A 14-year-old goalkeeper collides with a striker, sits on the grass for a minute, then insists she is fine. By dinner she has a headache, and the kitchen lights seem too bright. A generation ago the advice would have been strict: a dark room, no screens, no school and no friends until every last symptom was gone.
That advice has been retired. The 2023 international consensus statement on concussion in sport, written after a conference of experts in Amsterdam, concluded that strict rest until symptoms fully clear does not help recovery. In its place is a short stretch of taking it easy, followed by a gradual, watched return to daily life, then school, then sport.
The numbers are large. A 2019 CDC report found that an average of 283,000 children under 18 went to US emergency departments each year from 2010 through 2016 with brain injuries from sports and recreation. Football, bicycling, basketball, playground activities and soccer led the list. Here is how current guidance handles the first days and weeks.
What counts as a concussion
A concussion is a brain injury caused by a bump, blow or jolt that moves the brain inside the skull. In 2023 the American Congress of Rehabilitation Medicine (ACRM) published new diagnostic criteria for mild traumatic brain injury (TBI). Thirty of its 32 expert panelists agreed that “concussion” and “mild TBI” can be used as the same label when brain imaging is normal or not needed. In this article the two terms mean the same thing.
The sport consensus wrote its own short definition: a traumatic brain injury caused by a direct blow to the head, neck or body. Even that wording won only 78.6% support from the panel, below the 80% bar the group had set for consensus.
Nobody has to be knocked out
The most persistent myth is that a real concussion requires blacking out. It does not. The CDC’s 2018 guideline on mild TBI in children uses a definition, drawn from a 2004 international task force, under which confusion, disorientation, a short memory gap or another passing neurological change is enough. Losing consciousness is one possible sign, not a requirement.
Headache is the most familiar symptom, but CDC also lists dizziness, poor balance, early nausea, blurred vision and sensitivity to light or noise. Thinking can feel slowed or foggy, memory may slip, moods can turn irritable, anxious or sad, and sleep can go long, short or restless.
Timing matters as well. CDC’s HEADS UP program says signs can surface hours or even days later and are usually at their worst in the first day or two. Very young children cannot describe a headache, so parents look for changes instead: more crying or clinginess, less interest in play, eating or sleeping differently, or seeming dazed and unsteady.
The danger signs that mean 911
Most concussions heal without drama. A few head injuries hide something more serious. CDC’s adult page notes that, in rare cases, blood can collect into a clot that presses the brain against the skull. Because a concussion and a life-threatening bleed can look alike at first, CDC says the following signs call for 911 or the nearest emergency department right away, at any age:
- A headache that keeps getting worse and will not let up
- Vomiting again and again
- A seizure or convulsions
- Slurred speech, weakness, numbness or clumsiness
- One pupil larger than the other, or double vision
- Growing confusion, restlessness, agitation or strange behavior
- Failing to recognize familiar people or places
- Passing out, getting steadily drowsier, or being hard or impossible to wake
For infants and toddlers, CDC adds two more: crying that cannot be soothed, and refusing to nurse or eat.
Some people need a lower threshold for care after any knock to the head. The American College of Emergency Physicians (ACEP) says the usual decision checklists cannot reliably rule out a scan for adults taking anticoagulants, or antiplatelet drugs other than aspirin. Falls, blood thinners and brain injury in older adults are the core of the library’s traumatic brain injury article.
Why most people never need a CT scan
A CT scan of the head is very good at one job: finding bleeding, swelling and skull fractures that may need surgery. It does not show a concussion. A textbook concussion usually comes with a perfectly normal scan, which is exactly what the ACRM terminology above assumes.
CT also uses radiation, so clinicians try to scan only the people likely to have a bleed. The CDC guideline for children, which abbreviates mild TBI as mTBI, is direct: “Health care professionals should not routinely obtain head computed tomography (CT) for diagnostic purposes in children with mTBI…” It explains that radiation from head CT has been linked to a small rise in lifetime cancer risk, and that some young children need sedation to hold still, which adds its own risks.
Scans still matter for some. The same guideline notes that up to 7.5% of children seen in emergency departments with mild TBI have some injury inside the skull. The goal is to find those children without scanning everyone else, and emergency clinicians do that with decision rules built from tens of thousands of patients.
