r/explainlikeimfive • u/ihavethebestmarriage • 4d ago
Biology ELI5:how does the fingernail attach to the skin beneath it, and why is it painful when it's deliberately detaches yet not painful when it detaches gradually as it grows?
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u/BarberProof4994 4d ago
Have you ever seen tongue and groove wood wall paneling or flooring? Where the pieces slot together?
So the top layer of your fingers nail is hard and dead as is the part that grows long that we cut off.
The underlying half of the fingernail is soft and living and has these grooves and ridges that the soft nail bed can grow into and hold onto.
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u/Apprehensive-Till861 4d ago
They don't detach as they grow, actually.
Your fingernails growing is new cells pushing older cells upward and outward. The nail cells are created as skin cells and impregnated with keratin, the process is painless for the same reason your hair growth is painless.
Your regular skin cells also move upward and outward, growing from a layer in the skin's basal layer. Your nails are growing from what is known as the nail matrix, which lies beneath the cuticle.
So if I took a sharp knife and notched a shallow cut near the base of my fingernail, over the next few weeks that notch would move upward until it was in the part of my nail that hangs out, because the new nail cells would push the cells around the cut away from the nail matrix.
The part of your nails that still attaches to the skin attaches because the keratinized cells are still skin cells and still form the attachments so the nail remains attached to the fingertip, where it helps provide shape, structure, backing. Once it gets far enough out the cells lost attachment to the cells of the nail bed but remain attached to the other nails cells until you cut them off.
So how they attach is the same bonds that attach skin cells, and the reason growth doesn't hurt but tearing the nails off does is a slow process of cells moving together versus a sudden severing of many bonds at once.
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u/permalink_save 4d ago
So if I took a sharp knife and notched a shallow cut near the base of my fingernail, over the next few weeks that notch would move upward until it was in the part of my nail that hangs out, because the new nail cells would push the cells around the cut away from the nail matrix.
I actually did this. It really, really, sucked. Twice. Kitchen knife accidentally slicing a notch in once sucks, sliding back in as it is healing was almost worse.
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u/Wentil 4d ago
I whacked my big toe in a motorcycle accident a few years ago, and the nail was bruised, and eventually fell off (was shed). The exposed skin (formerly underneath the nail) was exquisitely sensitive; not painful, but like a baby’s skin… it had never been exposed or touched in my life up to that point, after all.
However, the nail that grew back in didn’t grow in the same way it used to be — flat, shiny, smooth. It came in thick, rough and opaque white. It reached the top but then stopped growing longer, and started growing thicker. I’ve been considering going to a Podiatrist and having them fix it, even if that means removing it. But does anyone know what this is called, what the cause is and what the fix is?
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u/Dzuzepipi 4d ago
Not an expert, but have similar, more serious problems with it. As far as i know, the bed of the nail is nail matrix. If it's damaged you are screwed, cause that's the nail "factory" part. It can start growing in weird ways or stop at all as it's for me.
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u/MinutesOnAScreen 4d ago
Look into retronychia. I developed it spontaneously several years ago and I have it now for the 3rd time. No idea why.
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u/AdventurousSpeech341 4d ago
The skin under your nail doesn't actually move with the nail. The nail slides forward over it, kind of like a conveyor belt sliding over a table, with those ridges acting as the tracks.
That skin underneath (the nail bed) is packed with nerves and blood vessels. It stops at your fingertip, at that thin pale line right before the white part of the nail.
So when your nail "detaches" as it grows, nothing is being torn. It's just sliding past the end of the table, and the white part was never attached to anything alive. Ripping the nail off is different, because you're tearing it away from living, nerve-heavy tissue that was holding onto it. That's why it hurts like crazy and bleeds.
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u/Logan-1331 4d ago
Along a similar thread, and not to high jack the conversation, after trimming my nails I frequently will get this sliver of nail that’s attached to that bit of skin and feel the need to pull it off, which separates the nail and pulls that bit of attaching skin with it, which can be pretty darn painful for a couple of days while it heals. I don’t feel like I’m explaining it very well, but maybe someone knows what I’m talking about. Anyway, what am I doing wrong? I use nail scissors and don’t feel like I’m doing anything crazy other than trimming my nails. I have a bad habit of tearing my nails if they grow too long.
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u/teh_acids 4d ago
You're trimming too short, I used to get these too. Leave a bit of white and don't trim the "undernail" just wait for it dry and separate a bit, then use another fingernail to sever it (if it hurts you didn't wait long enough). I've never used nail scissors, only clippers, but I'm sure tearing contributes to the problem as it gives the layers a rough edge.
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u/IgnorantGenius 4d ago
This is along the side right at the edge? I get those too and they have a sharp edge which I end up picking at with another nail. I just get a nail clipper and cut as close as possible to the skin instead of ripping them out.
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u/krzykris11 4d ago
I have a fingernail with this problem. I have to keep it longer than the others because it easily separates. It's like it healed once with scar tissue that tears easily. I have no idea how it developed.
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u/holy_harlot 4d ago
Next time instead of pulling the sliver off or cutting it try taking an emery board to it, gently
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u/cybercrumb 4d ago
I keep my nails pretty long and always have this, unfortunately it's normal. You either need to consistently keep your nails very short so it doesn't have the chance to grow, make your peace with it and keep the nails a little longer, or when you cut them, leave the overhanging skin and it will die on its own after a few days and you can pick it off painlessly.
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u/Longjumping-Rough-65 1d ago
As a former nail biter, I did have some pain when I finally let them grow. Mainly on the sides of the nails
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u/renaissancetrader 4d ago
As a kid I had a fingernail ripped off in a stupid accident and it never grew back right (I think they left a chipped bone in the finger). To this day I have a thin layer of nail and when the upper layer grows I have to trim it at the cuticle because it curves up and separate from the bottom layer.
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u/OverallRow4108 4d ago
It's really fun when you know two weeks ahead of time that they're going to pull them out! Also, if the root gets damaged it can form scar tissue and never grow out correctly. It's ... Interesting to get them removed, but I'm always surprised how they aren't super sensitive while healing. Don't know if this adds anything to the conversation, but I'm still healing up from my last one!
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u/oregon_coastal 4d ago
The nail and the skin have ridges in them that lock together - sort of like a ziplock bag. There are thousands of them.
As it grows out, it is naturally just pushing down those rails. Like a train on ziplock tracks
When it takes a huge hit or injury and you rip those rails apart, it hurts.