Medicine has not yet figured out how many concussions is too many. The number that leads to permanent deficits in memory, concentration, and other cognitive processes, and/or that increases the risk of dementia [1] and other problems later in life, is likely to be different for each athlete.
Several other factors besides the overall number will help influence a recommendation to an athlete to consider retiring from contact or collision sports, including:
For most athletes, retiring from contact or collision sports has a major impact on their lives.
The decision to retire should be made jointly, after long discussion between the athlete, the athlete's family, other people important to the athlete (e.g. coach) and the team involved in the athlete's care, including the physician, neuropsychologist, nurse practitioner, and other members of the care team, and takes place over a series of visits lasting weeks to months during which the following is explained to the athlete and others:
For those young athletes who do not seek to play professional sports, or who do not have a realistic chance of doing so, most will assume less risk, and will retire from high-risk sports after fewer concussions than prompt an athlete who earns their living by playing professional sports to retire.
Ultimately, athletes make the decisions themselves, and only in very rare cases will a doctor refuse to allow an athlete to return against his or her wishes, and, even then, they are encouraged to seek a second opinion.
Adapted from Kids, Sports, and Concussion by William P. Meehan, III, M.D. (Praeger 2011)
Links:
[1] https://mail.momsteam.com/node/3289
[2] https://mail.momsteam.com/node/149
[3] https://mail.momsteam.com/node/3227
[4] https://mail.momsteam.com/node/3384
[5] https://mail.momsteam.com/node/3385
[6] https://mail.momsteam.com/node/1977
[7] https://mail.momsteam.com/node/1219
[8] https://mail.momsteam.com/health-safety/concussion-evaluation-management-return-to-play-decision-involves-many-factors
[9] https://mail.momsteam.com/health-safety/effects-concussion-suble-yet-prolonged-those-with-multiple-concussion-history
[10] https://mail.momsteam.com/pcss/teens-with-multiple-concussion-history-much-more-likely-report-continuing-symptoms
[11] https://mail.momsteam.com/health-safety/quitting-contact-collision-sport-after-concussion-tough-family-not-just-athlete
[12] https://mail.momsteam.com/repetitive-brain-trauma-and-chronic-traumatic-encephalopathy-CTE-cause-and-effect-relationship-scientifically-premature