The checklists behind the decision
For children, the best known comes from the Pediatric Emergency Care Applied Research Network, or PECARN. Its 2009 study in The Lancet enrolled 42,412 children with minor head injuries at 25 North American emergency departments. About 35% got a CT, yet only 0.9% had a clinically important brain injury and 0.1% needed neurosurgery. In the validation group, almost no child the rules labeled very low risk had an important injury: none of 1,176 children under 2, and 2 of 3,800 older children.
The CDC guideline endorses validated rules such as PECARN. The factors that raise concern fall into a few groups: how the injury happened (a severe mechanism), age (under 2), what the child shows (vomiting, a blackout, memory loss, a severe or worsening headache, or reduced alertness) and what the clinician finds on the head (a suspected skull fracture, or scalp swelling anywhere other than the forehead).
For adults, ACEP’s 2023 clinical policy gave its top rating, Level A, to the Canadian CT Head Rule. The rule came from a 2001 study of 3,121 adults at 10 Canadian hospitals. Its five high-risk factors include being older than 65, vomiting more than twice, signs of a skull fracture and failing to return to full alertness within two hours. In the original study those factors caught every patient who needed neurological intervention while calling for scans in only 32% of patients.
What the brain-injury blood tests can and cannot tell you
It is easy to come away thinking there is now a blood test for concussion. That is not what the Food and Drug Administration cleared.
The tests measure two proteins made by brain cells, known as GFAP and UCH-L1. In February 2018 FDA granted a lab test run on serum from blood drawn within 12 hours of injury. In January 2021 it cleared a plasma version, still for clinical labs and still within 12 hours. In March 2024 it cleared a whole-blood version that can be run at the point of care as well as in a lab, within 24 hours of injury. All three cover adults 18 and older with a suspected mild TBI, and all three exist to help a clinician decide whether a head CT is needed.
The numbers, in plain terms
In the study behind the 2018 decision, 1,947 adults had both the blood test and a CT. The test flagged 117 of the 120 people whose scans showed an acute injury, a sensitivity of 97.5%. But its specificity was only 36.5%: it came back positive in most people whose scans were clean, so fewer than 1 in 10 positive results matched an abnormal CT. The negative result is the useful one. Among people who tested negative, 99.6% had a clean scan.
So the test answers a narrow question: how likely is an injury that a CT would show? It says nothing about whether someone has a concussion, how severe it is or when they can play again. Because a concussion usually leaves the CT normal, a negative blood test does not rule one out.
Children are a separate question. The CDC’s 2018 guideline said biomarker testing to diagnose mild TBI in children belongs in research settings. The Amsterdam consensus recommendations for children, published in Pediatrics in 2024, judged blood and imaging biomarkers to have limited clinical use so far. A University of Nebraska study began recruiting in May 2025 to test the same two proteins in children.
Rest is brief now: the first two days
Strict rest made intuitive sense: an injured brain should be left alone. But the CDC guideline notes that evidence on the timing, length and benefit of rest is limited.
The Amsterdam consensus describes relative rest instead, meaning ordinary daily activities with less screen time, starting right away and lasting up to two days. It says light physical activity such as walking is acceptable in the first 24 to 48 hours, as long as it makes symptoms no more than mildly worse. The consensus defines “mildly” in numbers: a rise of no more than 2 points on a 0-to-10 symptom scale that settles in under an hour. Cutting back on screens makes sense for the first 48 hours, the consensus adds, though the benefit may not extend past that.
The pediatric version of the consensus summed up the change in one line: “Rather than strict rest, early return to light physical activity and reduced screen time facilitate recovery.”
The CDC guideline says much the same in a federal voice: more limited activity for the first several days, then a gradual schedule that does not worsen symptoms, then a structured return to non-contact aerobic activity. Its rationale notes that rest within the first three days may help, but that staying inactive past that point may make most children feel worse. The message is not that rest is harmful. It is that rest should be short. Randomized trials of supervised early aerobic exercise sit with the library’s coverage of symptoms that outlast a month.
How the first month is laid out
This is a map of what current guidance describes, not a prescription. The pace depends on symptoms, and the clinician following the injury sets it.
