Concussion (kon-KUH-shun) is the most common type of traumatic brain injury * (TBI). It is caused by violent shaking or a direct or indirect blow to the head or body that temporarily affects brain function.

Annie Hits the Slope

Illustration of the head and brain, depicting the areas of the brain most vulnerable in a concussion. The frontal lobe regulates reasoning, planning, parts of speech and movement, emotions, and problemsolving.

Illustration of the head and brain, depicting the areas of the brain most vulnerable in a concussion. The frontal lobe regulates reasoning, planning, parts of speech and movement, emotions, and problemsolving. The temporal lobe is concerned with perception and recognition of auditory stimuli (hearing) and memory. Broca's area is important in the production of written and spoken language.
Illustration by Electronic Illustrators Group. © 2016 Cengage Learning®.

The next day, Annie's head still hurt, and she felt dizzy and nauseous. Her mom took her to the doctor, who asked about the accident and her symptoms. He had her follow his penlight with her eyes and asked her to walk a straight line. Annie was diagnosed with a mild concussion. The doctor ordered complete rest—for her brain as well as her body. Annie was to stay home from school until she had no symptoms for an entire day. For the first day, she was to do no homework—not even reading. The second day, if her symptoms were gone, she could try reading for a short time, but if any symptoms returned, she was to stop for another day. Annie stayed on the sofa, dozing or half-listening to the TV. By the end of the week, she could do homework for an hour without a headache. Within two weeks, she was back on the slopes, but skiing cautiously and only for one hour at a time. And she had a new helmet because the impact may have damaged her old helmet.

What Is Concussion?

Concussion is the jarring of the brain against the skull with sufficient force to cause temporary changes in brain function. The force can be a sudden acceleration and/or deceleration that shakes or shifts the brain or a rotational force that twists the brain. For example, a knockout punch causes a boxer's head to accelerate sharply, and hitting one's head in a fall can cause a rapid deceleration. The actual injury is usually on the opposite side from the impact. It is not known exactly how a concussion affects brain cells, but it appears to involve chemical changes. A rotational injury may actually shear nerve fibers in the brain. During the period of abnormal functioning from a concussion, the brain cells remain very vulnerable to a second injury. Thus, although a single concussion usually resolves on its own without lasting effects, a second blow to the head before full recovery from even a very mild concussion can cause a serious condition called second-impact syndrome * that can have long-lasting or fatal consequences.

Concussions are caused by a direct blow or impact to the head or indirect impact to the head from an injury elsewhere in the body. Most concussions occur during high-speed motor-vehicle collisions or while playing sports. They are also caused by falls and by shock waves from explosions. Thus, military combat and contact sports—especially boxing, football, and hockey—are major risk factors for concussions. Cyclists, horseback riders, skateboarders, and skiers—as well as basketball, baseball, and soccer players—are at risk of concussion from falls and collisions. Fights and industrial accidents are other causes of concussion. Even swimmers may be at risk from slamming their head into the wall of the pool while backstroking. Young children and the elderly are at particular risk of concussion from falls.

Brain abnormalities associated with “punch-drunk” syndrome or dementia pugilistica * * (CTE)—associated with the thousands of concussions suffered by professional football players over the course of their careers.

How Common Are Concussions?

Concussions are very common, but many concussions go unrecognized and untreated. Although motor-vehicle accidents are responsible for about half of all head injuries, there are an estimated 1.6 to 3.8 million TBIs associated with sports and recreation in the United States every year; the majority of these are concussions or other mild TBIs. Young children, older teens, and people over age 65 suffer the most concussions, with adolescent and young-adult males at highest risk. Repeated concussions are far more common than previously recognized in sports such as football and hockey, and they regularly occur during practices and drills, as well as in competition. Studies have shown that about one out of every five high-school football players suffers a concussion or more serious TBI, at some point. Furthermore, repeated concussions and other TBIs are among the most common injuries of modern warfare. Large numbers of veterans of the wars in Iraq and Afghanistan suffer from long-term and permanent consequences of concussion.

How Do People Know They Have a Concussion?

In the past, a concussion was defined as a temporary loss of consciousness from minor head trauma. However, in 2013, the American Academy of Neurology broadened the definition to include various other symptoms, with or without loss of consciousness. Temporary unconsciousness occurs if the impact affects consciousness centers in the brainstem * ; however, most concussions do not cause loss of consciousness. Unconsciousness that lasts more than a few minutes is indicative of a more serious TBI.

