A concussion is a mild traumatic brain injury caused by a bump, blow, or jolt to the head, or a hit to the body that makes the head snap back and forth and jars the brain inside the skull. One of the most common misunderstandings about concussion is that it always involves getting knocked out; in fact, most concussions happen without any loss of consciousness at all. Concussions are common, especially among children, teens, and athletes, and while the symptoms can feel unsettling, the great majority of people recover fully within days to a few weeks with the right care. This guide explains what a concussion is, its symptoms, causes, how it is diagnosed, the treatments available, and the latest research.
What is a concussion?
A concussion is a type of mild traumatic brain injury caused by a bump, blow, or jolt to the head, or a forceful hit elsewhere on the body, that makes the head and brain move quickly back and forth. This motion can stretch brain cells and trigger chemical changes that disrupt how they communicate. Because the disturbance is functional rather than visible on imaging, a concussion is classified as mild, but its symptoms are not minor.
Concussions are among the most common brain injuries and affect people of all ages, though children, teens, and athletes in contact sports face particular risk. Contrary to popular belief, most people who have a concussion never lose consciousness; being dazed or confused is far more typical than blacking out. Most concussions resolve within days to a few weeks, and recognizing the injury early helps guide safe recovery.
Symptoms of a concussion
Concussion symptoms generally fall into four categories: physical, cognitive, emotional, and sleep-related. Not everyone has every symptom, and severity varies from person to person. Symptoms can appear right away, but they are often delayed by hours or even days and may shift over the following days, so it is worth watching for new or worsening signs even if a person seemed fine at first.
| Category | Common symptoms |
|---|---|
| Physical | Headache, nausea, dizziness, balance problems, blurred vision, fatigue, and sensitivity to light or noise |
| Cognitive | Feeling mentally foggy or slowed down, trouble concentrating, and memory problems |
| Emotional | Irritability, sadness, and increased anxiety |
| Sleep-related | Sleeping more or less than usual, and trouble falling asleep |
Because these changes can be subtle or easy to blame on stress or tiredness, it helps to view a concussion as a pattern across four areas rather than one sign. Anyone with a suspected concussion should be watched closely for a day or two, since worsening symptoms can mean the brain needs more time or, rarely, that something more serious is happening.
Emergency warning signs: call 911
A small number of head injuries involve bleeding or swelling inside the skull that needs emergency treatment. Call 911 or go to the nearest emergency room right away if you or someone you are watching develops any of the following:
- One pupil larger than the other
- Repeated vomiting
- A headache that keeps getting worse
- A seizure or convulsion
- Slurred speech
- New weakness or numbness in an arm or leg
- Increasing confusion or agitation
- Difficulty waking up
Some of these signs, such as slurred speech and one-sided weakness, overlap with recognizing the sudden warning signs of a stroke, which is one reason emergency staff take them seriously regardless of cause. They can appear soon after the injury or develop over the following hours, so anyone with a head injury should be watched closely for at least the first day.
What causes concussions and the risk factors
Falls are the leading overall cause of concussion, especially among young children and older adults, followed by sports, motor vehicle crashes, and assaults. A fall itself sometimes has an underlying medical trigger, and figuring out why someone fell matters as much as treating the head injury; distinguishing the seizures of epilepsy as the cause of a fall, for example, changes the treatment plan and helps prevent a repeat.
Certain factors raise the risk of concussion or of a slower recovery. Children, teens, and older adults are generally more vulnerable to head injury, and athletes in contact sports such as football, hockey, and soccer face repeated head impacts. A previous concussion, especially before fully recovering from it, raises the risk of another and tends to lengthen recovery time.
How a concussion is diagnosed
A concussion is diagnosed clinically: doctors rely on the injury history, a neurological exam, and standardized testing rather than a scan. The exam checks vision, balance, coordination, and reflexes, while brief cognitive tests assess memory and concentration. Tools such as the Sport Concussion Assessment Tool (SCAT6) and its office counterpart SCOAT6 help clinicians score symptoms on the sideline or at a follow-up visit.
| Diagnostic step | What it involves |
|---|---|
| Injury history | How the head or body was struck and what happened right afterward |
| Neurological exam | Checks of vision, balance, coordination, and reflexes |
| Cognitive testing | Brief tests of memory, concentration, and recall |
| Standardized tools (SCAT6, SCOAT6) | Structured symptom scoring, used on the sideline or at a follow-up visit |
| Head CT scan | Reserved for patients meeting validated decision-rule criteria for possible bleeding or a skull fracture |
Imaging is not part of a routine concussion evaluation, since a concussion is a functional injury that typically will not show up on a CT or MRI. A head CT is used selectively, guided by validated decision rules, such as the PECARN criteria in children, that flag the few patients whose findings suggest possible bleeding or a skull fracture needing urgent treatment. This spares most patients unnecessary radiation while still catching injuries needing immediate care. When symptoms raise questions beyond a typical concussion, further imaging may aim at ruling out a brain tumor or another cause.
