What repeated concussions and repeated head impacts mean for memory
How repeat concussions and smaller hits may affect memory, and ways to lower risk
Maybe you hit your head in a crash last spring. Now you are thinking about going back to your weekend soccer league. Or your teen has had two concussions in two football seasons. You lie awake wondering what a third one would do to their memory.
These worries make sense. Memory and focus problems are common after a concussion. It is natural to ask whether each new hit makes things worse.
This article covers two related questions. One is about repeated concussions, meaning injuries that caused symptoms. The other is about repeated head impacts, the many smaller knocks and headers in some sports that may cause no symptoms at all. Some answers are well supported. Some are still unknown. We will try to be clear about which is which.
Two kinds of repeat injury
Repeated concussions and repeated head impacts sound alike, but researchers study them in different ways. The advice for each one is different too.
Repeated concussions
A concussion is a brain injury that causes symptoms. Common ones include headaches, feeling foggy, trouble paying attention, and problems with short or long term memory [6]. Sleep changes, sadness and irritability can show up as well [6]. When a person has had two or more of these injuries, they have a history of repeated concussions.
Each concussion is a separate event with its own recovery. Your care team will want to know how many you have had, how each one was treated, and how long each took to settle [2]. That history helps them plan your care this time.
Repeated head impacts
Head impacts are blows to the head that happen again and again during play. Tackles in football and headers in soccer are common examples. In soccer, practice and games routinely expose players to these repeated hits through heading the ball [5].
Many of these hits cause no symptoms. You might feel fine after a header and finish the game. That is why they are hard to track, and why they worry researchers. An international panel of concussion experts said the possible long term effects of concussion and repeated hits remain a public health concern that is still being studied [2].
Why the difference matters
With a diagnosed concussion, you know when the injury happened and can track recovery from that day. With repeated impacts, there is no single moment to point to. Any effect on memory would build slowly over many seasons.
What a second concussion can mean for recovery
The CDC lists a history of previous concussions as one factor that raises the chance of a longer recovery in children [1]. Having more severe symptoms right after the injury is another [1]. The CDC also warns that a brain that has not finished healing can be harmed more easily by a new injury [1].
The 2022 international consensus on sport concussion, written by 31 panel members from nine countries, adds more detail [2]. It found that early symptoms remain the strongest sign of how recovery will go [2]. It also found that playing on after a concussion, and waiting to see a health care provider, are both linked to longer recovery [2]. Good concussion care was linked to fewer repeat concussions [2].
Put together, these findings suggest that the way each injury is handled matters, along with how many injuries you have had. A person who stops playing right away and gets checked early is in a better position than one who plays on, and that choice is usually yours to make.
What this can feel like
For memory, a second concussion can blur the picture. If you were still forgetting appointments after the first injury, it can be hard to tell which problems belong to which hit. A simple log of symptoms after each injury, with dates, can help your care team sort this out.
Second impact syndrome
Second impact syndrome is a rare emergency. It happens when a second blow to the head comes before the brain has recovered from a first concussion. The brain swells quickly [4]. A 2016 review searched the medical literature and found only 17 cases that met its strict test of two witnessed hits [4]. All 17 were male and ranged from 13 to 23 years old. Of them, 10 played American football [4]. Every person with a poor outcome, meaning death or permanent disability, was younger than 20 [4].
Experts still debate the cause. Some argue the swelling has nothing to do with the first concussion [4]. An older review described how fast swelling can lead to death, and advised that any athlete still showing concussion signs should stay out of play [7].
Get emergency care right away
Call 911 or seek emergency care immediately if you see any of these danger signs after a hit or jolt to the head [6]:
- Seizures or convulsions (shaking or twitching).
- Not recognizing people or places.
- Repeated nausea or vomiting.
- Unusual behavior, more confusion, restlessness or agitation.
- Passing out, then growing drowsy, or being unable to wake up or stay awake.
- Slurred speech, weakness, numbness or poor coordination.
- A headache that worsens and will not ease.
- Pupils of different sizes, or double vision.
- In babies and toddlers, crying that cannot be soothed, or refusing to nurse or eat.
Hits that never caused a diagnosed concussion
A football study
A 2017 study looked at 93 former high school and college football players, with an average age of about 47 [3]. Researchers could not count every hit these men took. Instead they estimated each player’s lifetime hits from his own playing history, combined with counts from earlier helmet sensor studies [3]. They called this estimate the cumulative head impact index.
