Brain Injury: What is Second Impact Syndrome?

What is Second Impact Syndrome?

Second impact syndrome (SIS), sometimes referred to as recurrent traumatic brain injury, is a brain injury that occurs when a repeat injury is sustained before a previous brain injury has healed. SIS is often fatal. It occurs in teenagers and young adults, typically high school and college athletes. Those who survive usually suffer serious and permanent disabilities.

How it Happens

SIS occurs when a second brain injury is sustained before the initial injury has healed. During SIS, blood rushes to the brain. This causes swelling, pressure on the brain, and herniation of the brain. The second injury does not have to be severe, and may even go unnoticed at first. Victims may seem fine for up to a minute after the second impact, and then suddenly collapse. Brain stem failure and death can occur within a few minutes.


The impact which causes SIS may be very minor and may go unnoticed. A blow to the head is not required. It can be cause by a body blow. The victim may appear stunned, but still able to walk at first. Within a minute or so, a person with SIS will suddenly collapse and display symptoms that resemble a seizure with rapid pupil dilation, loss of eye movement, and rapid breathing. Within minutes of onset, the victim may stop breathing, slip into a coma, or die.


SIS is rare and is only known to occur in children and adolescents, but it is suspected that it may be possible in adults. SIS typically occurs in athletes who return to play too soon after suffering a concussion. SIS is prevented by avoiding a second brain injury, even a minor one, until there are no longer symptoms from the previous injury.

The most effective prevention for SIS is for athletes to stay out of the game and out of practice until all concussion symptoms have resolved.


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