A newer tool here is an FDA-cleared blood test measuring two proteins, GFAP (glial fibrillary acidic protein) and UCH-L1 (ubiquitin C-terminal hydrolase-L1), released after a brain injury. Drawn within about 12 to 24 hours in adults with suspected mild traumatic brain injury, it accurately identifies patients without a lesion visible on CT. Its role deserves precision: a negative result lets a clinician confidently skip a head CT, but the test does not diagnose a concussion, and a positive result does not confirm one either — it rules out the need for a scan, not the concussion itself, which remains a clinical diagnosis. Interpreting the reference ranges and flags on a lab report can help you understand any result in context.
Treatment options for a concussion
There is no medication that cures a concussion; treatment focuses on giving the brain conditions to heal while avoiding a second injury. Guidance has moved away from prolonged rest in a dark, quiet room. Instead, most people benefit from a brief period of relative rest, about 24 to 48 hours, followed by a gradual, symptom-guided return to activity, adding a little more each day rather than waiting until every symptom is gone.
| Approach | Role |
|---|---|
| Brief relative rest (24-48 hours) | Gives the brain a short window to settle before activity resumes |
| Gradual, symptom-guided activity | Increases activity in small steps, staying below the level that triggers symptoms |
| Sub-symptom-threshold aerobic exercise | Light-to-moderate exercise started early, kept below symptom-triggering intensity |
| Return-to-learn plan | A stepwise increase in school or work tasks and screen time, adjusted to symptoms |
| Return-to-play protocol | A supervised, stepwise increase in exertion, with medical clearance required before contact activity resumes |
Returning to school, work, and sports follows a similar stepwise pattern, called return-to-learn and return-to-play, with each step adding a bit more demand only once the previous one does not worsen symptoms. One rule has no exceptions: nobody returns to play the same day as a suspected concussion, even if symptoms seem to clear quickly, since the brain stays vulnerable to a second injury while healing. Full return to contact sports requires clearance from a qualified clinician, and lingering symptoms such as dizziness or trouble focusing can respond to vestibular or physical therapy.
Living with a concussion and long-term outlook
Most people recover within a few days to about a month, and a return to school, work, and recreation becomes possible as symptoms fade. A smaller number continue to have symptoms for months or longer, a pattern often called persistent post-concussive symptoms or post-concussion syndrome. Headache is one of the most common lingering complaints, sometimes resembling the throbbing pain of a migraine, along with dizziness, fatigue, and trouble concentrating. These symptoms are real and treatable, and a clinician experienced in concussion care can help pinpoint which problem is driving them.
Repeated concussions and head impacts, even ones that do not each rise to a diagnosed concussion, are an area of active research and concern in contact sports. Athletes with a history of multiple concussions tend to take longer to recover and may face a higher chance of long-term problems with thinking and mood. The strongest evidence linking heavy, repetitive head impacts to chronic traumatic encephalopathy, or CTE, which can resemble the progressive memory and thinking changes of dementia, comes from former professional athletes with many years of exposure; CTE can currently only be confirmed after death. To be precise, this association is real, but current evidence does not show that concussions raise depression or suicide risk in former amateur athletes, and a causal link to typical youth sports has not been proven.
Latest scientific advances in concussion research
According to PubMed-indexed research, the most influential recent update is the 6th International Consensus Statement on Concussion in Sport, published after an international panel’s 2022 meeting in Amsterdam; it refined the definition of concussion, introduced updated tools including SCAT6, SCOAT6, and CRT6, and reinforced individualized, symptom-guided return-to-play protocols rather than a fixed timeline (Patricios et al., 2023). What this means for you: a single fixed one-week-off rule is gone, replaced by a staged framework tailored to each person’s symptoms. A multicenter study across 16 European emergency departments tested the GFAP and UCH-L1 blood test in 1,438 adults with mild traumatic brain injury and found it correctly identified 98.3 percent of patients with no CT lesion, with a 99.1 percent negative predictive value (Lagares et al., 2024). What this means for you: a single blood draw can safely help rule out the need for a CT scan in most adults with a mild head injury, sparing unnecessary radiation.
Treatment research has advanced too: a 2025 systematic review pooled 9 randomized controlled trials involving 346 people with concussion and found that high-to-moderate intensity aerobic exercise, especially started early in the acute phase, improved concussion-related symptoms, with most trials rated high quality (Alashram et al., 2025). What this means for you: light, symptom-guided aerobic activity soon after injury, rather than waiting until symptoms fully resolve, is increasingly backed by trial evidence, though exercise should stay below the level that triggers symptoms.
