Introduction.

“When do concussion symptoms start?” The answer isn’t always straightforward. Some concussion symptoms appear immediately after a head injury, while others may take time to develop. In many cases, symptoms can be delayed for up to 48 hours, though they typically don’t appear beyond 72 hours. Understanding when and why symptoms start is crucial for proper diagnosis and management.

This article will explore:

  • How and when concussion symptoms typically appear
  • Why some symptoms may be delayed
  • When symptoms might not actually be related to a concussion
  • What to do if you suspect a concussion

By understanding these key points, individuals can be better equipped to identify and respond to concussions effectively.

Understanding the Onset of Concussion Symptoms.

Concussion symptoms can vary widely from person to person. According to Giza and Hovda (2014), head trauma triggers a neurometabolic cascade, a complex chain of events that leads to an immediate energy crisis in the brain. This involves a surge of neurotransmitters, an influx of calcium and potassium ions, and temporary reductions in cerebral blood flow—ultimately disrupting normal neural function.

While some symptoms, such as dizziness, confusion, headache, nausea, and sensitivity to light or noise, appear early, others may be delayed, emerging over a 24 to 48 hour period as the brain struggles to meet its energy demands.

What Happens in the Brain During a Concussion:

  • Immediate Phase (Minutes to Hours Post-Injury): The brain undergoes a sudden energy crisis as neurons struggle to function due to ion imbalance and reduced glucose availability. Early symptoms typically include confusion, dizziness, memory difficulties, and headaches.
  • Acute Phase (Hours to Days Post-Injury): The brain attempts to restore balance, but mitochondrial dysfunction impairs energy production. This prolonged energy deficit can result in ongoing symptoms such as brain fog, fatigue, headaches, and difficulty concentrating.

Since symptoms may not appear immediately, recognizing and monitoring for delayed signs is crucial for proper concussion management and recovery.

When Do Symptoms Generally Appear?

Research has shown that while many concussed athletes experience symptoms immediately, a significant percentage develop symptoms hours later or even the next day. 

  • Duhaime et al. (2012) found that among collegiate athletes with acute concussions, 54% reported immediate symptoms, while 25% experienced delayed symptoms. 
  • Similarly, Olson et al. (2020) reported that 83% of pediatric athletes developed symptoms within the first 15 minutes, but 16% experienced delayed onset, emerging between 1 to 12 hours post-injury. 
  • In a pediatric concussion clinic study, 28.1% of young athletes noted that most of their symptoms began more than an hour after the injury (Ellis et al., 2017). 
  • Lastly, Trbovich et al. (2023) examined symptom timing in adolescent athletes, reporting that while 75% experienced immediate symptoms (within 60 seconds of injury), a notable portion still developed symptoms later. 

These findings highlight the importance of monitoring athletes for at least 48–72 hours after a head injury, even if they initially appear fine. They also reinforce the need for early concussion management and immediate removal from play following any suspected head injury to prevent further harm and support proper recovery.

Why Can Symptoms Be Delayed?

While some concussion symptoms appear immediately, others may take hours or even days to develop. Several factors can contribute to this delay, including the body’s initial response to injury and how the brain processes trauma over time. 

  • Adrenaline
      • After a head injury, the body’s natural sympathetic (“fight-or-flight”) response kicks in, releasing adrenaline. This surge in adrenaline can temporarily mask pain and other symptoms, making an individual feel fine in the immediate aftermath. As adrenaline levels drop, symptoms such as headaches, dizziness, and nausea may become more apparent.
  • Cognitive Load and Exertion
      • Many people continue their normal activities after a mild head injury, unaware that they may have a concussion. However, mental and physical exertion—such as reading, working, or exercising—can strain the brain, making symptoms like fatigue, difficulty concentrating, and brain fog more noticeable over time (Brown et al., 2014).
  • Sleep and Rest 
    • Rest is crucial for brain recovery but can also reveal symptoms that weren’t immediately obvious. After a concussion, individuals may wake up feeling groggy, dizzy, or with a worsening headache—signs that their brain is struggling to recover from the injury. Sometimes, people don’t recognize symptoms until they slow down and allow their body to rest.

Understanding these factors can help individuals recognize concussion symptoms, even if they don’t appear immediately, and seek appropriate care when needed.

When Is It Not a Concussion?

While concussion symptoms can be delayed for up to 48-72 hours, symptoms that appear weeks later are much harder to link directly to a concussion. In these cases, other factors may be at play, and assuming a past head injury is the cause can delay proper diagnosis and treatment.

