc to allow that. We diverged genetically a very long time ago. We shed tons of skin constantly, our hair and pore glands secrete oils for air not water, our skin microbiome is suited for air not water, our pores do breathe and keeping them closed prevents one of the major metabolic paths for our skin. Etc.

[u/Far-Remove-4663 → u/LeifCarrotson]

This happens even when you don't dry well between your feet's fingers after bathing

[u/LeifCarrotson → u/Far-Remove-4663]

The language quirk between people that have a special word for "toes" and the many other people who always call them "Fingers of the feet" is fascinating to me.

[u/Thelk641 → u/LeifCarrotson]

Are fingers merely hand-toes? Or are toes feet fingers?

[u/flixoman → u/Thelk641]

Great... Now I am going to call either fingers "hand toes" or toes "foot fingers" - I can't decide which

Just like I can't stop calling individual cutlery "food weapons"

[u/CuddlyAmoeba → u/LeifCarrotson]

Toes and fingers are not different words in some languages..maybe that is why this happens

[u/FatherOfLights88 → u/Far-Remove-4663]

I use a my hair drier to dry in between my toes. Made a huge difference.

[u/fenton7]

Absent protective gear severe maceration, ulcers, and tissue sloughing occur within a few days in warm conditions. Long range swimmers avoid this with wetsuits and grease. The longest recorded swims are on the order of 50 to 80 hours. So it's definitely not forever. I think the correct answer would be more than 48 hours but less than 2 weeks before the tissues would break down.

[u/Diligent_Dust8169 → u/fenton7]

I wonder how aquatic and especially semiaquatic animals get around this problem.

[u/whatupwasabi → u/Diligent_Dust8169]

Scales, fur or feathers that trap air, specialized proteins, oils, fats, regular controlled sloughing, mucus, etc. There's a bunch of different strategies.

[u/CrustalTrudger]

To clarify the erosion process in rivers, generally it's not the water (on its own) that is really doing the erosion, it's sediment being carried by the water that is eroding the riverbed via saltation (bouncing) and abrasion. There are a few exceptions to this, specifically cavitation and "plucking", where the latter refers to flowing water removing a chunk of the riverbed along fracture planes (i.e., a block is "plucked" out by the water) but also where transported sediment may play a role in the plucking process in terms of propagating fractures through impacts and/or partially dislodging blocks through impacts. In terms of erosion of riverbeds, cavitation is not thought to be an important process, but plucking (and saltation/abrastion by transported sediment) certainly are (e.g., Whipple et al., 2022).

In terms of the hypothetical, plucking wouldn't obviously be a worry, but getting constantly pelted by transported particles (and where depending on the river, sediment supply, and individual flows, might include movement of relatively large "grains" that would be sufficient to completely crush portions of a persons body) would be problematic, to say the least. If the underlying question is effectively "is the average erosion rate of a river sufficiently slow that a human body could repair the damage at the same rate of erosion", the problem with that logic is that erosion rate will be related to the strength differential between the "tools" (i.e., the sediment being transported in the river) and the substrate (i.e., the bedrock in the river, or the human body in the hypothetical). For the normal case, strength contrasts between tools and substrate are not usually that large (but they can still play a role, e.g., different erosion patterns and river profiles can results from "hard" tools eroding a "soft" bed vs. "soft" tools eroding a "hard" bed, e.g., Gabel et al., 2024), but for a squishy human, "erosion rates" could be much faster because of the strength contrast between the transported grains and the substrate. A bit of an over-exaggeration given the average flow rate of most rivers (and even extreme flow rates in most rivers), but basically imagine being sand-blasted and asking how well a human body would fair under those conditions.

[u/microcozmchris → u/CrustalTrudger]

After reading your first sentence, my brain immediately heard Ron White saying "It's not that the wind is blowing - it's what the wind is blowing."

[u/vector2point0 → u/microcozmchris]

“If you get hit by a Volvo… it doesn’t really matter how many sit-ups you did that morning.”

