Concussions, also called mild traumatic brain injury, are caused by a bump or jolt to the head. The impact causes the brain to bounce or twist, potentially damaging brain cells. Repeated concussions have been linked with a debilitating brain disease found in autopsies on some retired football players.

The guidelines from the U.S. Centers for Disease Control and Prevention, the first broad evidence-based recommendations for diagnosing and treating children’s concussions recommends

against routine X-rays and blood tests for diagnosis and reassure parents that most kids’ symptoms clear up within one to three months. The CDC’s guidelines are for concussions from all causes, including falls, sports and car accidents. They recommend rest from physical and mental activity including school and sports immediately after a concussion, gradually resuming normal routines.

At least 1 million U.S. children get concussions each year although the true frequency is unknown because there is no national effort to track them and many go untreated.