In addition to taking a detailed concussion history, asking an athlete about the number and severity of post-concussion signs or symptoms and conducting a neurological examination, both during a pre-participation physical evaluation (PPE), it is critically important for your child's treatment of and recovery from a suspected concussion to provide the treating health care professional with as much information as possible about all prior concussions, including severity of impact and duration of symptoms.
Because many athletes, particularly children under the age of 13 - for whom the most recent international consensus of concussion experts  recommends asking a different set of questions than older athletes, including questions directed to their parents  - do not recognize all the concussions they may have suffered in the past, a structured concussion history should therefore "include specific questions as to previous symptoms of concussion and length of recovery, not just the perceived number of concussions." 
While some research suggests that those with prior concussions do not necessarily suffer more neurocognitive impairment following a re-injury, [1,15] other studies have found that athletes who have suffered multiple concussions are at increased risk for subsequent concussion and more likely to develop persistent post-concussion signs or symptoms, including depression, which require careful management and may have life-long health consequences. A 2009 study  of high school soccer players, for example, found that athletes with a reported history of concussions performed significantly worse on tests of memory, visual processing and reaction time using the ImPACT computerized neurocognitive test battery than those who reported no prior concussion
Under the consensus statement issued after the 4th International Conference on Concussion in Sport in Zurich in November 2012  frequency (repeated concussions over time), concussions close together in time, recent concussion or traumatic brain injury, and repeated concussions occurring with progressively less impact force or slower recovery after each successive concussion are considered important "modifying factors" in concussion management which may, in some cases, predict the potential for prolonged or persistent symptoms that may lead to a diagnosis of post-concussion syndrome.
The importance of finding out about concussion history is underscored by studies showing that a significant percentage of athletes, especially in contact sports like football, suffer multiple concussions over the course of their athletic career, many of which, for a variety of reasons, go unreported: [11,12,13]
- Between 11.5% and 13.2% of concussions among high school athletes are recurrent. [3,4]
- College football players with a history of 3 or more previous concussions were 3.4 times more likely to sustain another concussion than those with no concussion history, with an increased likelihood of recurrent concussions increasing with the number of previous concussions; 
- The same study suggested that a multiple concussion history was associated with a slower recovery of neurological function after another concussion. The study also found that, within a given season, there may be increased susceptibility to another concussion in the first 7 to 10 days after the initial concussion;
- 16.8% of high school athletes suffering a concussion had previously suffered a sport-related concussion, either that season or in a previous season;
- More than 20% of concussions in boys' and girls' soccer and basketball were recurrent concussions;
- Once an athlete has suffered an initial concussion, his or her chances of a second one are 3 to 6 times greater than an athlete who has never sustained a concussion;
- A third of high school players in one recent survey reported two or more concussions in a season.
- High school football players with a concussion history were nearly 3 times more likely to sustain another, whereas non-football players were 1.2 times more likely.
- High school athletes who have been concussed are three times more likely to suffer another concussion in the same season.
- High school athletes who suffer 3 or more concussions are at increased risk of experiencing loss of consciousness (8-fold greater risk), [3,6] anterograde amnesia (reduced ability to form new memories after a brain injury) (5.5-fold greater risk), and confusion (5.1-fold greater risk) after a subsequent concussion.
- In one study, healthy high school students with a history of two or more concussions exhibited poorer performance on the ImPACT neurocognitive test than healthy students with a history of one or no concussion;  a more recent study, however, found no such adverse lingering effect on performance on computerized neurocognitive tests.
- After recovering from a concussion, high school students with a history of two or more concussions continue to report significantly more physical, cognitive, and sleep-related concussion symptoms than healthy students with a history of one or no concussion. 
- Children who are seen in a hospital emergency room for a head injury (concussion, skull fracture or intracranial injury) are more than twice as likely to sustain a subsequent head injury of similar type within 6 months as are children seeking care for an injury not related to the head, regardless of their age.
- A history of head injury is an independent risk factor for concussion, with a relative risk between 2.04 and 2.28 in athletes who have sustained a previous concussion. [9,10]
- Recurrent concussions, as compared with initial ones, have been linked to a prolonged time to symptom resolution. 
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2. McCrory P. et al. Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br. J. Sports Med. 2013; 47:250-258.
3. Castile L, Collins CL, McIlvain NM, Comstock RD. The epidemiology of new versus recurrent sports concussions among high school athletes, 2005-2010. Br. J. Sports Med 2012; 46:603-610.
4. Marar M, McIlvain NM, Fields SK, Comstock RD. Epidemiology of concussions among United States high school athletes in 20 sports. Am J Sports Med 2012;40:747-755.
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6. Collins MW, Lovell MR, Iverson GL, Cantu RC, Maroon JC, Field M. Cumulative effects of concussion in high school athletes. Neursurgery. 2002;51(5):1175-1181.
7. Moser RS, Schatz P, Jordan B. Prolonged effects of concussion in high school athletes. Neurosurgery 2005;57:300-306.
8. Schatz P, Moser RS, Covassin T, Karpf R. Early Indicators of Enduring Symptoms in High School Athletes with Multiple Previous Concussions. Neurosurgery 2011: 000 (in process).
9. Emery CA, Kang J, Schneider KJ, Meeuwisse WH. Risk of injury and concussion associated with team performance and penalty minutes in competitive youth ice hockey. Br J Sports Med 2011;45:1289-1293.
10. Schulz MR, Marshall SW, Mueller FO, Yang J, Weaver NL, Kalsbeek WD, et al. Incidence and risk factors for concussion in high school athletes in high school athletes, North Carolina, 1996-1999. Am J Epidemiol 2004;160:937-944.
11. McCrea M, Hammeke T, Olsen G, Leo P, Guskiewicz K. Unreported concussion in high school football players: implication for prevention. Clin J Sport Med 2004;14:13-17.
12. Echlin PS, Tator CH, Cusimano MD, Cantu RC, Taunton JE, Upshur RE, et al. A prospective study of physician-observed concussions during junior ice hockey teams: implications for sports concussion education. Neurosurg Focus 2010;29(5):E4.
13. Echlin PS, Skpelja EN, Worsley R, Dadachanji SB, et al. A prospective study of physician-observed concussion during a varsity university ice hockey season: incidence and neuropsychological changes. Part 2 of 4. Neurosurg Focus 2012;33(6):E2.
15. Brooks BL, McKay CD, Mrazik M, Barlow KM, Meeuwisse WH, Emery CA. Subjective, but not Objective, Lingering Effects of Multiple Past Concussions in Adolescents. J Neurotrauma 2013;30:1469-1475.
Most recently revised and updated October 29, 2013