- First day or two: relative rest and ordinary routines with fewer screens, while watching for the 911 signs, since CDC notes symptoms can appear hours later.
- Headache: the CDC guideline tells clinicians to offer non-opioid pain relief to children and to warn families that overuse can cause rebound headache. Which product, if any, is a question for the child’s clinician or pharmacist.
- Day 1 to 2: most children can be back at school, according to CDC, often with supports.
- The following days: light activity, then a stepwise return to sport, with no contact until a health care professional has cleared it.
- Day 10: if dizziness, neck pain or headaches remain, the Amsterdam consensus recommends cervicovestibular rehabilitation, physical therapy aimed at the neck and the inner-ear balance system. Whether to refer is the treating clinician’s decision.
- Week 4: symptoms still present meet the consensus definition of persisting symptoms. A 2024 American Family Physician summary of the consensus suggests considering a specialist referral then, or sooner if symptoms are severe.
Back to the classroom first, then back on the field
School comes before sport, and sooner than many families expect. CDC says many children go back while still having some symptoms, and its HEADS UP school page says getting students back to class can shorten recovery and lower the chance of mental health symptoms.
Supports follow the symptoms. CDC’s examples include a lighter workload focused on what matters most, extra time, fewer tests in one day, class notes, rest breaks, dimmer seating and a quiet place to work. For students whose symptoms drag on and affect schoolwork, CDC points to formal options such as a 504 plan or an individualized education program (IEP), which vary by state and district.
The Amsterdam consensus found that 93% of athletes of all ages had fully returned to learning without extra academic support within 10 days. It says students should complete their return to learning before any unrestricted return to sport.
The six steps back to sport
Each of the consensus’s six steps usually takes at least 24 hours, so the sequence lasts at least about a week. The early steps are activity limited by symptoms, light and then moderate aerobic exercise, and sport drills done alone. Steps that carry a risk of a blow to the head, such as contact practice and games, come only after a health care professional has given approval and symptoms have fully resolved. Unrestricted return typically takes up to a month; pooling the studies, the consensus estimated an average of 19.8 days.
The trade-off cuts both ways. Moving too fast risks a second injury while the brain is still recovering. Moving too slowly means weeks of isolation, missed school and lost fitness. The yardstick for moving ahead is the same as in the first days: any flare in symptoms should be mild and brief.
The laws that pull young athletes off the field
In 2009, Washington passed the Zackery Lystedt Law, the first concussion law aimed at protecting youth athletes. A 2014 account in Neurosurgery lists its key provisions, including immediate removal from a game or practice after a suspected concussion and written clearance by a concussion expert before returning.
By 2014, all 50 states and the District of Columbia had youth concussion laws built on the same principles, according to a report on Georgia’s law published that year in the Journal of Law, Medicine & Ethics. A 2018 chapter in the Handbook of Clinical Neurology identifies three parts most share: concussion education before the season, mandatory removal from play when a concussion is suspected, and clearance by a health care professional before return. The trigger is suspicion, not certainty.
Did the laws work?
Reported concussions went up after the laws, which can look like a sign that they backfired. A 2017 study in the American Journal of Public Health, covering 8,043 concussions in high school athletes from 2005 to 2016, attributed the rise most likely to better recognition and reporting. The rate of repeat concussions fell significantly starting about 2.6 years after the laws took effect.
A 2026 review in Seminars in Pediatric Neurology adds that laws like Washington’s were associated with less concussion-related health care use, though enforcement, training rules and return-to-learn policies vary widely by state.
Second impact syndrome: rare, debated, and a reason for caution
The National Institute of Neurological Disorders and Stroke (NINDS) cautions that a second concussion that follows closely on the first can occasionally cause lasting damage or prove fatal, and that recovery tends to be slower after a second or third concussion.
The specific condition called second impact syndrome, catastrophic brain swelling after a second blow, is rare and thinly documented. A 2016 systematic review turned up 338 articles but only eight case studies suitable for analysis, with imaging and confirmed signs mixed or missing. A 2001 review in the Clinical Journal of Sport Medicine argued that the evidence tying these cases to repeated concussion was not compelling, and that they are better described as diffuse cerebral swelling, a known complication of brain injury that is more common in children and teens.
