Concussions are serious traumatic head injuries that occur from both mild and severe blows to the head. Some head injuries may appear to be mild, but recent research is finding that concussions can have serious, long-term effects, especially repeat head injuries or cumulative concussions.

A concussion is typically caused by a severe head trauma during which the brain moves violently within the skull. The brain cells all fire at once, much like a seizure. Some studies show that patients who suffer a concussion appear to have the brain activity of people in a coma.

A concussion may result from a fall in which the head strikes against an object or a moving object strikes the head. A suddenly induced turning movement such as a blow that twists the head (like a punch to the side of the face) is more likely to produce unconsciousness. However, significant jarring in any direction can produce unconsciousness.

An estimated 300,000 sports related traumatic brain injuries (TBIs) occur in the United States each year, ranging from mild to moderate severity, most of which can be classified as concussions. The proportion of these concussions that are repeat injuries is unknown; however, there is an increased risk for subsequent TBI among persons who have had at least one previous TBI . Repeated mild brain injuries occurring over an extended period (i.e., months or years) can result in cumulative neurologic and cognitive deficits, but repeated mild brain injuries occurring within a short period (i.e., hours, days, weeks) can be catastrophic or fatal. The latter phenomenon, termed “second impact syndrome” has been reported more frequently since it was first characterized in 1984.