What is a concussion, and what should you do about one?

A concussion is a mild traumatic brain injury caused by a direct blow to the head or by forces transmitted to the head, including whiplash from a body impact. The brain moves within the skull, producing a temporary disturbance in function through metabolic and electrical changes rather than structural damage visible on standard imaging, which is why a CT scan is usually normal and is ordered to rule out bleeding rather than to diagnose the concussion. Loss of consciousness occurs in a minority of cases and is not required for diagnosis, which is the most common misunderstanding.

Symptoms fall into four categories and can appear immediately or hours later: physical, including headache, nausea, dizziness, light and noise sensitivity; cognitive, including confusion, difficulty concentrating, memory problems, and feeling foggy; emotional, including irritability and sadness; and sleep disturbance in either direction. Danger signs requiring emergency evaluation are a headache that worsens, repeated vomiting, seizures, unequal pupils, slurred speech, increasing confusion, weakness or numbness, or inability to wake.

Management guidance has shifted. Prolonged complete rest in a dark room is no longer recommended, and current guidance favors a brief initial rest period of about 24 to 48 hours followed by gradual reintroduction of light activity below the symptom threshold, with a stepwise return-to-learn and return-to-play progression supervised by a clinician. The critical rule is not returning to contact activity while symptomatic, because a second impact before recovery can cause severe and occasionally fatal swelling, and repeated concussions are associated with prolonged recovery. Most people recover within weeks, though a minority experience persistent symptoms requiring targeted treatment, and the long-term relationship between repeated head impacts and chronic traumatic encephalopathy remains an active research area.