In the library’s evidence terms, second impact syndrome as a distinct disease has insufficient evidence: the cases are too few and too poorly documented to define it. The caution does not depend on the label. Every state’s law requires a health care professional’s clearance before a young athlete returns, and the consensus reserves contact for athletes whose symptoms have resolved.
Two time points to remember
Concussion care now turns on two time points. In the first 48 hours, the work is watching for danger signs and keeping activity light rather than stopping it. CDC’s adult page says most people are feeling better within about two weeks.
The second time point is four weeks. Symptoms still present then are persisting symptoms under the Amsterdam consensus, and the CDC guideline for children tells clinicians to provide or refer for further assessment when symptoms have not resolved with standard care within four to six weeks. That is when the question shifts from how much to rest to what is keeping symptoms going, a shift the companion piece on lasting symptoms follows. At any point, a worsening headache, repeated vomiting, a seizure or a person who cannot be woken means 911.
Sources
- Centers for Disease Control and Prevention (HEADS UP). “Signs and Symptoms of Concussion (last reviewed September 15, 2025).” cdc.gov
- Centers for Disease Control and Prevention. “Signs and Symptoms of Mild TBI and Concussion (last reviewed September 15, 2025).” cdc.gov
- Centers for Disease Control and Prevention (HEADS UP). “Returning to School After a Concussion (last reviewed August 6, 2025).” cdc.gov
- Centers for Disease Control and Prevention (JAMA Pediatrics). “Lumba-Brown A, Yeates KO, Sarmiento K, Breiding MJ, Haegerich TM, Gioia GA, et al. "Centers for Disease Control and Prevention Guideline on the Diagnosis and Management of Mild Traumatic Brain Injury Among Children." JAMA Pediatr, 2018. PubMed. DOI: 10.1001/jamapediatrics.2018.2853.” pubmed.ncbi.nlm.nih.gov
- British Journal of Sports Medicine. “Patricios JS, Schneider KJ, Dvorak J, et al. "Consensus statement on concussion in sport: the 6th International Conference on Concussion in Sport-Amsterdam, October 2022." Br J Sports Med, 2023;57(11):695-711. DOI: 10.1136/bjsports-2023-106898.” doi.org
- Pediatrics. “Davis GA, Schneider KJ, Anderson V, Babl FE, Barlow KM, Blauwet CA, et al. "Pediatric Sport-Related Concussion: Recommendations From the Amsterdam Consensus Statement 2023." Pediatrics, 2024. PubMed. DOI: 10.1542/peds.2023-063489.” pubmed.ncbi.nlm.nih.gov
- American Congress of Rehabilitation Medicine (Archives of Physical Medicine and Rehabilitation). “Silverberg ND, Iverson GL, Cogan A, Dams-O-Connor K, et al. "The American Congress of Rehabilitation Medicine Diagnostic Criteria for Mild Traumatic Brain Injury." Arch Phys Med Rehabil, 2023. PubMed. DOI: 10.1016/j.apmr.2023.03.036.” pubmed.ncbi.nlm.nih.gov
- American College of Emergency Physicians (Annals of Emergency Medicine). “American College of Emergency Physicians Clinical Policies Subcommittee; Valente JH, Anderson JD, Paolo WF, Sarmiento K, Tomaszewski CA, Haukoos JS, Diercks DB, et al. "Clinical Policy: Critical Issues in the Management of Adult Patients Presenting to the Emergency Department With Mild Traumatic Brain Injury." Ann Emerg Med, 2023. PubMed. DOI: 10.1016/j.annemergmed.2023.01.014.” pubmed.ncbi.nlm.nih.gov
- The Lancet. “Stiell IG, Wells GA, Vandemheen K, Clement C, Lesiuk H, Laupacis A, et al. "The Canadian CT Head Rule for patients with minor head injury." Lancet, 2001. PubMed. DOI: 10.1016/s0140-6736(00)04561-x.” pubmed.ncbi.nlm.nih.gov
