Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Concussion

What Is It?

A concussion is a short-term disturbance in brain function caused by a head injury. A concussion causes:

• Confusion, headache or dizziness

• Loss of consciousness lasting less than 30 minutes or no loss of consciousness at all

• Loss of memory (amnesia) lasting less than 24 hours

About 8 million people suffer head injuries in the United States each year. Less than 10% require hospitalization, and most of these people have only minor injuries. About half of all head injuries happen during motor vehicle accidents. Falls, sports and assaults cause the rest. Alcohol and drug use are major contributing factors.

Most head injuries result from direct trauma (for example, the head hitting the ground or the windshield of a car). In the elderly, serious head injuries can result from even minor falls. Injuries also can occur from rapid acceleration or deceleration, as may happen in a whiplash injury. People who injure their heads often injure their necks, too. Magnetic resonance imaging or computed tomography (CT) scans of someone with a concussion rarely show obvious signs of brain injury, although doctors believe the symptoms are caused by swelling and damage to nerve fibers in the brain. Occasionally, minor head trauma can trigger a more serious problem such as bruising of the brain tissue (brain contusion) or bleeding within the head (subdural hematoma or subarachnoid hemorrhage). Bleeding and other complications of minor head injuries appear to be more common in the elderly and in people taking blood thinners such as warfarin (Coumadin).