Head Health FAQ

What causes concussions and other brain injuries? Brain injuries occur when the head is subjected to biomechanical forces—e.g. a head-on collision. These events expose the brain to damaging accelerative forces, creating pressure gradients and mechanical strain that injure neurons and other brain cells.1

What is a concussion? How are concussions diagnosed? A concussion is a type of brain injury. When diagnosing concussions, medical professionals look for a variety of symptoms. These may include somatic symptoms (e.g. headache), cognitive symptoms (e.g. feeling like in a fog), emotional symptoms, physical signs (e.g. loss of consciousness, amnesia); behavioral changes (e.g. irritability), cognitive impairment (e.g. slowed reaction times), and sleep disturbance (e.g. insomnia). Many frameworks, scorecards, and batteries of tests exist to help medical professionals better standardize the diagnosis of concussions.1

What are the risks of repetitive head impacts or “sub-concussive” impacts? Head impact exposure can be thought of as having several components: frequency, location, magnitude, and cumulative history. Given this complexity, and the variability of each individual’s brain, it is difficult to accurately capture, quantify, and correlate head impact exposure to health outcomes. Consequently, the risks of repetitive head impacts or of “sub-concussive” impacts are unclear. A recent study found an association between sub-concussive impacts and changes to the structure and function of brain cells in young football players, but the implications of these changes remains unknown.2 Some studies have shown an association with functional impairments, while others have failed to find a link. On balance, more studies than not have found negative changes in cognitive function and symptom presentation (e.g. impaired memory and processing speed) associated with repetitive head impacts.3 This is an area of active research that will likely see considerable growth and new developments in the coming years.

What are the long-term effects of concussions and other brain injuries during youth and high-school football? Can they lead to chronic traumatic encephalopathy (CTE) or other neurodegenerative diseases? The developing human brain has properties—related to structure, blood flow, and metabolism—that could increase the risk for and complications of brain injuries.3 Young athletes may also be more susceptible to brain injuries due to larger head to body size ratio and weaker neck muscles.4 While the link between multiple brain injuries during youth and high-school sports and longer term risk of CTE and other neurodegenerative diseases remains unclear,3 this is an area of active research that will likely see considerable growth and new developments in the coming years.

How common are brain injuries in youth and high-school football? A recent, comprehensive analysis found that game/practice concussion rates (per 1000 games/practices) were 2.38/0.59 for youth and 2.01/0.66 for high-school players.5 In the same study, one-season concussion rates (per 1000 athletes) for the 2012 and 2013 seasons ranged between 31.3 to 32.5 for youth football and 55.4 to 99.8 for high-school football.5 At current levels of participation (3 million for youth and 1.1 million for high school)5 this represents roughly 100,000 and 85,000 concussions per year, respectively.

What types of impacts cause concussions and other brain injuries? Brain injury risk is multifactorial, and modulated by factors including, but not limited to: the biomechanical forces of head impact, physiologic structure of the brain and upper torso, history of brain injuries and concussion, and underlying susceptibility to brain injury.3,6 As a result, there is a complicated, and non-linear, relationship between head impacts and brain injury risk.3 Researchers have attempted to understand and quantify this relationship by studying youth and high-school football players with sensor-equipped helmets. Among high-school footballs players, most concussions are caused by head-to-head contact (70.7%).7 Not only do most impacts occur to the front of the head (30%-45%)8,9 but impacts to the front of the helmet are associated with the most concussions (45%), with side impacts being second most frequent (22.3%).7 This may be because impacts to the front and top of the helmet are associated with the greatest linear and rotational accelerations.9,10

