What causes cte

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Last updated: April 4, 2026

Quick Answer: CTE is a progressive degenerative brain disease associated with repeated head trauma, such as concussions and subconcussive blows. It is believed to be caused by the accumulation of abnormal tau protein in the brain, which disrupts normal brain function and leads to cell death.

Key Facts

CTE is diagnosed posthumously, meaning it can only be definitively identified after a person has died.
Repeated head trauma is the primary risk factor, with the duration and severity of exposure playing a significant role.
Symptoms can include memory loss, confusion, impaired judgment, impulse control problems, aggression, depression, and suicidal behavior.
The abnormal tau protein found in CTE is distinct from the tau seen in Alzheimer's disease, though both involve tau pathology.
While contact sports like American football and boxing are strongly associated with CTE, it can also affect military veterans and others with a history of head trauma.

What is CTE?

Chronic Traumatic Encephalopathy (CTE) is a neurodegenerative disease that affects the brain. It is characterized by a progressive decline in cognitive, emotional, and behavioral functions. The hallmark of CTE is the presence of abnormal tau protein deposits, known as tauopathies, that accumulate in specific patterns within the brain. These protein deposits disrupt the normal functioning of brain cells, leading to their degeneration and death over time.

What Causes CTE?

The primary and most well-established cause of CTE is repeated head trauma. This trauma can take several forms:

Repetitive Head Impacts

This includes both:

Concussions: A concussion is a traumatic brain injury (TBI) caused by a bump, blow, or jolt to the head, or by a hit to the body that causes the head and brain to move rapidly back and forth. While a single severe concussion can potentially contribute, it's the cumulative effect of multiple concussions that is most strongly linked to CTE.
Subconcussive Blows: These are impacts to the head that do not result in immediate symptoms of a concussion. However, repeated subconcussive blows, such as those experienced by athletes in contact sports during every practice and game, are now understood to be a significant contributor to CTE. The sheer number of these impacts over years can lead to the same pathological changes seen in those with a history of diagnosed concussions.

The Role of Tau Protein

While the exact mechanisms by which head trauma leads to CTE are still being researched, the leading theory involves the abnormal accumulation of a protein called tau. In healthy brains, tau protein helps stabilize the internal structure of neurons (nerve cells). In CTE, tau undergoes changes and begins to clump together, forming neurofibrillary tangles. These tangles disrupt the transport system within neurons, eventually leading to cell death. The pattern of tau accumulation in CTE is distinct from that seen in other neurodegenerative diseases like Alzheimer's disease, although both involve tau pathology.

Genetic Predisposition

Emerging research suggests that genetic factors may also play a role in an individual's susceptibility to developing CTE after head trauma. Certain gene variations, particularly in the APOE gene, might increase the risk of developing CTE or influence the severity of the disease. However, head trauma remains the essential trigger, and genetics likely modifies the risk or progression rather than being a sole cause.

Other Potential Factors

While less understood, other factors like age at the time of first head trauma, the duration and intensity of exposure to head impacts, and potentially other environmental or biological factors might influence the development and severity of CTE.

Who is at Risk?

Individuals who have experienced repeated head trauma are at the highest risk for developing CTE. This includes:

Athletes: Particularly those in contact sports such as American football, boxing, ice hockey, rugby, and soccer. The cumulative nature of hits sustained over a career is a major concern.
Military Personnel: Veterans exposed to blast injuries and combat-related head trauma.
Victims of Physical Abuse: Individuals who have experienced repeated assaults involving blows to the head.

Symptoms of CTE

The symptoms of CTE typically do not appear until years or even decades after the repetitive head trauma has occurred, often appearing in late middle age. The disease is progressive, meaning it worsens over time. Symptoms can manifest in several categories:

Cognitive Impairment: Memory loss, difficulty with planning and organization, impaired judgment, and trouble with executive functions.
Mood and Behavioral Changes: Increased impulsivity, aggression, irritability, mood swings, depression, anxiety, and sometimes suicidal ideation or behavior.
Motor Symptoms: In later stages, individuals may develop problems with coordination, gait, and speech, similar to Parkinson's disease.

It is important to note that CTE can only be definitively diagnosed after death through examination of brain tissue. However, based on clinical symptoms and a history of head trauma, clinicians can make a probable diagnosis in living individuals.

Research and Diagnosis

The study of CTE has advanced significantly in recent years, largely due to the pioneering work of researchers like Dr. Bennet Omalu. While definitive diagnosis remains post-mortem, ongoing research is exploring potential biomarkers and imaging techniques that might allow for earlier and more accurate diagnosis during life. Understanding the causes and mechanisms of CTE is crucial for developing effective prevention strategies and treatments for this debilitating condition.