It is caused by the accumulation of blood under the nail after a traumatism (the most frequent one is the closing of doors)
It is very painful, and very frequently due to its symptoms some medical schools recommend that it be drained by the pediatrician or the surgeon.
We advise that the family pediatrician or an emergency room be consulted to dismiss the possiblity of bone injuries and carry out the correspondent treatment.
Ask your family pediatrician.
Concerning your children's health, the Pediatrician is irreplaceable!!