So-called “second impact syndrome” was first described as the phenomenon of sudden death from rapidly progressing brain swelling due to a second concussion sustained soon after a first one. Recently, however, the scientific evidence behind that definition of second impact syndrome has been criticized.
It’s true that in rare cases, a traumatic brain injury can lead to a catastrophic neurological decline — or even death — from rapid brain swelling, especially in children. This phenomenon, however, is not linked to two consecutive concussions. In fact, it can occur from a single, first-time concussion. A true “second impact syndrome” death is the rare exception rather than the rule after a second concussion.
There is, however, an increased risk of a second concussion from an injury sustained soon after a first concussion. This may be due to slower reaction times, dizziness, headache, and other concussion symptoms related to incomplete healing and recovery of the first concussion.
In this sense, then, there is indeed a risk of “second impact,” but that term is often confused with the original meaning of a sudden death from a second impact that is still controversial in the scientific literature.