I noticed that blood comes off of skin very easily, but a marker won’t, and vice versa, marker comes off some products, but blood won’t. What’s the deal?
Deuce232: Hi guys.
Just a quick reminder about [rule #3](https://www.reddit.com/r/explainlikeimfive/about/rules#). I expect a lot more comments explaining how to remove blood stains. Those don’t explain the difference between skin and other materials so they don’t follow [rule #3](https://www.reddit.com/r/explainlikeimfive/about/rules#).
Your skin is fairly smooth, and is waterproof. When you draw on your arm in marker, the ink is carried from the tip to your skin by a solvent, like propyl alcohol, this solvent quickly dries. The solvent isn’t water, so it penetrates more deeply into the keratinized layer of skin. This leaves the ink on the top of your skin, and a little will get INSIDE your skin (I’m talking in microns) this is why when you wash it off, most of it, the stuff on the surface, comes off fairly easily. It isn’t water soluble, so you have to scrub and use soap, but it comes off. Then you always have a little left, the stuff INSIDE the very outside layer. Which you have to scrub hard to get off, you’re mostly just scrubbing off that layer.
For blood, it can’t get inside your skin, so it just dries on the surface. It’s also water soluble, so it’s easier to get off. The color is also from red blood cells, they’re much larger than ink molecules, but the blood just stays in the cracks of your skin that are harder to clean.
Think of a rope, the brown kind you see on ships in movies.
Thread isn’t that much different, just smaller.
Ink will stain the fabric just easily as blood. The solvent spreads the ink into the fabric through capillary action and that’s why when you draw on a white shirt with marker, you get the bleed where you aren’t marking, the ink is traveling down the thread.
Blood interacts with the threads in a similar way. Cotton will absorb water, so blood will absorb onto the thread just like ink. It will go into all the little nooks and crannies of the thread, and while red blood cells are bigger than the ink, they’re small enough to get to the very inside of the thread.
Then you try to wash the blood out, the red blood cells are inside that thread, they’re trapped now, they flow in, but can’t flow out. When you wash it, the red blood cells pop, leaving the red color behind, which is still trapped, stuck to individual cotton fibers now.
That’s why you can wash out *some* of the blood, it’s the blood on the surface of the thread, but you can’t wash the blood that’s on the inside of the thread.
Edit: I avoided talking about prune fingers because it’s contentious and irrelevant to this ELI5.
Prune fingers are better at grabbing while underwater, but is it due to the absorption of a small amount of water on the exterior surface of your skin? Or is it due to the body increasing the porosity of the capillaries at the skin on your fingers that causes the swelling? It’s currently being investigated and I have yet to see conclusive results from either side.
However, it’s irrelevant for this conversation. If you put your hand in a bowl of water, how long does it take to get prune fingers? How often are you floating your hand in blood?
If I put a droplet of blood on your arm, it will bead up and you can just brush it off. Or, you can take a cloth, and the cloth will absorb the blood.
So for this conversation, skin is waterproof.
Edit 2: a couple people have mentioned that those with nerve damage don’t get prune fingers, which supports skin being waterproof and that prune fingers are from a biological response. I haven’t heard of this before, so I won’t comment on it beyond saying that it’s compelling proof.
That prune fingers is due to absorption of water by the skin was probably not something a scientist tested. It is a completely logical and sound thing for someone to assume, and even if skin is waterproof, that you *eventually* absorb *some* water is still reasonable.
These kinds of facts are very common, no one thinks to test them, there really isn’t any reason to, until there is. That prune fingers is due to a biological response could be a very important fact for science, it can help teach us about localized responses, how local conditions are sensed, how the brain analyzes the information, and many other things.
This is why I question everything, if it hasn’t been tested, then it is only a hypothesis, not a fact. Also, not to trust anyone, always read the literature XD
BrokeBellHop: It’s not about the blood, it’s about the material the blood is getting on. Clothes are very prone to stain in general due to the fabrics involved. The fabric will absorb the blood the same way it absorbs water, soda, wine, etc. You skin isn’t absorbent like that.
bezmiegs: Have you tried cleaning larger amounts of dry blood from human skin? It requires a lot of rubbing and some cleaning agent, I wouldn’t call it “very easy”. Liquid blood is quite effortless to remove though.
Source: am a medical professional.
theCumCatcher: materials like fabric have many pores and crevices that the blood can get into.
when the blood coagulates, it undergoes a chemical change that hardens it in place. once tangled with many fibers and …’cured’, it’s nearly impossible to get out. this is because, kinda like glue, your blood is designed to ‘freeze’ in place to physically block cuts in your skin when it is damaged.
Now consider your skin, it is a wall to protect you from the outside down to the cellular level. It even has some complex self-cleaning mechanisms in the pores.
Outside of hair and pores, blood doesnt really have much to grab onto. but, alas, your skin isnt perfect. once blood is dried on, it’ll find any little cracks and folds and stick in them, requiring some scrubbing.
Source: I’ve modeled the reactions involved in coagulating blood for my job.
YeOldeButtPirate: There’s a lot of reasons, but the basic answer is porosity.
Imagine clothing or fabric as a sponge–lots of little holes for stuff to fill. Blood soaks into it easily.
If the clothing is a sponge, your skn is closer to wood. Still porous, can still absorb things, but not nearly as easily as a sponge.
Permanent markers, on the other hand, have ink particles that are much smaller than red blood cells–therefore, they can squeeze through smaller holes. In our wood vs sponge analogy, the permanent marker will have an easier time sticking to wood than the blood did. It also uses alcohol as a solvent which dries more rapidly than water, and so you also get the ink drying on the surface. Leaving blood on your skin long enough for it to dry will do the same thing.
