In most cases, children, adolescents, and adults who suffer a single concussion recover completely and do not experience long-term effects. Post-concussion syndrome (e.g., lingering headaches, dizziness, nausea, difficulty concentrating) occurs in about 10 percent of people who sustain grade 1 or grade 2 concussions.
People who have sustained a concussion are at increased risk for additional head injury. Subsequent concussions may cause long-term neurological disorders, including brain damage that results in memory loss, psychiatric disorders, or reduced cognitive function (e.g., inability to make decisions or plan ahead).
Second impact syndrome is a serious complication that can be deadly. This condition, which can cause severe swelling and bleeding in the brain, occurs when a person suffers a second head injury before concussion symptoms have completely resolved.