- The Lancet. “Kuppermann N, Holmes JF, Dayan PS, Hoyle JD, Atabaki SM, Holubkov R, et al. "Identification of children at very low risk of clinically-important brain injuries after head trauma: a prospective cohort study." Lancet, 2009. PubMed. DOI: 10.1016/S0140-6736(09)61558-0.” pubmed.ncbi.nlm.nih.gov
- U.S. Food and Drug Administration. “Evaluation of Automatic Class III Designation for DEN170045 (decision summary; De Novo granted February 14, 2018).” accessdata.fda.gov
- U.S. Food and Drug Administration. “510(k) Premarket Notification K201778, brain trauma assessment test (decision January 8, 2021).” accessdata.fda.gov
- U.S. Food and Drug Administration. “510(k) Summary K201778.” accessdata.fda.gov
- U.S. Food and Drug Administration. “510(k) Substantial Equivalence Determination Decision Summary K234143 (decision March 27, 2024).” accessdata.fda.gov
- ClinicalTrials.gov (National Library of Medicine). “Validating a Blood Test for the Detection of Traumatic Brain Injury in Children (NCT06940232).” clinicaltrials.gov
- Centers for Disease Control and Prevention (MMWR). “Sarmiento K, Thomas KE, Daugherty J, Waltzman D, Haarbauer-Krupa JK, Peterson AB, Haileyesus T, Breiding MJ. "Emergency Department Visits for Sports- and Recreation-Related Traumatic Brain Injuries Among Children – United States, 2010-2016." MMWR Morb Mortal Wkly Rep, 2019. PubMed. DOI: 10.15585/mmwr.mm6810a2.” pubmed.ncbi.nlm.nih.gov
- Neurosurgery. “Ellenbogen RG. "Concussion advocacy and legislation: a neurological surgeon's view from the epicenter." Neurosurgery, 2014. PubMed. DOI: 10.1227/NEU.0000000000000495.” pubmed.ncbi.nlm.nih.gov
- Journal of Law, Medicine & Ethics. “Cook A, King H, Polikandriotis JA. "Where do we go from here? An inside look into the development of Georgia's Youth Concussion Law." J Law Med Ethics, 2014. PubMed. DOI: 10.1111/jlme.12145.” pubmed.ncbi.nlm.nih.gov
- Handbook of Clinical Neurology. “Parsons JT, Baugh C. "The evolving landscape of policies, rules, and law in sport-related concussion." Handb Clin Neurol, 2018. PubMed. DOI: 10.1016/B978-0-444-63954-7.00025-2.” pubmed.ncbi.nlm.nih.gov
- American Journal of Public Health. “Yang J, Comstock RD, Yi H, Harvey HH, Xun P. "New and Recurrent Concussions in High-School Athletes Before and After Traumatic Brain Injury Laws, 2005-2016." Am J Public Health, 2017. PubMed. DOI: 10.2105/AJPH.2017.304056.” pubmed.ncbi.nlm.nih.gov
- Seminars in Pediatric Neurology. “Espinosa-Villagomez P, de la Torre A, Torres A. "Policy and advocacy for concussion awareness and safety." Semin Pediatr Neurol, 2026. PubMed. DOI: 10.1016/j.spen.2026.101258.” pubmed.ncbi.nlm.nih.gov
- National Institute of Neurological Disorders and Stroke. “Traumatic Brain Injury (TBI) (last reviewed March 13, 2026).” ninds.nih.gov
- Journal of Science and Medicine in Sport. “Hebert O, Schlueter K, Hornsby M, Van Gorder S, Snodgrass S, Cook C. "The diagnostic credibility of second impact syndrome: A systematic literature review." J Sci Med Sport, 2016. PubMed. DOI: 10.1016/j.jsams.2015.12.517.” pubmed.ncbi.nlm.nih.gov
- Clinical Journal of Sport Medicine. “McCrory P. "Does second impact syndrome exist?" Clin J Sport Med, 2001. PubMed. DOI: 10.1097/00042752-200107000-00004.” pubmed.ncbi.nlm.nih.gov
- American Academy of Family Physicians (American Family Physician). “Lau K. "Concussion in Sport: Recommendations From the 6th International Conference on Concussion in Sport." Am Fam Physician, 2024;110(4):435-436.” aafp.org