When former NFL star Aldon Smith passed away in June 2026 at age 36, it reignited conversations about the long-term impact of professional football on brain health. To help find answers, his family is donating his brain to researchers at Boston University to test for chronic traumatic encephalopathy (CTE), a progressive brain condition linked to repeated head impacts.

While scientists cannot confirm whether Smith had CTE until the examination is complete, his story underscores the ongoing effort to understand how playing football can affect athletes long after their careers end.

Why did Aldon Smith retire?

Aldon Smith entered the NFL in 2011 and quickly became one of the league’s most dominant pass rushers. His career included standout seasons with the San Francisco 49ers, but multiple suspensions, legal issues and personal challenges interrupted his time in professional football. Smith last appeared in an NFL game during the 2020 season and officially retired in 2023, per ESPN. After retirement, he focused on mentoring younger athletes and helping them navigate the pressures of professional sports.

How many NFL players have CTE?

No one knows exactly how many former NFL players have had CTE because the condition can currently be confirmed only after death through a brain examination. However, researchers at Boston University reported finding CTE in 345 of 376 former NFL players whose brains were donated for study, representing approximately 91.7% of that research group. Scientists caution that donated-brain studies may not reflect the entire NFL population, but the findings highlight a significant connection between repetitive head impacts and CTE.

What’s happening in your body

CTE is a neurodegenerative disease linked to repeated blows to the head and repetitive brain trauma. Boston University notes that the condition is characterized by the buildup of an abnormal protein called tau, specifically phosphorylated tau (p-tau), within the brain. Over time, these protein deposits spread through different brain regions and interfere with normal brain function.

Researchers have found that larger amounts of p-tau are associated with more severe cognitive, behavioral and functional symptoms. As the disease progresses, individuals may experience problems involving memory, decision-making, mood regulation, impulse control and daily functioning.

Causes of CTE

The primary cause of CTE is repeated head trauma over an extended period. Contrary to popular belief, a person does not necessarily need to suffer multiple diagnosed concussions to develop the disease. Researchers believe that repeated sub-concussive impacts (hits that do not cause obvious symptoms) may also contribute to brain injury over time.

Football remains the sport most commonly associated with CTE, but the disease has also been identified in athletes who participated in boxing, hockey, soccer, rugby, wrestling and other contact sports. Military veterans exposed to blast injuries may also face increased risk.

Scientists believe cumulative exposure is particularly important. The more years a person spends experiencing repetitive head impacts, the greater the likelihood that abnormal tau proteins may accumulate in the brain. According to Boston University researchers, cumulative force from head trauma appears to play a significant role in determining risk.

Health risks and complications

CTE has been associated with a wide range of neurological, psychiatric and behavioral complications. Symptoms often develop years or even decades after an athlete’s playing career ends.

Individuals with CTE may experience memory loss, confusion, difficulty concentrating, impaired judgment and executive function problems. Some develop depression, anxiety, impulsive behavior, aggression or emotional instability. Others experience progressive cognitive decline that can eventually resemble dementia.

Researchers have also linked advanced stages of the disease to significant functional impairments that affect employment, relationships and daily living. Family members often report personality changes, increased irritability and difficulties with decision-making.

What to do about CTE symptoms

Anyone experiencing persistent neurological or psychological symptoms after repeated head injuries should seek medical evaluation. While no cure currently exists for CTE, early recognition may help improve quality of life and address symptoms.

Treatment often focuses on managing specific concerns. Cognitive rehabilitation may help with memory and attention problems. Mental health counseling can address depression, anxiety, irritability and mood changes. Physicians may prescribe medications to help manage symptoms such as depression, sleep disturbances or behavioral issues.

Lifestyle changes also play an important role. Regular exercise, adequate sleep, social engagement, stress management and cardiovascular health support overall brain function. Individuals who continue to participate in contact sports should discuss risk-reduction strategies with healthcare professionals.

Can CTE be detected before death?

One of the biggest challenges surrounding CTE is that doctors still cannot definitively diagnose the disease during life. Currently, confirmation requires examination of brain tissue after death. This limitation is one reason Aldon Smith’s family chose to donate his brain for scientific study.

