Over the past few years, newspaper headlines containing the word "concussion" have become disturbingly common. Much of the time, coverage has focused on professional athletes. But concussion—which can occur when force is applied to the head, with or without impact—affects people of all ages. Among 15- to 24-year-olds, sports are second only to motor vehicle accidents as the leading cause of concussion, according to the Centers for Disease Control and Prevention. More than one million athletes experience a concussion each year in the United States.

In response, the American Academy of Neurology (AAN) has released an evidence-based guideline for evaluating athletes with concussion. This new guideline, which replaces the 1997 AAN guideline on the same topic, has been endorsed by a broad range of athletic, medical, and patient groups, including the National Football League Players Association, the Child Neurology Society, the National Association of Emergency Medical Service Physicians, the National Association of School Psychologists, the National Athletic Trainers Association, and the Neurocritical Care Society.

"Among the most important recommendations the AAN is making is that any athlete suspected of experiencing a concussion immediately be removed from play," says co-lead guideline author Christopher C. Giza, M.D., with the David Geffen School of Medicine and Mattel Children's Hospital at UCLA and a member of the AAN. "We are recommending that concussion be assessed in each athlete individually. There is no set timeline for safe return to play."

Extra caution should be taken with athletes of high school age and younger, as evidence shows that they take longer to recover from a concussion than college athletes.

"If in doubt, sit it out," said lead study author Jeffrey S. Kutcher, M.D., a sports neurologist with the University of Michigan Medical School in Ann Arbor and a member of the AAN. "Being seen by a trained professional is extremely important after a concussion. If headaches or other symptoms return with the start of exercise, stop the activity and consult a doctor. You only get one brain; treat it well."

However, while an athlete should immediately be removed from play following a concussion, there is insufficient evidence supporting absolute rest, according to the authors.

The guideline was developed by reviewing all available evidence related to concussion in sports published between 1955 and June 2012. In recognition that scientific study and clinical care for sports concussions involves multiple medical specialties, a broad range of expertise was incorporated in the author panel. The authors analyzed more than 9,000 scientific studies to develop the guideline, and at least two authors independently analyzed and graded each study on the strength of its evidence.

Visit the complete collection of Neurology Now articles on concussion and traumatic brain injury. The AAN's new app, Concussion Quick Check, can help coaches and athletic trainers quickly recognize the signs of concussion. Available for the iPad, iPhone, and Android devices, the app can be found in the iTunes store or the Google Play store. More information is available from the AAN Sports Concussion Resources.

What the New AAN Concussion Guideline Says

• Among those sports evaluated in the studies, the risk of concussion is greatest in football and rugby, followed by hockey and soccer. The risk of concussion for young women and girls is greatest in soccer and basketball.
• An athlete who has a history of one or more concussions is at greater risk for being diagnosed with another concussion.
• The first 10 days after a concussion appears to be the period of greatest risk for being diagnosed with another concussion.
• There is no clear evidence that one type of football helmet can better protect against concussion over another kind of helmet. Helmets should fit properly and be well maintained.
• Licensed health professionals trained in diagnosing and managing concussion should look for ongoing symptoms (especially headache and fogginess), history of concussions, and younger age in the athlete. Each of these factors has been linked to a longer recovery after a concussion.
• Risk factors linked to long-term neurologic problems in professional athletes include prior concussion, longer exposure to the sport, and having the apoE4 gene.

Signs and Symptoms of a Concussion

• Headache and sensitivity to light or sound
• Changes to balance, coordination, reaction time
• Changes in memory, judgment, speech, or sleep
• Loss of consciousness or a "blackout" (happens in less than 10 percent of cases)

Some of the Key Features of the AAN's New Concussion Quick Check App

• Common signs and symptoms of concussion
• What to do if the athlete appears to have a concussion
• When it is okay for the athlete to return to the game
• Where to find a neurologist near you
• State laws on concussion
• The AAN new evidence-based guideline for diagnosing, treating and managing sports concussion