The more estimated hits a player had, the more likely he was to report problems later in life [3]. Above a certain level, the risk of depression, apathy, and trouble with planning and self control nearly doubled with about 2,800 extra estimated hits [3]. For poor scores on thinking tests, the jump was much larger. Going from about 6,500 to more than 12,000 estimated hits went with a risk about 25 times higher [3].
The number of concussions players remembered predicted fewer of these problems than the hit estimate did [3]. Concussion history alone did not clearly predict poor test scores [3]. This hints that the total load of hits may matter, including hits that caused no symptoms.
Soccer studies
A large Scottish study compared 7,676 former professional male soccer players with 23,028 men from the general population [5]. The groups were matched for birth year and the type of area they lived in [5]. Over time, 5.0% of the former players were diagnosed with a neurodegenerative disease, a group of illnesses in which brain cells are lost, compared with 1.6% of the comparison group [5].
Risk differed by position. Defenders had the highest risk, about five times that of the comparison group [5]. Goalkeepers did not show a clear increase [5]. Players whose careers lasted more than 15 years also had about five times the risk [5]. The authors read this pattern as a sign that risk grows with years of exposure to things outfield players face more often [5].
An earlier study by the same research team found that former professional players in Scotland were about 3.5 times as likely to die of these diseases [5]. The rise ranged from about double for Parkinson disease to about five times for Alzheimer disease [5].
What about amateur players?
The 2022 consensus statement also reviewed studies of former athletes. Former amateur athletes, mostly American football players, were not at higher risk of depression or suicide [2]. Former male amateur athletes were also not at higher risk of cognitive impairment, which means a decline in thinking skills, or of neurological disorders [2]. Former professional American football players, by contrast, had higher death rates from neurological disease and dementia [2].
So the strongest warning signs in the research come from people who played at the highest level for many years. Most weekend players and school athletes do not fit that profile.
Why head impact exposure is so hard to measure
Nobody keeps a lifetime tally of every tackle or header. Researchers have to estimate. Estimates bring error. The authors of the football study said measuring repeated hits is hard partly because it depends on what players report about themselves [3]. Their method also assumed that players took part in both games and practices [3].
Other limits run through this research:
- The football study used volunteers who learned about it online or by word of mouth. The authors said this may cause self selection bias [3].
- The same authors warned that their group should not be seen as representing all athletes [3].
- That study measured players at one point in time, so it could not prove the hits caused the problems [3].
- The soccer study had no direct information on head impacts or brain injuries, so it relied on position and career length [5].
- All the soccer players were men born up to 1969, and whether risk stays high for later generations is unknown [5].
- The consensus statement says most studies of former athletes could not account for many factors that matter, including genetics [2].
Crash survivors face an extra hurdle, because recalling decades of sports history is even harder when your memory is not what it was. Bring whatever records you have, such as old team rosters, school sports forms or medical notes, to your appointments.
What is known and what is still uncertain
The table below sorts the main questions about repeat injuries into what is better supported and what remains open.
Comparison compiled by Safety Behind the Wheel Foundation
What the research shows about repeat injuries
| Question | Better supported | Still uncertain |
|---|---|---|
| Do earlier concussions affect recovery? | A history of concussions is linked to longer recovery | How much each extra injury adds for one person |
| Does playing on after a hit matter? | Playing on and late care are linked to longer recovery | The safe timing for each person |
| Is second impact syndrome real? | Rare cases of deadly swelling in young athletes | Whether the first concussion causes the swelling |
| Do years of pro play raise later risk? | Higher rates of brain disease in former pros | Whether this applies to amateurs or newer players |
| Do hits without symptoms add up? | One study tied estimated hits to later problems | Accurate hit counts; cause and effect |
| Can CTE be diagnosed in life? | CTE is a brain tissue finding, not a clinical diagnosis | Whether CTE causes specific symptoms |
Sources: CDC [1]; Amsterdam consensus statement [2]; Montenigro et al. [3]; McLendon et al. [4]; Russell et al. [5].
CTE stands for chronic traumatic encephalopathy, a pattern of changes found in brain tissue. The consensus statement says these changes are not a clinical diagnosis [2]. When strict criteria are used, these changes are rare, both in brain banks and in samples drawn from the general community [2]. It is not known whether these changes cause specific mental health or neurological problems [2]. Studies of former athletes with CTE also cannot measure risk or show cause and effect, because of how they are designed [2].
