Guskiewicz et al., 2007 reported in Medicine & Science in Sports & Exercise7 that “retired professional football players with a history of three or more concussions are at a significantly greater risk for suffering from depression later in life compared with those players with no history of concussion.” They believe that changes to the brain, caused by concussion, may eventually lead to the structural changes in the brain seen with major depression.
Athletes who already under-report concussion are also less likely to report depression and anxiety, making it important to recognize the potential mental-health issues these individuals face. Second Impact Syndrome (SIS)
According to (Cantu, et al., 1992) Second Impact Syndrome (SIS) occurs when an athlete has a concussion and experiences another head injury before the symptoms of the first concussion have cleared.8 The second event may seem unimportant, but could still cause damage to the brain.7 Some concussion experts think of SIS as a severe swelling of the brain after an initial brain injury has happened.
Others consider SIS to be controversial but agree that in rare circumstances, any head trauma can lead to brain swelling in vulnerable people.
At first the athlete may appear dazed, even finishing the play, but within minutes or hours they can collapse and become unconscious. With limited or no eye movement, their pupils widen and their breathing fails.7 Although rare, athletes have died or experienced permanent, severe brain damage from SIS. This is a phenomenon mainly seen in children and adolescents.