About Repeated Head Impacts

Key Points

  • Repeated head impacts may or may not lead to concussion symptoms.
  • Collisions while playing sports is one way a person may experience repeated head impacts.
  • Chronic traumatic encephalopathy (CTE) is a brain disease that affects how the brain works.
Animated image of a person's brain highlighted with red.


There is growing concern about the long-term effects on the brain of people who experience multiple or repeated head impacts. Repeated head impacts include not only head impacts that lead to a mild TBI or concussion, but also head impacts that do not cause the person to feel symptoms after a hit to the head. Collisions while playing sports is one way a person may experience repeated head impacts.

A CDC study found that youth tackle football athletes ages 6 to 14 sustained 15 times more head impacts than flag football athletes during a practice or game and sustained 23 times more high-magnitude head impacts (hard head impacts).

Chronic Traumatic Encephalopathy (CTE)

Chronic traumatic encephalopathy (CTE) is a brain disease that affects how the brain works. It is linked to a build-up of abnormal proteins that damage brain tissue and cause brain cells to undergo cell death.12

Research suggests CTE is associated with long-term exposure to repeated hits to the head (head impacts). There is no strong evidence that shows that getting one or more concussions (or other mild traumatic brain injuries) or occasional hits to the head leads to CTE.34 More research is needed to better understand:

  • Potential risk factors for CTE, including the role of a person's sex, genetics, medical history, and environmental and lifestyle factors.
  • How the CTE disease process begins.
  • Why some people with a history of long-term exposure to repeated head impacts develop CTE and others do not.567


Scientists are not certain what symptoms are directly linked to CTE. Family members of people who were later diagnosed with CTE reported that the person had problems with thinking, emotions, mood, suicidal thoughts and/or behaviors that became serious enough to get in the way of normal daily activities (such as social and work-related activities).578 However, having these symptoms does not necessarily mean a person has CTE. It is important to talk to a doctor if you, a family member, or friend have any questions or concerns. Treatments are available to help with many of these symptoms.

Diagnosing CTE

Currently, the only way doctors can confirm a CTE diagnosis is by checking the brain of a person after they die (also called an autopsy of the brain). Specialized doctors, called neuropathologists, look for changes in the brain in people suspected of having CTE to confirm whether or not the person had CTE, or other diseases, such as Alzheimer's Disease, vascular disease, or Parkinson's disease.7 Neuropathologists commonly find more than one disease in a brain during an autopsy of a person suspected of having CTE.9

The National Institutes of Health has supported several research studies and scientific meetings to better understand CTE and learn how to diagnose CTE while a person is alive. Most research is focused on advancing non-invasive methods to see what is happening inside the brain of a living person and to track it over time. An example includes using imaging (such as Positron Emission Tomography) to scan the brain and observe the patterns of certain proteins in different parts of the brain.


Counting CTE Cases is Difficult

Scientists do not currently know how many people have or will develop CTE in the United States. CTE has been found in the brains of some deceased contact and collision sport athletes, combat military veterans, victims of intimate partner violence, and others with and without a reported history of long-term exposure to head impacts who donated their brains for research.71011 Prior studies suggest that CTE is likely very rare.31213 This is especially true among groups of people who have an unknown or no reported history of long-term exposure to head impacts.31213


To learn more about CTE and other brain diseases:

  • Visit the National Institutes of Health website.

If you or someone you know needs to speak with a trained counselor:

  • Call the Substance Abuse and Mental Health Services Administration National Helpline at 1-800-662-HELP (4357), or text "home" to 741741
  • Call the National Alliance on Mental Illness Helpline at 1-800-950-NAMI (6264)

Contact the 988 Suicide and Crisis Lifeline if you are experiencing mental health-related distress or are worried about a loved one who may need crisis support.

The Veterans Crisis Line connects veterans, their family, or friends with qualified, caring responders:

  • Call the confidential, toll-free hotline at 988 then press 1
  • Text to 838255
  • Chat online
  1. McKee AC, Cairns NJ, Dickson DW, et al. The First NINDS/NIBIB Consensus Meeting to Define Neuropathological Criteria for the Diagnosis of Chronic Traumatic Encephalopathy. Acta Neuropathol. 2016;131(1):75-86. doi: 10.1007/s00401-015-1515-z
  2. Bieniek KF, Cairns NJ, Crary JF, et al. The Second NINDS/NIBIB Consensus Meeting to Define Neuropathological Criteria for the Diagnosis of Chronic Traumatic Encephalopathy. J Neuropathol Exp Neurol. 2021;80(3):210-219. doi:10.1093/jnen/nlab001
  3. Postupna N, Rose SE, Gibbons LE, et al. The Delayed Neuropathological Consequences of Traumatic Brain Injury in a Community-Based Sample. Original Research. Front Neurol. 2021;12. doi:10.3389/fneur.2021.624696
  4. Rivara FP, Tennyson R, Mills B, et al. Consensus Statement on Sports-Related Concussions in Youth Sports Using a Modified Delphi Approach. JAMA Pediatr. 2020;174(1):79-85. doi:10.1001/jamapediatrics.2019.4006
  5. Asken BM, Sullan MJ, DeKosky ST, Jaffee MS, Bauer RM. Research Gaps and Controversies in Chronic Traumatic Encephalopathy: A Review. JAMA Neurol. 2017;74(10):1255-1262. doi: 10.1001/jamaneurol.2017.2396
  6. Iverson GL, Gardner AJ, McCrory P, Zafonte R, Castellani RJ. A Critical Review of Chronic Traumatic Encephalopathy. Neurosci Biobehav Rev. 2015;56:276-293. doi:10.1016/j.neubiorev.2015.05.008
  7. McKee AC, Stein TD, Huber BR, et al. Chronic Traumatic Encephalopathy (CTE): Criteria for Neuropathological Diagnosis and Relationship to Repetitive Head Impacts. Acta Neuropathol. 2023/04/01 2023;145(4):371-394. doi:10.1007/s00401-023-02540-w
  8. Stern RA, Daneshvar DH, Baugh CM, et al. Clinical Presentation of Chronic Traumatic Encephalopathy. Neurology. 2013;81(13):1122-1129. doi: 10.1212/WNL.0b013e3182a55f7f
  9. Mez J, Daneshvar DH, Kiernan PT, et al. Clinicopathological Evaluation of Chronic Traumatic Encephalopathy in Players of American Football. JAMA. 2017;318(4):360-370. doi:10.1001/jama.2017.8334
  10. Danielsen T, Hauch C, Kelly L, White CL. Chronic Traumatic Encephalopathy (CTE)-type Neuropathology in a Young Victim of Domestic Abuse.J Neuropathol Exp Neurol. 2021;80(6):624-627.
  11. Suter CM, Affleck AJ, Lee M, Pearce AJ, Iles LE, Buckland ME. Chronic Traumatic Encephalopathy in Australia: The First Three Years of the Australian Sports Brain Bank. Med J Aust. 2022;216(10):530-531. doi:10.5694/mja2.51420
  12. Forrest SL, Kril JJ, Wagner S, et al. Chronic Traumatic Encephalopathy (CTE) Is Absent From a European Community-Based Aging Cohort While Cortical Aging-Related Tau Astrogliopathy (ARTAG) Is Highly Prevalent. J Neuropathol Exp Neurol. 2019;78(5):398-405. doi:10.1093/jnen/nlz017
  13. McCann H, Bahar AY, Burkhardt K, et al. Prevalence of Chronic Traumatic Encephalopathy in the Sydney Brain Bank. Brain Commun. 2022;4(4). doi:10.1093/braincomms/fcac189