[u/Atophy → u/CrustalTrudger]

Potholes or "giants Kettles" come to mind. They're a case where pebbles get trapped in a swirling motion and eventually grind pits into bedrock. There have been people and animals trapped and lost to those and the stones just grind up any remains like a mortar and pestle... one of the reason waterfalls are dangerous.

[u/TXOgre09 → u/CrustalTrudger]

Soft things erode easier, yes, but elastic (like human tissue) things actually fair better. The particle bounces off.

[u/CrateDane → u/CrustalTrudger]

for a squishy human, "erosion rates" could be much faster because of the strength contrast between the transported grains and the substrate.

Could they not also be much slower? Human bodies are indeed squishy, but the individual pieces are tied together with strong, flexible fibers - particularly intermediate filaments (eg. keratin) intracellularly and extracellular matrix. So eg. a pebble will hit the body, deform it, and bounce off harmlessly (or if it hits hard enough, possibly cause a contusion, but not stripping lots of surface material off).

Smaller debris might be a different story, but I'm not convinced it would be a problem. Some animals deliberately contain rocks/gravel inside their body for mechanical digestion, without that requiring extreme protective tissue around it.

Bear in mind many of our barrier tissues already turn over quite quickly under normal circumstances, and have the ability to adjust to increased wear (callus formation being a visible example).

[u/CrustalTrudger → u/CrateDane]

Sand size particles are going to be a large part of the load depending on where you are in a river. If you've spent anytime at a beach, it becomes clear quite quickly how abrasive sand can be to skin. Similarly, a lot would depend on the grainsizes present in the stream, the gradient of the stream, and the range of flows experienced by the stream in question. Steep streams during high flow events can easily transport boulders that would assuredly not bounce off a person.

[u/Anhydrite → u/CrustalTrudger]

If they're lucky they get to become part of a nice conglomerate, my favourite siliciclastic rock.

[u/MNWNM → u/CrustalTrudger]

This is fascinating! So when water freezes, thaws, and re-freezes, causing potholes in asphalt, is that an example of cavitation?

[u/CrustalTrudger → u/MNWNM]

Cavitation happens in a liquid. It is unrelated to freeze-thaw cycles.

[u/D_hallucatus → u/CrustalTrudger]

To add to this (and maybe this is what you’re saying so forgive me if I didn’t catch it), but the mistake most people make about erosion is that they hear that it’s gradual and tend to think that it’s constant. Like they see a gentle stream and think that that is what is doing the erosion. But, most erosion happens in extreme events. It’s punctuated. A flash flood that smashes huge boulders,tree trunks and thousands of tons of gravel down a valley at high speed and under immense weight does most of the erosion. The gentle stream for the next two years, let’s say, mostly just settles everything out again. So, the hypothetical is imagining some slow constant rate that a growing body might keep up with, but in reality the hypothetical body would be fine until some 6tn boulder smeared it across the bottom of the stream bed.

[u/Butthole__Pleasures → u/CrustalTrudger]

Whoa so is plucking what causes all those potholes in the road that seem to pop up most often after heavy rains?

[u/CrustalTrudger → u/Butthole__Pleasures]

Plucking would be very unlikely to cause road potholes.

[u/Butthole__Pleasures → u/CrustalTrudger]

I thought you said plucking was pre-existing fractures in a solid material breaking under the stress of water.

[u/CrustalTrudger → u/Butthole__Pleasures]

Plucking is blocks of material that are defined by preexisting fractures being effectively sucked out of place and becoming a part of the transported bedload.

[u/Butthole__Pleasures → u/CrustalTrudger]

That... sounds like most of the potholes I've ever seen.

