Young people may take longer to recover after their second or third concussion, a new study suggests.

Researchers typically believe the average athlete needs up to two weeks to stop having symptoms - such as headaches and memory problems - after a concussion.

But in the new study, children and young adults who had just suffered their second concussion in the last year took an average of 35 days to get back to normal.

"We have to be cautious in terms of after two weeks, if you still have symptomatic athletes, that you're not trying to hurry them back," said Dr. Paul Comper, a concussion researcher from the University of Toronto.

"The most important piece of information that comes out of this study is, if you've had prior concussions, the 10- to 14-day (recovery) thing may be completely out the window," Comper, who wasn't involved in the new study, told Reuters Health.

"For you, it might be a month."

He said the findings aren't totally surprising - it's clear that multiple head injuries are a bad thing - but they give doctors more information to pass on to their young patients after a concussion.

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