What causes hang nails?
and why do they hurt so bad?
The nail could've been broken a number of ways. Maybe you banged your hand against something.They often hurt the most the further down your nail they are. I usually keep a Band-Aid on it until the broken part grows further up and I can trim it off. Keep your nails short. Long nails are vulnerable. To make them stronger, use nail polish (if you use that) with nail enamel in it. Most nail polishes have that on the label