eli5: How are our finger/toe nails stuck on top of our fingers/toes if they’re constantly growing out?
In: 30
It makes a kind of glue which glues down the nail to the skin. If you have ever broken a nail far enough down you will recognize this glue.
So at the front you have a bit of skin attached to the nail that also grows a bit to attach to the nail sealing the front part. (The Hyponychiuim)
The sides are folded over and form a similar seal. (Nail Folds)
The back where the nail forms is also sealed on account of continuously forming the nail (Nail matrix). Also on top by your cuticle.
The nail bed isn’t as firmly attached to the actual nail, but is shaped into a bunch of grooves running back to from that match grooves in the nail. Some new cells do grow out and attach to the nail but at a much slower rate than from the matrix in the rear so it’s not as solid a connection. That allows the nail to slide forward but not shift around like say skin over a blister would. And the seals around the edges for a vacuum seal so the nail can’t separate from the bed easily.
Though if you say smash your finger, or get a big splinter under it and blood starts pooling under there the nail can become separated and you have to wait for it to grow forward to reestablish that vacuum seal working back to front as it grows out.
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