Some possible alternative explanations for late-onset symptoms include:

  • Pre-existing conditions – Issues like migraines, vestibular disorders, or mental health conditions can mimic concussion symptoms.
  • Anxiety and stress – Worrying about a possible concussion can heighten awareness of normal aches, fatigue, or concentration issues, making them feel more significant.
  • Other injuries – Neck injuries (e.g., whiplash) can cause dizziness and headaches, which may be mistaken for lingering concussion symptoms.

If symptoms persist or develop long after the injury, seeing a medical professional for an accurate diagnosis is essential. A concussion specialist can determine whether symptoms are genuinely related to a past head injury or if another condition needs to be addressed.

What to Do If You Suspect a Concussion.

If you or someone you know experiences a head injury, it’s essential to monitor for symptoms both immediately and over the next 48-72 hours. Even if there are no immediate signs of a concussion, symptoms can develop later.

Early removal from play following a suspected head injury is also crucial, as delayed reporting can significantly prolong recovery. Asken et al. (2016) examined the impact of delayed symptom reporting in collegiate athletes and found that 51.5% continued playing despite experiencing concussion symptoms. Those who delayed reporting missed an average of 4.9 more days of activity than athletes who reported symptoms immediately and were 2.2 times more likely to experience a prolonged recovery (eight or more days). 

These findings highlight the risks of “playing through it” and emphasize the importance of immediate symptom recognition, reporting, and removal from play to support a faster and safer recovery.

Seeking help from a concussion expert, like those at Complete Concussion, is crucial for a faster and safer recovery. Early intervention can also help identify red flags and provide clear return-to-learn/work and play strategies, assisting individuals to get back to their daily activities with confidence.

Conclusion.

Concussion symptoms can appear immediately after a head injury, but they may also be delayed for up to 48-72 hours due to the brain’s response to trauma. Understanding this timeline is crucial for recognizing a concussion and ensuring proper care.

Being proactive—monitoring for symptoms, seeking medical advice if they develop, and consulting a specialist if symptoms persist—can make a significant difference in recovery. Early recognition and management help prevent complications and support a safer return to daily activities.

To find a concussion trained clinician near you, visit clinics.completeconcussions.com.

References

Asken, B. M., McCrea, M. A., Clugston, J. R., Snyder, A. R., Houck, Z. M., & Bauer, R. M. (2016). “Playing through it”: Delayed reporting and removal from athletic activity after concussion predicts prolonged recovery. Journal of Athletic Training, 51(4), 329–335. 

Brown, N. J., Mannix, R. C., O’Brien, M. J., Gostine, D., Collins, M. W., & Meehan, W. P. III. (2014). Effect of cognitive activity level on duration of post‐concussion symptoms. Pediatrics, 133(2), e299–e304.

Duhaime, A. C., Beckwith, J. G., Maerlender, A. C., McAllister, T. W., Crisco, J. J., Duma, S. M., et al. (2012). Spectrum of acute clinical characteristics of diagnosed concussions in college athletes wearing instrumented helmets: Clinical article. Journal of Neurosurgery, 117(6), 1092–1099.

Ellis, M. J., Ritchie, L. J., McDonald, P. J., Cordingley, D., Reimer, K., & Nijjar, S., et al. (2017). Multidisciplinary management of pediatric sports-related concussion. Canadian Journal of Neurological Sciences, 44(1), 24–34. 

Giza, C. C., & Hovda, D. A. (2014). The new neurometabolic cascade of concussion. Neurosurgery, 75(4), S24–S33.

McCrory, P., Meeuwisse, W. H., Echemendia, R. J., … (2013). What is the lowest threshold to make a diagnosis of concussion? British Journal of Sports Medicine, 47(5), 268-271.

Morgan, C. D., Zuckerman, S. L., Lee, Y. M., King, L., Beaird, S., Sills, A. K., et al. (2015). Predictors of postconcussion syndrome after sports-related concussion in young athletes: A matched case-control study. Journal of Neurosurgery: Pediatrics, 15(6), 589–598.

Olson, A., Ellis, M. J., Selci, E., & Russell, K. (2020). Delayed symptom onset following pediatric sport-related concussion. Frontiers in Neurology, 11, 963. 

Signoretti, S., Lazzarino, G., Tavazzi, B., & Vagnozzi, R. (2011). The pathophysiology of concussion. PM&R, 3(10), S359–S368.

Trbovich, A. M., Kirschler, A., Preszler, J., Collins, M. W., & Kontos, A. P. (2023). Comparison of clinical outcomes between athletes with immediate and delayed onset of symptoms following sport-related concussion. Clinical Journal of Sport Medicine, 33(1), 26–32.