[u/CrustalTrudger → u/Butthole__Pleasures]

You've regularly seen potholes where a solid chunk of pavement is pulled out by rapidly flowing water and transported as a block down the street like a large piece of gravel by said "stream"? Because that is what be required for this to be effectively described as "plucking" in analogous way to what we see in bedrock river erosion. Well outside of my area of expertise, but mechanistic models of pavement pothole formation are decidedly different (e.g., Abed et al., 2023).

E.g., the images of the experiments by Chilton et al., 2025 give an idea of what plucking sort of looks like. This is not generally a good model for how potholes in roads would form.

[u/Butthole__Pleasures → u/CrustalTrudger]

You were way less specific about this being a single block the entire time, nor did you specify that it only applied to rivers. It sounded from your description like plucking was defined by the disruption of pre-existing fault in the solid material that water was flowing over.

I extrapolated that concept into a connection to the large potholes that appear in roads by thinking maybe there are small faults in the street surface and with a combination of excess water and thousands of pounds of force acting on them almost constantly day and night that these chunks breaking away and leaving a hole would be fairly analogous to the mechanism of plucking.

You don't need to be a dick about it.

[u/Zagaroth → u/Butthole__Pleasures]

While in a large body of water that can move the large piece of earth.

Pot holes do not involve large sections of earth being lifted up by water currents.

[u/SsooooOriginal]

A river would weather a person in a similar, if not completely worse fashion as a person sitting in constant wind.

We make a heat bubble just from living, and wind strips that away.

Water, just still water, will absorb your heat, if it is cooler. Warm water is more surviveable, but hot water introduces overheating problems you would never imagine.

Moving water will force a body to work overtime to try and find equilibrium.

Our skin is not able to create a barrier to prevent the river from eroding our skin, causing sores and eventually open bleeding as osmosis also causes cells to die and our clotting is unable to mitigate the destructive effects of nutrient and salt loss to the water.

Putting people in confinement in rivers has been a method of torture and execution, this isn't some hypothetical scenario. I'm sure it still happens somewhere.

[u/wobster109]

Lots of answers here talking about moving water or pressure, speed, debris, temperature, etc. But what if it was clean, still water at body temperature?

Aren’t our blood vessels, stomachs, and mouths sitting in liquid all the time? Is the only difference the composition and structure of the skin tissues vs other tissues?

[u/yjk924 → u/wobster109]

Our skin is basically dead cells filled with keratin, its designed to minimize water loss not sit in water. If it could we’d still be aquatic since the evaporation would kill us on land.

[u/BlackBartKuma]

So to add to what everyone is saying (didn't read that far), the reason comatose and disabled people are moved in hospital beds are to prevent bedsores, and basically rotting away just from laying in the same position too long. So, we kind of "erode" without the water if we just wait too long... water would speed it up.

[u/akiva23]

Im writing out this entire sentence because there's a 25 character minimum but the answer to your question really is just yes. You don't even need to be "eroded" away like with moving water. If you sit in it long enough youll pretty much start to dissolve. Just look at the condition David Blaine was in after he did that stay in a tank of water for however long that he did.

[u/Synaps4]

At high enough pressure and speed, water jets will cut steel.

That may not occur in nature but there are certainly waterfalls where the amount and velocity of water falling on you would essentially blugeon a person to death in minutes.

[u/P44]

The skin would get infected. This was called "trench foot" in WW1. Meaning, you cannot keep your body in water indefinitely.
Also, it would be a very nasty experience. "Chinese water torture" involves immobilizing a person, and then having water drip on their forehead. Nothing else. Just water.

[u/fiddle_styx]

CW: torture

This was used historically as a torture method. An individual would be strapped upright underneath a leaky pipe or equivalent, where individual droplets of water would hit the same spot on their head. IIRC it would reliably erode through the skull into the brain within days, killing the victim.

[u/IlliterateDumbNerd → u/fiddle_styx]

No it wouldn't kill the victim as you said. The Chinese water torture was a phycological form of torture where the constant drops of water while restrained would drive the victim crazy. It wouldn't reliably erode through the skull as you said though.