As for why blood sticks better to some things despite this, it’s because blood also has a clotting mechanism that ink particles in a sharpie don’t. After drying, the blood may clot up and stick to a surface more firmly, where the ink particles are less sticky. That’s why if you’ve got a dry bloodstain on a white shirt, draw with a sharpie on it, and wash it over and over the sharpie should fade faster than the bloodstain–the blood sticks better, and is harder to remove. It’s just harder to soak in in the first place
_fatcheetah: Blood comes off of clothes if washed with cold water. Hot water actually makes the blood stains permanent.
It’s a matter of what is being used to remove the stain. To remove a permanent marker stain, alcohol, being a favorable solvent, is a good alternative. Same way (cold) water for blood.
What happens with hot water is that the biomolecules inside blood do get dissociated into simpler components which are not very affine(soluble) with water.
radicalelation: I’d imagine it’s due in part because blood is mostly water, while markers tend to be mostly some kind of chemical, depending on which. Most are solvents, I believe.
Water soaks nicely into absorbant material and proteins, like blood plasma, don’t come out all that well. Our skin doesn’t absorb water that well.
Markers dye the upper layer of the skin, as solvents like alcohols have an easier time getting in, so it takes until it’s shed to go away, unless you use something like acetone to actively remove it. Fabrics also happily absorb solvents, and get dyed by the color that comes with it.
I’m sure someone more knowledgeable will have a better answer though and I am eagerly awaiting to learn.
drmike0099: Blood contains a complex molecule called heme, which contains iron that gives it the red color. Heme is what carries oxygen in your blood.
In most fabrics, the blood cells can get in between the individual fibers. When washed in hot water, the heme breaks down and reacts with the fabric, becoming chemically bound to it and creating a stain. Always wash blood in cold water because it doesn’t react very much at low temperature.
On skin, there’s nothing for the blood to get “between”, and when the cells break, nothing for the heme to bind to. Therefore, relatively easy to wash off.
roaming_art: It all comes down to “like likes like”. Blood is extremely polar due to the high water, albumin and heme/iron content. Cotton fibers are also polar molecules. This is also why jeans and white t-shirts retain so much water when soaked, unlike polyester and nylon fabrics. However your skin, is actually covered in oil, which is extremely hydrophobic and repels polar molecules.
Shawnmeister: TLDR: Blood wasn’t made to adhere. Ink is. Sticking means adhering to a certain extent. Skin isn’t like fabric which is porous (fabric is more porous) and absorbent. In fact, skin does to its very best effort, the exact opposite of being absorbent.
Every composition settles on every surface differently.
Blood & Ink will stain clothes easily. This is due to fabric being very porous and absorbent.
Ink is made to stick and adhere to whatever surface it finds itself on to the best of its ability thus it being able to settle on glass or bare steel but being easily wiped off.
Blood isn’t like ink. It won’t stain glass or bare steel well because it wasn’t made to stick like ink is.
Our skin then, isn’t made to absorb liquids well. If it was, we’d be prone to more dangers than we are right now (also why many hazardous materials got removed from lead and ink) and this results in liquids like blood not sticking well on skin but liquids like ink which is made to stick, sticks. No surface is ever smooth and that’s pretty much how sticking works.
IamDonatella: There doesn’t seem to be a good answer yet, so I’ll take a common person’s crack at it. Honest answer? Hell, I don’t know 😂 But here’s what I found after like 20 minutes of googling. Maybe someone can elaborate.
Skin serves the function of being a barrier. Your skin is made up of a multitude of components, including cholesterol and ceramides. These create a proper ‘seal’ from the outside world. Think of it like a biological, squishy Saran Wrap.
Can’t link on mobile because I’m at work and yada yada, but according to the Journal of investigative dermatology, volume 126, issue 6, pages 1316-1322, published June 2006, it was found that 40nm particles deeply penetrated epidermal langerhans cells and the follicular epithelium of vellus hair openings. However, particles of 750 or 1,500 nanometers did not.
Red blood cells contain hemoglobin, which is a transport molecule for oxygen in the blood. Hemoglobin also happens to be a pigment, giving red blood cells their name, and (from what I understand) blood its red color.
The size of a single red blood cell is 8 micrometers. This means that red blood cells cannot enter the follicles of the skin because they’re too big.
So.. yeah. Blood doesn’t stain the skin because the pigment is too large to enter the skin.
Also, you have to keep in mind that ink isn’t just one thing. There’s all *kinds* of inks, and their vehicles vary. A lot of ink vehicles contain specific binders, whereas blood doesn’t.
So yeah. Hope this helps! 🙂
bearpics16: Dried blood is very hard to get off of skin. It can take a bit of scraping. And blood on your tongue? That’s going to be there a while.
When blood coagulates, the proteins and other stuff in the blood interconnect and becomes very sticky and adherent. Blood likes to cling to hair, especially the tiny fuzz on people’s faces that you don’t even realize is there. It doesn’t bind to bare skin as well because it’s covered in oils. Basically the force binding blood together is stronger than the force binding to skin.
Fun fact, in the dental field when patients are conscious, we sometimes refer to blood as “rbc glue” or “red glue” because of how adherent it is. Like “don’t suction that rbc glue out of the socket”, or “wipe that red glue off the crown before it sticks”
RoxanneJefferson2300: A bloodstain is orange after you wash it 3 or 4 times in a tub but that’s normal…. Ain’t it, Norman?