A new study released today in the online edition of the journal Pediatrics finds children may take longer to recover from a concussion if they received another blow to the head in the past.

Researchers studied 280 children and young adults between the ages of 11 and 22 treated for concussions at Boston Children’s Hospital over a 12-month period.  Patients who never had suffered from a concussion took about 12 days to recover.

In contrast, patients who had a single concussion in the past took about 24 days to recover.  Among patients who had endured multiple blows to the head in the past, the recovery time was 28 days.  And among patients who has suffered more than one concussion or head blow within the year, the recovery time was even higher at about 35 days.

“It’s been part of the medical lore, this idea that concussions are ‘bad’ and having a repeat concussion within a short amount of time is bad,” Dr. Keith Yeates told Health Day. This new research confirms the danger of repeated concussions. Dr. Yeates is chief of pediatric psychology and neuropsychology at Nationwide Children’s Hospital in Ohio.

Both Yeates and lead researcher Dr. Matthew Eisenberg of Boston Children’s Hospital support children’s participation in sports and exercise.  But Dr. Eisenberg told Health Day that if a child has more than one concussion playing the same sport, parents might consider some other sports or activities.

Dr. Eisenberg told USA Today that concussions are of particular concern in children because doctors do not know how the injury will effect a developing brain or what, if any, the long term impact might be.

A concussion—in which the brain is jarred or shaken inside the skull–can also happen off the field through a fall or another type of injury.  An injured person may act confused or complain of a headache, dizzyness, fatigue, or ringing in the ears.  And the symptoms may appear later rather than at the time of injury.  Rest and careful monitoring are the main tools for treating a concussion, according to the Boston Children’s Hospital Sports Medicine web page.

Earlier this year, CBS News reported on new concussion guidelines issued by the American Academy of Neurology.  The main message?  When in doubt, sit it out, according to Dr. Jeffrey Kutcher, one of the authors of the new guidelines and associate professor of neurology at the University of Michigan Medical School.

If you suspect a concussion, always seek a doctor’s care.