How does the force of head impact relate to injury risk? Is there a threshold over which concussions or other injuries are likely to occur? Unfortunately, it is not that simple. As noted above, concussion risk is multifactorial and there is a complicated, and non-linear, relationship between mechanical input and concussion risk. Studies of youth and high-school football players wearing sensor-equipped helmets shed some light on the forces (specifically linear acceleration) experienced during various head impacts. Among high-school students, linear accelerations ranged from 10.0 to 152.3g with a median value of 21.9g and a 95th percentile value of 57.6g.8 Among youth football players, mean linear acceleration during hits in practice was 21.8g, compared to 61.8g in games. Players sustained more hits (2.2) and more high-impact (>80g) hits (2 vs. 11) during games, as compared to practice.11 A study of high school football players found that linear acceleration of >96 g and front/side/top impact were predictive of concussion risk.12 Similar results have been found among NFL players.13 Nonetheless, most experts agree that there is currently inadequate data to define age-related thresholds for linear and rotational acceleration for concussions in youth.3,12,14,15

What can be done to prevent brain injuries and improve youth and high-school football player health? Experts, physicians, and coaches believe that a multi-factor approach is necessary to reduce concussions. Strategies include, but are not limited to: awareness and education, rule changes, removal and return to play regulations, proper hitting and tackling techniques, in- and off-season cervical strengthening and advances in equipment technologies.3 Recent research suggests that rule changes limiting contact in practices may lead to a reduction in concussions.16 Despite these advances, it is important to remember that no intervention, or combination of interventions, will ever eliminate the risk of concussion or other brain injuries in youth and high school football.

How do helmets work? Helmets are designed reduce the likelihood that injury occurs after an impact to the head. Specifically, helmets dissipate and distribute the energy of impact (through hard shells, padding, etc) in order to reduce the accelerative forces the brain experiences. Helmets also protect from penetrative trauma.

Do helmets reduce the risk of concussions and other brain injuries? Football helmets were initially designed to protect from severe and catastrophic injuries such as skull fractures and hemorrhages, and are quite effective in doing so. Less is known about the role of helmets in preventing concussion. This is, in part, because researchers have only recently begun to focus specifically on the efficacy of helmets with respect to concussion reduction. Since helmets are used universally, most research has focused on comparing new and old helmets. For example, researchers compared the performance of traditional helmets (Riddell VSR-4) to newer helmets (Adams Pro Elite, Riddell Revolution, Schutt DNA, and Schutt AVC) in simulated professional-level collisions. Newer helmets were associated with a reduction in impact forces.17,18 The way in which impact force reduction affects concussion risk is less clear. A study of high-school players found that the Riddell Revolution helmet decreased the relative risk of sustaining a concussion by 31% as compared to a variety of older helmets. However, the absolute changes were small—only 2% (7.6% vs. 5.3%).19 Similar results have been reported among NCAA players.18 Complicating this picture, another study of high-school players found no difference in concussion rates across helmet brands, helmet age, or recondition status.6 Reflective of these mixed results, a recent report from the National Resource Council concluded that there is limited evidence that current helmet designs reduce the risk of sports-related concussions.3

Can external helmet devices reduce the risk of concussions and other brain injuries? Research on external helmet devices is even more limited than that of helmet technology. In one study, researchers found that applying layers of foam to the outside of helmets reduced linear impact forces during simulated impacts. Compared to two helmets without foam, two helmets, with two layers of foam each, reduced linear impact forces by 31% and rotational impact forces by 29%.20 Another study examined the efficacy of three external devices (Guardian Cap, UnEqual Technologies’ Concussion Reduction Technology (CRT), and Shockstrips) and found that each reduced linear impact forces by about 11% and rotational impact forces by about 2% as compared to a standard helmet.21 To date, there has been no published research examining the link between external helmet devices and concussions.


