Traumatic Brain Injury (TBI)

Quick answer

A traumatic brain injury (TBI) is a brain injury caused by an outside force, such as a forceful bump, blow or jolt to the head or body, or an object entering the brain.[1] Not every blow to the head causes a TBI.[1] In 2023 there were 68,663 TBI-related deaths in the United States, about 190 every day.[2]

What a TBI is

The CDC defines a TBI as “an injury that affects how the brain works.”[3] NINDS explains that some types of TBI cause temporary or short-term problems with brain function, including how a person thinks, understands, moves, communicates and acts, while more serious TBI can lead to severe and permanent disability, and even death.[1]

A TBI is one kind of head injury. Head injuries can also affect the scalp, skull, face, eyes, ears, jaw and teeth without injuring the brain. See Head injuries by area.

Mild, moderate and severe

MedlinePlus describes three levels of TBI: mild (also called a concussion), moderate and severe.[4] It notes that how much brain function is affected, and for how long, depends on how severe the TBI is, and that moderate to severe TBIs can cause life-long health problems.[4]

The CDC states that most TBIs that occur each year are mild TBIs or concussions.[3] A 2020 study in the Journal of Neurotrauma notes that 80% to 90% of patients who come to the emergency department with a TBI have mild TBI, defined as a Glasgow Coma Scale score of 13 to 15, and that fewer than 10% of that group have abnormalities on a head CT scan.[5] See Glasgow Coma Scale.

How TBI damages the brain

Focal and diffuse injury

According to NINDS, damage from a TBI can stay in one area of the brain, called a focal injury, or spread over a wider area, called a diffuse injury.[1] The types of damage usually seen include bleeding, swelling, and tearing that injures nerve fibers, which can cause inflammation and metabolic changes.[1]

Diffuse axonal injury

NINDS describes diffuse axonal injury (DAI) as one of the most common types of TBI, involving widespread damage to the brain’s white matter that can disrupt communication among nerve cells.[1]

Primary and secondary injury

NINDS notes that although brain injury often happens at the moment of impact, much of the damage related to severe TBI develops from secondary injuries that happen days or weeks after the initial trauma.[1]

Common causes

The CDC states that people most commonly get TBIs from a fall, a firearm-related injury, a motor vehicle crash or an assault.[6] Falls lead to nearly half of TBI-related hospitalizations, and older adults are more likely to be hospitalized and die from a TBI than any other age group.[6] Firearm-related suicide is the most common cause of TBI-related deaths in the United States.[6]

Learn more: Falls · Car crashes · Sports concussions · Assault

TBI by the numbers

68,663

TBI-related deaths in the U.S. in 2023[2]

214,110

TBI-related hospitalizations in 2020[2]

~50%

Share of TBI hospitalizations caused by falls[6]

The CDC notes that some groups are at greater risk of dying from a TBI or having long-term health problems after one, including service members and veterans, people living in rural areas, survivors of intimate partner violence, and people experiencing homelessness.[6]

Types of brain injuries

This page provides general information from the sources listed below. It is not medical advice and is not a substitute for evaluation by a qualified healthcare provider. In an emergency, call 911.

Sources

  1. National Institute of Neurological Disorders and Stroke. “Traumatic Brain Injury (TBI).” https://www.ninds.nih.gov/health-information/disorders/traumatic-brain-injury-tbi
  2. Centers for Disease Control and Prevention. “TBI Data.” https://www.cdc.gov/traumatic-brain-injury/data-research/index.html
  3. Centers for Disease Control and Prevention. “About Mild TBI and Concussion.” https://www.cdc.gov/traumatic-brain-injury/about/index.html
  4. MedlinePlus Medical Encyclopedia. “Traumatic brain injury.” https://medlineplus.gov/ency/article/000799.htm
  5. Okonkwo DO, et al. “Point-of-Care Platform Blood Biomarker Testing of Glial Fibrillary Acidic Protein versus S100 Calcium-Binding Protein B for Prediction of Traumatic Brain Injuries: A TRACK-TBI Study.” Journal of Neurotrauma, 2020. https://pmc.ncbi.nlm.nih.gov/articles/PMC7698990/
  6. Centers for Disease Control and Prevention. “Facts About TBI.” https://www.cdc.gov/traumatic-brain-injury/data-research/facts-stats/index.html

Sources last checked: October 11, 2026

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