Glossary of key concussion terms
| Term | Definition |
|---|---|
| Concussion | A mild traumatic brain injury caused by a bump, blow, or jolt that makes the brain move rapidly inside the skull. |
| Mild traumatic brain injury (mTBI) | The broader medical term for a concussion: a temporary disruption in brain function, not lasting damage. |
| Post-concussion syndrome | Concussion symptoms, such as headache or trouble concentrating, that persist for weeks or months longer than usual. |
| SCAT6 | The Sport Concussion Assessment Tool, a standardized exam used on the sideline or in the office. |
| GFAP/UCH-L1 blood test | An FDA-cleared blood test measuring two brain-injury proteins, used to help decide whether a head CT is needed. |
| Return-to-play protocol | A supervised, stepwise increase in activity used to safely clear an athlete to resume sports. |
| Chronic traumatic encephalopathy (CTE) | A neurodegenerative condition linked to repeated head impacts, currently diagnosable only after death. |
Frequently asked questions about concussions
Do you have to lose consciousness to have a concussion?
No. Losing consciousness happens in only a minority of concussions. Far more common signs are feeling dazed, confused, or foggy after a hit to the head or body. This misconception should never lead anyone to dismiss a real head injury.
How long does a concussion typically last?
Most people recover within days to about a month. Some continue to have symptoms for longer, known as persistent post-concussive symptoms or post-concussion syndrome. Recovery time varies with age, symptom severity, prior concussions, and how activity is managed early on.
What are the warning signs that mean you should go to the ER for a concussion?
Call 911 or go to the emergency room for one pupil larger than the other, repeated vomiting, a worsening headache, a seizure, slurred speech, new weakness or numbness, increasing confusion, or trouble waking up. These can signal bleeding or swelling inside the skull and may develop hours after an injury.
Is there a blood test for concussion?
There is an FDA-cleared blood test measuring two proteins, GFAP and UCH-L1, drawn within about a day of injury. It helps doctors decide whether a head CT is needed, but it does not diagnose a concussion, which remains a clinical diagnosis based on symptoms and exam.
What is post-concussion syndrome?
Post-concussion syndrome describes concussion symptoms, such as headache, dizziness, fatigue, or trouble concentrating, that continue for weeks or months longer than usual. It affects a minority of people and is generally treatable by targeting the specific symptom causing the most trouble.
When is it safe to return to sports or exercise after a concussion?
Nobody should return to play the same day as a suspected concussion, even if symptoms clear quickly. After brief relative rest, most people begin light, symptom-guided activity and progress through a stepwise return-to-play protocol, with clearance from a qualified clinician, not a fixed date.
Sources
- Centers for Disease Control and Prevention — Signs and Symptoms of Traumatic Brain Injury — CDC, 2024 — cdc.gov
- MedlinePlus, National Library of Medicine — Concussion — MedlinePlus, 2024 — medlineplus.gov
- Cleveland Clinic — Concussion — Cleveland Clinic Health Library, 2023 — my.clevelandclinic.org
- 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 — British Journal of Sports Medicine, 2023 — doi.org/10.1136/bjsports-2023-106898
- Lagares A, de la Cruz J, Terrisse H, et al. — An automated blood test for glial fibrillary acidic protein (GFAP) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) to predict the absence of intracranial lesions on head CT in adult patients with mild traumatic brain injury: BRAINI, a multicentre observational study in Europe — EBioMedicine, 2024 — doi.org/10.1016/j.ebiom.2024.105477
- Alashram AR, et al. — Effects of aerobic exercise on concussion-related symptoms: a systematic review of randomized controlled trials — Brain Injury, 2025 — doi.org/10.1080/02699052.2025.2476494
Further reading
- Understand another condition that affects memory over time in this guide to Alzheimer’s disease symptoms and stages.
Understand your lab results with BloodSense
Most people recovering from a concussion do not need routine blood work, since the injury is diagnosed by history and examination, not a lab test. The main exception is the emergency evaluation of a new head injury, where the GFAP and UCH-L1 blood test helps decide whether a head CT is necessary. If symptoms linger, a doctor may order general blood tests, such as a thyroid panel, complete blood count, or vitamin levels, to check for other conditions adding to fatigue or brain fog.
Seeing where each value sits against its reference range makes results easier to discuss with your care team, especially when persistent symptoms make it hard to tell what is from the concussion and what has another cause. BloodSense translates a full lab report into plain language, helping you track changes over time instead of reading one line in isolation.