In 2021, researchers published the first criteria for a separate condition called traumatic encephalopathy syndrome [2]. The consensus statement describes it as a new clinical diagnosis, which means doctors would make it in a living person [2]. Another article in this series looks at CTE and dementia in more depth.
If you were hurt in a crash and also play a contact sport
Plenty of people who have a concussion in a crash also play or coach a sport. Those two parts of life can stay in separate boxes. Your doctor may not know you play rugby on Sundays. Your coach may not know about the crash.
The consensus statement says a player’s concussion history, how each injury was managed. Recovery time should all be noted [2]. A crash injury belongs in that history, even though it happened off the field.
Imagine a 27 year old office worker who was rear ended on her commute and had a concussion. Six weeks later she feels mostly fine and wants to rejoin her soccer team. Her doctor cleared her for work but never asked about soccer. Her coach heard nothing about the crash. Neither person had the full story needed to plan a safe return.
Follow a stepwise return to sport
The CDC describes a six step return to play [8]. The steps are a return to regular activities, light aerobic activity, moderate activity, heavy noncontact activity, full contact practice, and then competition [8]. Each step usually takes at least 24 hours [8]. If symptoms come back, stop and contact your health care provider, then restart at the previous step once symptoms settle [8]. Return to practice only with your provider’s approval [8].
The consensus statement adds that steps with a risk of head impact should wait for full symptom recovery and approval from a health care provider [2]. It says to expect at least one week to finish the full plan, and that a full return usually happens within a month [2].
For students, school comes first. The consensus statement says student athletes should fully return to learning before an unrestricted return to sport [2]. The CDC notes that most children can go back to school within 1 to 2 days, with short term supports such as rest breaks and extra time on tests [9].
Think about driving too
Driving uses memory, attention and quick reactions. A TBI can affect each of these. Memory problems may mean forgetting where you were going or how to get there [10]. A small 2017 study tested 14 young adults in a driving simulator within 48 hours of their concussion symptoms ending [11]. They drifted out of their lane more often than 14 matched drivers without a concussion, especially on curves [11].
Teens may return to the wheel sooner than to the field. A study from Children’s Hospital of Philadelphia found that nearly half of teens seen in specialty concussion care were driving again about two weeks after the injury [12]. Few of them had gone back to sports by then [12]. Ask your care team about driving as its own question, separate from sports.
Lowering the chances of another injury
You cannot remove all risk from contact sports. Some steps do have good evidence behind them. The consensus statement reviewed prevention research and reported these results:
- Banning body checking in child and teen ice hockey cut the game concussion rate by 58% [2].
- Mouthguards were linked to a 28% lower concussion rate in ice hockey across age groups [2].
- Limits on the number and length of contact practices in American football led to a 64% drop in practice concussions [2].
- Warm up programs that train balance, strength and body control, done at least three times a week, were linked to fewer concussions in rugby [2].
The CDC’s prevention advice for sports includes enforcing the rules of the game and limiting contact practices [13]. Coaches should teach athletes not to hit others in the head or use their own head to tackle [13]. The CDC also warns families to be wary of helmet add ons that may overstate how well they prevent injury [13].
Should you stop playing?
Some people with several concussions wonder whether to retire from contact sports. The consensus statement calls this decision complex and says there is no clear evidence on which factors should make someone stop [2]. It encourages people who leave contact sports to keep up noncontact or low contact physical activity [2]. Make this decision with your care team, and know that it can change as you learn more about your own recovery.
A checklist for players, parents and coaches
Checklist from Safety Behind the Wheel Foundation
- Write down every concussion you have had, including any from a crash, with dates and how long recovery took.
- Tell your coach or athletic trainer about any head injury that happened outside sports.
- Tell your care team which sports you play and what position.
- Leave the game or practice after any suspected concussion, and do not go back that day [2].
- Wait for a health care provider’s approval before any contact.
- Wear a mouthguard in sports where one is used.
- Ask your coach how many full contact practices the team holds each week.
- Ask about driving separately, and do not assume sports clearance covers it.
Questions to ask your care team
Question checklist from Safety Behind the Wheel Foundation
- How many concussions are in my records, and does that number change your plan for me?
- Do my memory problems seem to come from this injury, an older one, or something else?
- Which symptoms should make me stop an activity and call you?
- When can I start each step of returning to my sport?
- Who will approve my return to full contact?
- Is it safe for me to drive yet, and how will we decide?
- Should I have my memory tested by a neuropsychologist?
- If I decide to stop contact sports, what other activities would suit me?
Frequently asked questions
Does every concussion take longer to heal than the one before?