Researchers are actively working to change that reality. A 2024 study from Boston University’s CTE Center found a clear relationship between the amount of p-tau pathology in the brain and the severity of cognitive, behavioral and functional symptoms experienced during life. By analyzing hundreds of brains with confirmed CTE and comparing pathology with symptom histories reported by family members, researchers identified patterns that may eventually help doctors recognize the disease before death.

Scientists hope these findings will contribute to the development of diagnostic criteria, imaging tools, blood tests and other biomarkers capable of identifying CTE in living patients. Experts believe that achieving a reliable diagnosis during life could eventually enable earlier treatment and intervention. Although significant progress has been made, researchers emphasize that additional studies are needed before a definitive living diagnosis becomes available.

What to do about CTE symptoms

Dr. Diana Rangaves tells Blavity Health, “Football players often face long-term health concerns, including joint pain and head injuries. Former athletes should monitor their cognitive health and take preventive steps against conditions like CTE.”

If you are concerned about possible CTE-related symptoms, begin by documenting changes in memory, mood, thinking or behavior. Keeping a journal can help healthcare providers understand symptom patterns and progression.

A neurologist can evaluate cognitive concerns, while neuropsychologists may perform specialized testing to assess memory, attention, processing speed and executive function. Mental health professionals can provide support for depression, anxiety, irritability and emotional challenges that sometimes accompany repetitive brain trauma.

Although there is currently no treatment that reverses CTE pathology, symptom-focused care can improve daily functioning and quality of life. Ongoing research explores potential therapies that may one day target the underlying disease process itself.

When to see a doctor

You should seek medical attention if you have a history of repeated head impacts and begin experiencing persistent cognitive, emotional or behavioral changes. Symptoms that warrant evaluation include memory problems, difficulty concentrating, confusion, depression, anxiety, mood swings, impulsive behavior, aggression or unexplained personality changes.

Immediate medical evaluation is especially important if symptoms interfere with work, relationships, finances, driving or other daily responsibilities. Family members should also encourage evaluation if they observe significant changes that the individual may not recognize.

Former athletes, military veterans and others with extensive exposure to repetitive head trauma may benefit from routine neurological assessments even if symptoms seem mild. Early evaluation can help identify treatable conditions, rule out other causes and connect patients with supportive resources.

Bottom line

At this time, there is no confirmed answer to the question if Aldon Smith had CTE. His family has donated his brain for examination, but researchers have not yet released findings. What Smith’s case does highlight is the ongoing concern about the long-term effects of repetitive head trauma in football and other contact sports. Researchers continue working toward earlier diagnosis and better treatments, while families, athletes and healthcare providers remain focused on recognizing symptoms and protecting brain health.

Frequently Asked Questions

Who is most prone to CTE?

People with a history of repeated head impacts, including football players, boxers, hockey players, soccer players and military veterans are the highest risk.

Is CTE a disability?

CTE itself is not automatically classified as a disability, but its symptoms can become disabling if they significantly impair daily functioning.

Citations

Boston University School of Public Health. “New Study Could Help Diagnose CTE Before Death” https://www.bu.edu/sph/news/articles/2024/new-study-could-help-diagnose-cte-before-death/

Boston University. “Can CTE Be Diagnosed in Life?” https://www.bu.edu/articles/2024/can-cte-be-diagnosed-in-life/

Boston University CTE Center. “BU Researchers Publish Crucial Study That Could Help Diagnose CTE Before Death” https://www.bu.edu/cte/2024/02/06/bu-researchers-publish-crucial-study-that-could-help-diagnose-cte-before-death/

Boston University Annual Report. “Advancing CTE Diagnosis” https://ar.bu.edu/2024/gray-matter/cte/

Boston University. “Researchers Are One Step Closer to Diagnosing CTE During Life, Rather Than After Death” https://www.bu.edu/articles/2024/researchers-one-step-closer-diagnosing-cte/

Boston University CTSI. “Researchers Find CTE in 345 of 376 Former NFL Players Studied” https://www.bu.edu/ctsi/2023/02/06/press-release-boston-university-researchers-find-cte-in-345-of-376-former-nfl-players-studied/

National Library of Medicine. “Cognitive, functional, and neuropsychiatric correlates of regional tau pathology in autopsy-confirmed chronic traumatic encephalopathy” https://pmc.ncbi.nlm.nih.gov/articles/PMC10845638/