A concussion is a significant blow to the head that may result in unconsciousness (see also concussion - first aid).

Causes, incidence, and risk factors

A concussion may result from a fall in which the head strikes against an object or a moving object strikes the head. Significant jarring in any direction can produce unconsciousness. It is thought that there may be microscopic shearing of nerve fibers in the brain from the sudden acceleration or deceleration resulting from the injury to the head.

The length of unconsciousness may relate to the severity of the concussion. Often victims have no memory of events preceding the injury or immediately after regaining consciousness with worse injuries causing longer periods of amnesia.

Often the maximal memory loss occurs immediately after the injury with regaining of some memory function as time passes. Complete memory recovery for the event may not occur.

Bleeding into or around the brain can occur with any blow to the head, whether or not unconsciousness occurs. If someone has received a blow to the head, observe closely for signs indicating possible brain damage.

Things to watch for include repetitive vomiting, unequal pupils, confused mental state or varying levels of consciousness, seizure-like activity, weakness on one side of the body or the inability to wake up (coma). If any of these signs are present, contact your health care provider promptly.


  • Loss of consciousness after a blow to the head  
  • Amnesia of events surrounding the injury

Emergency signs:

  • Persistent unconsciousness (coma)  
  • Altered level of consciousness (drowsy, hard to arouse, or similar changes)  
  • Persistent confusion  
  • Convulsions  
  • Repeated vomiting  
  • Unequal pupils  
  • Unusual eye movements  
  • Muscle weakness on one or both sides  
  • Gait or walking abnormalities

Signs and tests

A neurological examination may show abnormalities.

Tests that may be performed include:

  • Head CT  
  • MRI of the head


An initial “baseline” neurological evaluation by a health care worker determines appropriate treatment for an uncomplicated concussion. If a blow to the head during athletics leads to unconsciousness, a trained person must determine readiness for continued participation and timing for return to play.

In this situation, if a child or young adult has lost consciousness, that person should not resume athletics for a period of 3 months. Studies have shown that there is an increased rate of brain injury and occasionally death in people who have had a previous concussion with unconsciousness.

Concussion complicated by bleeding or brain damage must be treated in a hospital.

Expectations (prognosis)

Full recovery is expected from an uncomplicated concussion, although prolonged dizziness, irritability, headaches, and other symptoms may occur.


  • Intracerebral hemorrhage  
  • Brain injury

Calling your health care provider

Call your health care provider if anyone has a Head injury that produced unconsciousness, or a Head injury without unconsciousness produced symptoms that caused concern.

Go to the emergency room, call the local emergency number (such as 911), or contact your health care provider immediately if emergency symptoms develop.


Attention to safety, including the use of appropriate athletic gear, such as bike helmets and seat belts, reduces the risk of Head injury.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.