Concussion symptoms vary greatly depending on the severity, the affected areas of the brain, and the specific changes in brain cell function. Thus, no two concussions are identical. Symptoms can be physical, cognitive * , and/or emotional and may include:

  • Temporary disorientation of time and place
  • Feeling dazed or “foggy”
  • Confusion
  • Slow responses to questions
  • Memory problems or loss (amnesia), especially of events immediately before and after the concussion
  • Poor attention or inability to concentrate
  • Emotional symptoms such as anxiety, nervousness, sadness, depression, irritability, or other intense, inappropriate, or unusual feelings
  • Mood or behavior changes
  • Symptoms of even mild concussion may appear or worsen one or two days after the injury. Often, symptoms only become apparent with increased activity. Symptoms can last for days, weeks, or even months. The severity of symptoms appears to be influenced significantly by:

    How Do Doctors Diagnose and Treat Concussion?


    Loss of consciousness is a medical emergency. Immediate emergency assistance is also required if symptoms such as headache or confusion are severe or worsening, if the injured person is vomiting or having seizures, or if the pupil of one eye is larger than that of the other eye. However, signs and symptoms of concussion can be so subtle as to go unnoticed by both the injured person and bystanders. Furthermore, confusion or memory loss can interfere with a concussed person's awareness of injury. Therefore, whenever there is a blow to the head, the person should stop all activity immediately and inform someone. Parents, coaches, coworkers, and bystanders should be familiar with the signs and symptoms of concussion so they can recognize them in others and seek immediate medical advice. The injured person should not be left alone and should not drive.

    The doctor will ask the patient or companions about the accident, the patient's work and sports history, and any previous head injuries. A neurologic exam will assess pupil size, vision, sensations, strength, reflexes, balance and coordination, and memory and concentration. Injuries from concussion are not visible on x-rays, magnetic resonance imaging (MRI), or computed tomography (CT or CAT) scans of the skull or brain, which is one reason why the high incidence of concussions went unrecognized for so long.


    Concussions are treated with complete physical and mental rest until the brain has healed. Patients should avoid all activity, even reading, until all symptoms have disappeared. Returning to activities too soon can worsen symptoms, prolong recovery, and put the patient at risk for second-impact syndrome. Patients should be checked during the night after a concussion but not awakened unless there is a problem such as abnormal breathing. Loud noises, bright lights, and drugs and alcohol should be avoided. Some symptoms, such as irritability, may be treated with relaxation techniques. Since concussed people may have difficulty assessing situations and since post-concussive symptoms can increase with activity, return to activity must be gradual and monitored by a medical professional.

    In general, doctors prescribe one to five days of complete rest following a concussion. However, a 2015 study of concussed 11- to 22-year olds concluded that prolonged rest following an acute concussion may cause undue focusing on symptoms and slow recovery: patients prescribed strict rest for five days reported more daily post-concussive symptoms and longer recoveries than those who rested for only 24 to 48 hours.

    Once the patient is free of symptoms, normal activities are resumed in a stepwise manner as prescribed by the doctor. If any symptoms reappear, the activity should cease, and the patient should rest for at least 24 hours. Once symptoms have again disappeared, activities can resume at the first step or at the step previous to the one that resulted in symptoms. Examples of steps include:


    With proper rest, most people recover from mild concussions within one or two weeks without lasting problems. Young children and teens may take longer to recover, and sometimes memory problems last for months. Severe concussion or a history of previous concussions prolongs recovery. Undiagnosed concussion can lead to serious, long-term problems. Studies of concussions in contact sports indicate that the risk of a second concussion is greater than the risk of the first concussion.

    Steps for Returning to Play

    Since recovery from concussion is different for everyone, a doctor must advise when a concussed athlete can return to play. Players cannot return on the day of an injury that causes any symptoms of concussion. Players may not return for several weeks following a concussion that involved memory problems or loss of consciousness. Following a severe concussion, an athlete may not be allowed to return for a month—or even longer if it was a repeat concussion. Guidelines for children are as follows, with each step taking at least one day:

    Second-impact syndrome from even a minor blow to the head can cause rapid brain swelling and severe brain damage or death. People with frequent concussions are also at increased risk for depression and early onset of mild cognitive impairment. Frequent concussions in boxers and football and hockey players can cause chronic progressive disorders including dementia pugilistica, Parkinson's disease * , post-traumatic dementia * , and chronic traumatic encephalopathy (CTE). CTE can only be definitively diagnosed by examination of the brain after death, but symptoms, which generally become apparent at ages 40 to 50, can include:

