Children who suffer a concussion may have symptoms that begin later, and linger for weeks, after an injury.
Researchers at Boston Children's Hospital studied over 200 concussions.
The most common problems after a head injury, like headache and dizziness, usually fade within two weeks.
However, many children developed emotional effects, like frustration and irritability, after the physical symptoms were gone.
Experts recommend keeping injured children out of school for a few days after a head injury, allowing their body and minds to heal.
Meanwhile, more and more people are showing up to emergency rooms for injuries, like concussions.
University of Pittsburgh researchers found that in 2010 there were an estimated 2.5 million E.R. Visits for traumatic brain injuries, a 29% increase from 2006.
Children younger than 3 years old and adults older than 60 had the largest increase in these rates.
Researchers attribute the increase to a number of factors, including increased awareness and diagnoses.