A concussion is a form of brain injury produced when a force to the head or body causes the brain to move rapidly within the skull. It is often described in clinical settings as a mild traumatic brain injury, but the term covers a range of severity and symptoms. For concise background see brain injury and general information about the brain. A concussion typically follows a direct blow or rapid acceleration–deceleration of the head, for example a head impact in a fall or collision.

Common causes and settings

Concussions occur in many environments. Frequent causes include motor vehicle collisions, slips and falls, assaults and participation in contact sports, notably in sports such as football. Any incident in which the head receives a sudden force or the body experiences a violent shake can produce a concussion; broadly these events are classed as accidents or traumatic events.

Symptoms and clinical features

Symptoms vary in type and duration. Typical early features include headache, dizziness and cognitive changes; many people also report sleep disturbance, emotional changes and sensory problems. Commonly reported symptoms are listed below:

  • Headache or pressure in the head (headache).
  • Transient confusion, memory difficulty and slowed thinking.
  • Balance problems, light or noise sensitivity, blurred vision.
  • Excessive tiredness or lack of energy (fatigue).
  • Brief loss or alteration of consciousness in some cases (loss of consciousness).

Many concussions are brief and symptoms resolve within days to a few weeks. Persistent or worsening signs — increasing headache, repeated vomiting, seizures, progressive drowsiness, a one-sided weakness, or unequal pupil size — are medical emergencies because they may reflect bleeding within the skull (intracranial bleeding).

How concussion is diagnosed and evaluated

Diagnosis relies on clinical history and examination. Healthcare providers ask about the mechanism of injury, loss of memory for the event, and current symptoms. Standardized checklists and brief cognitive tests are commonly used to document deficits. Imaging (CT or MRI) is not routine for every concussion but is reserved for cases with concerning neurological signs or to exclude complications such as intracranial hemorrhage.

Treatment, recovery and return-to-activity

Initial management emphasizes physical and cognitive rest for a short time, followed by a gradual, supervised return to normal activities. Symptom-limited activity is encouraged rather than prolonged complete inactivity. Treatment is supportive: analgesics for pain, sleep hygiene, and therapies for vestibular or visual disturbances when needed. In sports, structured "return-to-play" protocols help guide safe resumption of training. Most people recover fully within weeks; a minority experience prolonged symptoms sometimes called post-concussion syndrome.

Prevention and notable distinctions

Prevention focuses on reducing risk in common settings: wearing a properly fitted helmet during cycling and some sports, using seat belts in vehicles, improving fall-safety measures, and applying sport-specific rules and protective strategies. It is important to distinguish concussion from more severe traumatic brain injury (TBI) which involves structural brain damage and longer-term impairment. Repeated concussions over time, particularly without full recovery between injuries, raise concern for cumulative effects and warrant extra caution.

Concussions have been recognized in medical writings for centuries and the word itself derives from terms meaning to "shake" or "strike together." Modern clinical practice emphasizes prompt assessment, avoidance of high-risk activities while symptomatic, and individualized rehabilitation if symptoms persist. For further practical resources and guidance see sports and medical guidelines and general references such as brain injury, brain health pages, and condition-specific advice at specialty sites head impact, motor vehicle collisions, contact sports, football, traumatic brain injury, bleeding, headache, fatigue, loss of consciousness, accidents and protective equipment guidance helmet.