Crushed Fingertip
A little blood under the nail is unlikely to benefit from treatment
When there is also a wound, more things can go wrong
Sometimes a piece of the fingeritp is lost
It's common to crush the tip of the finger in a door or between two objects.
If everything moves and works properly and the fingertip isn't unstable, then the body usually just needs time to heal.
When there is bleeding or a piece of the tip is missing, surgery might be needed and it's best to see a hand surgeon.