    As many as 60 percent of people with mild TBIs develop post-concussion syndrome * (PCS), with a range of symptoms that can last for months or years. People with an undiagnosed concussion, severe concussion, or concussion that is not properly managed are at higher risk for PCS. PCS is defined as symptoms that persist for at least three months following concussion, including:

    Occasionally concussion causes a subdural hematoma—a blood clot or collection of blood on the surface of the brain from a torn blood vessel. Acute subdural hematomas from serious head blows can be fatal. However, even minor concussions—especially in the elderly—can cause chronic subdural hematomas, in which blood seeps out slowly over days or weeks, with symptoms similar to those of concussion but also possibly including slurred speech or seizures.

    Can Concussions Be Prevented?

    Awareness of the signs and symptoms of a concussion is important for the prevention of long-term consequences, especially from repeated concussion. As of 2016, preseason neurologic exams were becoming routine in sports such as football, in order to establish a baseline for evaluating future concussions. In 2010, the National Football League (NFL) adopted new rules for evaluating potential concussions and benching at-risk players. The NFL's USA Football youth development program introduced Heads Up Football to teach players to keep their heads up and lead with their shoulders when tackling. Children and teens should be taught about concussive injuries and told to inform an adult whenever they have experienced any blow to the head. The Sport Concussion Assessment Tool (SCAT) is a standardized assessment for signs and symptoms of sports-related concussion, including balance, coordination, and cognition. It is designed for coaches and parents and is available as a smart-phone app.

    See also Brain injuries • Sports Injuries: Overview


    Books and Articles

    Elliot, Clark. The Ghost in My Brain: How a Concussion Stole My Life and How the New Science of Brain Plasticity Helped Me Get It Back. New York: Viking, 2015.

    Laskas, Jeanne Marie. Concussion. New York: Random House, 2015.

    Rothman, Steven M. “America's Concussion Obsession: Commentary.” New York Times (December 22, 2015): A27.


    American Academy of Family Physicians. “Concussion.” . (accessed April 5, 2016).

    National Center for Injury Prevention and Control, Division of Unintentional Injury Prevention. “HEADS UP to Youth Sports.” Centers for Disease Control and Prevention. (accessed April 5, 2016).

    Parachute. “CONCUSSION TOOLKIT: Concussion Questions and Answers.” (accessed April 7, 2016).


    Brain Injury Association of America. 1608 Spring Hill Rd., Ste. 110, Vienna, VA 22182. Telephone: 703-761-0750. Fax: 703-761-0755. E-mail: Website: (accessed April 5, 2016).

    Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636 (800-CDC-INFO). Website: (accessed April 5, 2016).

    Parachute. 150 Eglinton Ave. E, Ste. 300, Toronto, ON, Canada M4P 1E8. Telephone: 647-776-5100. Toll-free: 888-537-7777. E-mail: Website: (accessed April 14, 2016).

    * traumatic brain injury (TBI) is a common injury to the brain from a bump, blow, jolt, or shaking, most often from motor-vehicle accidents, sports injuries, or combat; concussions are the most common type of TBI.

    * second-impact syndrome is characterized by the more severe—potentially fatal—signs and symptoms from a second concussion sustained before the brain has recovered from an initial concussion.

    * dementia pugilistica (dih-MENsha pyu-jeh-LIS-the-kah) is a neurologic disorder characterized by impaired movement, speech, and cognition, which affects boxers who have experienced repeated concussion or other head injuries.

    * chronic traumatic encephalopathy (CTE) is an ultimately fatal neurodegenerative disease with cognitive impairment and dementia caused by repeated brain injuries such as concussion.

    * brainstem is the part of the brain that connects to the spinal cord and controls basic functions, including consciousness, breathing, and blood pressure.

    * cognitive is conscious intellectual activity, including thinking, imagining, reasoning, remembering, and learning.

    * seizures (SEE-zhurs), also called convulsions, are sudden bursts of disorganized electrical activity in the brain that interrupt its normal functioning, often leading to uncontrolled body movements and sometimes a temporary change in consciousness.

    * Parkinson's disease is a neurologic disorder characterized by tremor, muscular weakness and rigidity, and impaired walking.

    * dementia (dih-MEN-sha) is a loss of mental abilities, including memory, understanding, and judgment.

    * post-concussion syndrome (PCS) is a condition in which signs and symptoms of concussion persist for at least three months following the injury.

    Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

    (MLA 8th Edition)