A concussion is a head injury that happens when your brain moves or twists inside your skull. Concussions are a type of traumatic brain injury. They’re some of the most common (and most commonly misunderstood) injuries that people experience.

Almost everyone’s heard of someone “getting their bell rung” or “seeing stars” after a hit. Those phrases might make it seem like concussions aren’t a big deal. And it’s true that concussions aren’t usually life-threatening. But the effects can be serious and last for days, weeks or even longer.

One concussion usually doesn’t cause permanent brain damage. But experiencing multiple concussions over a lifetime can change your brain’s structure or how it works, which can lead to severe complications and increase your risk of developing serious health conditions.

How common are concussions?

Concussions are very common injuries. Experts estimate that between 1 and 3 million people visit the emergency room with a concussion in the U.S. each year. They’re especially common in young athletes. In fact, concussions account for more than half of ER visits for kids ages 5 to 18 every year in the U.S.

Symptoms and Causes

What are concussion symptoms?

Concussions stretch and injure nerves and blood vessels in your brain. They cause chemical changes that temporarily make your brain stop working like it should. Your brain will automatically redirect all its energy to healing itself after an injury. It will send signals to your body to get you to slow down and avoid activities. That’s where concussion symptoms come from. They’re your brain’s way of telling you to take it easy while it heals.

Concussion symptoms can affect your:

• Physical body
• Cognitive function (your thinking and how your brain works)
• Sleep
• Emotions and feelings

Concussion symptoms may start right away. But some people don’t experience symptoms for hours, or even days.

Physical concussion symptoms are usually the most obvious and can include:

• Headaches or a feeling of pressure in your head
• Neck pain
• Balance problems (including dizziness)
• A feeling of lightheadedness
• Nausea and vomiting
• Double vision (diplopia)
• Blurred vision
• Sensitivity to light (photophobia)
• Hearing a ringing in your ears (tinnitus)
• Sensitivity to sounds (hyperacusis)
• Temporary loss of consciousness (fainting or passing out).

Your cognitive function is how well your brain works and controls the rest of your body. A concussion can interfere with your brain’s normal function and cause:

• Confusion
• Feeling like you’re in a fog or not like your usual self
• Trouble concentrating or focusing
• Amnesia or short-term memory loss

Your brain controls your body’s natural sleep cycles. It tells your body when to feel sleepy and when to wake up. A concussion can disrupt those normal rhythms, including making you:

• Feel drowsy or fatigued
• Have trouble falling or staying asleep
• Sleep less than usual
• Sleep more than usual

A concussion is a physical injury that can affect your mental and emotional health. Emotional concussion symptoms can include:

• Irritability
• Mood swings
• Depression or sadness
• New or increased anxiety or feeling nervous

What causes concussions?

Concussions happen when something jolts or shakes your body. If the force is strong enough, it can make your brain move back and forth or side to side and damage it. Your brain tissue is soft and squishy. It’s surrounded by cerebrospinal fluid, which acts like a liquid cushion between it and your skull. Picture a glass bowl of gelatin. If you smack the bowl hard enough, the energy passes through the glass into the gelatin and makes it jiggle.

That energy transfer is what happens when you get a concussion. A strong force hits your head, neck or body, moves through your skull into your brain and makes your brain shake or wiggle. This force can twist and damage the tiny nerves and blood vessels in your brain.

The most common causes of concussions include:

• Falls
• Motor vehicle accidents
• Bike accidents
• Physical violence like fights or assaults
• Sports injuries

What are complications of a concussion?

Concussions (especially repeated concussions) can cause some serious complications.

Post-concussion syndrome (PCS) happens when recovering from a concussion takes an unusually long time. You might experience symptoms for much longer than usual (four months, a year or even longer) after the original injury.

Other complications are rare, but can include:

• Bleeding inside your skull or brain (intracranial hemorrhage)
• Swelling in your brain (cerebral edema)
• Midline shift (your brain moving off-center inside your skull)
• Skull fractures

People who’ve experienced one concussion have an increased risk for another, more serious concussion if they return to physical activities or sports too soon. Providers call this second-impact syndrome (SIS). SIS increases your risk of severe complications like brain swelling and bleeding. SIS can be fatal.

Diagnosis and Tests