  1. McCrory P, Meeuwisse WH, Aubry M, 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(5):250-258.
  2. Bahrami N, Sharma D, Rosenthal S, et al. Subconcussive Head Impact Exposure and White Matter Tract Changes over a Single Season of Youth Football. Radiology.0(0):160564.
  3. National Research Council (U.S.). Committee on Sports-Related Concussions in Youth Board on Children Youth and Families, Graham R, Rivara FP, Ford MA, Spicer CM, Institute of Medicine (U.S.). Sports-related concussions in youth : improving the science, changing the culture. Washington, D.C.: The National Academies Press; 2014.
  4. Pfister T, Pfister K, Hagel B, Ghali WA, Ronksley PE. The incidence of concussion in youth sports: a systematic review and meta-analysis. Br J Sports Med. 2015.
  5. Dompier TP, Kerr ZY, Marshall SW, et al. Incidence of Concussion During Practice and Games in Youth, High School, and Collegiate American Football Players. JAMA Pediatr. 2015;169(7):659-665.
  6. McGuine TA, Hetzel S, McCrea M, Brooks MA. Protective equipment and player characteristics associated with the incidence of sport-related concussion in high school football players: a multifactorial prospective study. Am J Sports Med. 2014;42(10):2470-2478.
  7. Kerr ZY, Collins CL, Mihalik JP, Marshall SW, Guskiewicz KM, Comstock RD. Impact locations and concussion outcomes in high school football player-to-player collisions. Pediatrics. 2014;134(3):489-496.
  8. Urban JE, Davenport EM, Golman AJ, et al. Head impact exposure in youth football: high school ages 14 to 18 years and cumulative impact analysis. Ann Biomed Eng. 2013;41(12):2474-2487.
  9. Daniel RW, Rowson S, Duma SM. Head impact exposure in youth football. Ann Biomed Eng. 2012;40(4):976-981.
  10. Broglio SP, Sosnoff JJ, Shin S, He X, Alcaraz C, Zimmerman J. Head impacts during high school football: a biomechanical assessment. J Athl Train. 2009;44(4):342-349.
  11. Wong RH, Wong AK, Bailes JE. Frequency, magnitude, and distribution of head impacts in Pop Warner football: the cumulative burden. Clin Neurol Neurosurg. 2014;118:1-4.
  12. Broglio SP, Schnebel B, Sosnoff JJ, et al. Biomechanical properties of concussions in high school football. Med Sci Sports Exerc. 2010;42(11):2064-2071.
  13. Zhang L, Yang KH, King AI. A proposed injury threshold for mild traumatic brain injury. J Biomech Eng. 2004;126(2):226-236.
  14. Guskiewicz KM, Mihalik JP, Shankar V, et al. Measurement of head impacts in collegiate football players: relationship between head impact biomechanics and acute clinical outcome after concussion. Neurosurgery. 2007;61(6):1244-1252; discussion 1252-1243.
  15. McCaffrey MA, Mihalik JP, Crowell DH, Shields EW, Guskiewicz KM. Measurement of head impacts in collegiate football players: clinical measures of concussion after high- and low-magnitude impacts. Neurosurgery. 2007;61(6):1236-1243; discussion 1243.
  16. Kerr ZY, Yeargin SW, Valovich McLeod TC, Mensch J, Hayden R, Dompier TP. Comprehensive Coach Education Reduces Head Impact Exposure in American Youth Football. Orthop J Sports Med. 2015;3(10):2325967115610545.
  17. Viano DC, Pellman EJ, Withnall C, Shewchenko N. Concussion in professional football: performance of newer helmets in reconstructed game impacts--Part 13. Neurosurgery. 2006;59(3):591-606; discussion 591-606.
  18. Rowson S, Duma SM, Greenwald RM, et al. Can helmet design reduce the risk of concussion in football? J Neurosurg. 2014;120(4):919-922.
  19. Collins M, Lovell MR, Iverson GL, Ide T, Maroon J. Examining concussion rates and return to play in high school football players wearing newer helmet technology: a three-year prospective cohort study. Neurosurgery. 2006;58(2):275-286; discussion 275-286.
  20. Nakatsuka AS, Yamamoto LG. External foam layers to football helmets reduce head impact severity. Hawaii J Med Public Health. 2014;73(8):256-261.
  21. LLoyd J, Conidi F. Do Football Helmet Add­Ons Reduce Concussion Risk? American Academy of Neurology Annual Meeting; 2015; Poster Session VII: Neuro Trauma, Critical Care, and Sports Neurology.