Not always. A history of concussions raises the chance of a longer recovery, but it is one factor among several [1]. The consensus statement found that how strong symptoms are in the first days is the best guide to recovery [2]. Stopping play right away and getting care early are both linked to a shorter recovery [2].
Is heading a soccer ball a risk to my child’s memory?
The strongest soccer findings come from former professional men born before 1970 who played for many years [5]. Reviews of former amateur athletes have not found a higher risk of cognitive impairment, though most of those studies looked at football players [2]. It still makes sense to support rules and coaching that cut down on head contact [13].
Can a test show whether I have CTE?
Not at this time. The consensus statement says CTE describes changes seen in brain tissue. It is not a clinical diagnosis [2]. Researchers have proposed criteria for a related clinical condition, traumatic encephalopathy syndrome, but these are new [2]. If your memory is getting worse, ask your care team to look for other causes.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Repeated concussions and repeated head impacts deserve to be taken seriously. A history of concussions can slow recovery. Second impact syndrome, though rare, is a real danger for young athletes. The most worrying long term findings come from former professionals with long careers. The research behind them has real limits.
Report every head injury, including the one from the crash, to both your care team and your coach. Return to sport one step at a time, ask separately about driving, and back the rules that reduce head contact.
Sources and further reading
- 1Centers for Disease Control and Prevention. Recovery from concussion (HEADS UP). Reviewed September 2025. cdc.gov/…/recovery-from-concussion.ht…
- 2Patricios JS, Schneider KJ, Dvorak J, et al. Consensus statement on concussion in sport: the 6th International Conference on Concussion in Sport, Amsterdam, October 2022. British Journal of Sports Medicine. 2023;57(11):695-711. bjsm.bmj.com/content/57/11/695
- 3Montenigro PH, Alosco ML, Martin BM, et al. Cumulative head impact exposure predicts later-life depression, apathy, executive dysfunction, and cognitive impairment in former high school and college football players. Journal of Neurotrauma. 2017;34:328-340. doi.org/10.1089/neu.2016.4413
- 4McLendon LA, Kralik SF, Grayson PA, Golomb MR. The controversial second impact syndrome: a review of the literature. Pediatric Neurology. 2016;62:9-17. doi.org/10.1016/j.pediatrneurol.2016.03.009
- 5Russell ER, Mackay DF, Stewart K, MacLean JA, Pell JP, Stewart W. Association of field position and career length with risk of neurodegenerative disease in male former professional soccer players. JAMA Neurology. 2021;78(9). doi:10.1001/jamaneurol.2021.2403. pmc.ncbi.nlm.nih.gov/articles/PMC8329793
- 6Centers for Disease Control and Prevention. Signs and symptoms of concussion (HEADS UP). Reviewed September 2025. cdc.gov/heads-up/signs-symptoms/index.html
- 7Bey T, Ostick B. Second impact syndrome. Western Journal of Emergency Medicine. 2009;10(1). westjem.com/…/second-impact-syndrome.html
- 8Centers for Disease Control and Prevention. Returning to sports after a concussion (HEADS UP). Reviewed September 2025. cdc.gov/…/returning-to-sports.html
- 9Centers for Disease Control and Prevention. Returning to school after a concussion (HEADS UP). Reviewed August 2025. cdc.gov/…/returning-to-school.html
- 10Model Systems Knowledge Translation Center. Driving after traumatic brain injury. 2024. msktc.org/…/driving-after-traumatic-bra…
- 11Schmidt JD, Hoffman NL, Ranchet M, et al. Driving after concussion: is it safe to drive after symptoms resolve? Journal of Neurotrauma. 2017;34(8):1571-1578. doi.org/10.1089/neu.2016.4668
- 12McDonald CC, Jain D, Storey EP, Gonzalez M, Master CL, Arbogast KB. Changes in driving behaviors after concussion in adolescents. Journal of Adolescent Health. Published online December 15, 2020. doi:10.1016/j.jadohealth.2020.10.009. Summary: Penn Today, January 7, 2021. penntoday.upenn.edu/…/nearly-half-young-drivers-r…
- 13Centers for Disease Control and Prevention. Preventing concussion (HEADS UP). Reviewed September 2025. cdc.gov/heads-up/prevention/index.html
This article reflects the safety priorities of brain injury recovery and road safety education. It offers general education about repeat head injuries and is not medical advice. Guidance can change, so check official sources such as the CDC, and talk with your own care team about your situation, your sport and your driving. Reviewed October 2026.
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