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Overview of concussions

A concussion is a type of brain injury that results from trauma. Concussions are also sometimes called also sometimes called minor traumatic brain injuries or MTBIs.


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Depending on severity, concussion signs can be very subtle. Your concussion symptoms may start immediately or appear gradually (within hours or days) from the time of a head injury.


Common concussion symptoms include:

  • Confusion or feeling like your brain is in a fog
  • Difficulty with memory
  • Dizziness
  • Fatigue
  • Headache
  • Light or noise sensitivity
  • Nausea or vomiting
  • Personality changes, irritability, or depression
  • Problems with concentration
  • Ringing or buzzing in the ears (tinnitus)
  • Sleep problems

If you or a loved one have experienced a severe head injury, see a doctor as soon as possible, even if you don’t have symptoms.


The skull protects the soft, vulnerable brain tissue inside. A concussion is caused when the body or head sustains a blow strong enough to cause the brain to move suddenly and forcefully around in the skull. This movement can “bruise” brain tissue, damage brain cells, nerves, and blood vessels, and create chemical changes in the brain.


Concussions are usually caused by direct blows to the head, falling, violent hits to the body, and whiplash injuries. The most common scenarios involve:

  • Automobile-related injuries
  • Physical assault
  • Accidents and falls
  • High-impact sports such as football, wrestling, and skiing


Concussions can be classified based on their severity. Mild concussions may cause no symptoms, while severe concussions may cause significant damage to brain function. Here’s how they are defined, by grade:

  • Grade 0: Results in a minor headache that resolves quickly
  • Grade 1: Results in a brief 1-minute disorientation with no loss of consciousness; may cause a feeling of being dazed or stunned
  • Grade 2: Results in a headache, disorientation lasting longer than one minute, and sometimes other symptoms such as confusion, dizziness, irritability, and amnesia
  • Grade 3: Results in brief loss of consciousness for 1 minute and similar symptoms to Grade 2
  • Grade 4: Results in loss of consciousness lasting longer than 1 minute

Some researchers also classify concussions based on the type of symptoms and location of damage to the brain, including categories for mood, cognitive disability, headaches, vision problems, and loss of coordination.

Risk factors

Young children are at higher risk of concussion due to the size of their heads relative to their bodies as well as lack of coordination, compared to adults. Young adults are also at higher risk due to more frequent risky behaviors.


While it’s not always possible to avoid concussions, some factors may put you at higher risk. For example:

  • Use of cognitive function-inhibiting substances like alcohol and recreational drugs
  • Participation in high-risk sports such as football, rugby, skiing, rock climbing, skydiving, wrestling, and soccer
  • Exposure to domestic abuse or violence
  • If you have a condition that affects balance and coordination, increasing the likelihood of falls
  • Previous concussions


While a concussion is usually accidental and not preventable, you can limit you or your child’s risk of head injury by:

  • Wearing helmets and all appropriate safety gear, especially for children
  • Avoiding risky behavior, especially if alcohol or other substances are involved
  • Using caution when engaging in high-risk activities such as sports, mountaineering, and driving
  • If you have a previous concussion, limiting your activity and returning to everyday activities only with a doctor’s approval

The information contained in this article is meant for educational purposes only and should not replace advice from your healthcare provider.