Editing Concussion (section)

=== Repeat concussion ===
For unknown reasons, having had one concussion significantly increases a person's risk of having another.<ref name="moser" /><ref name="Merck2017" /> Having previously sustained a sports concussion has been found to be a strong factor increasing the likelihood of a concussion in the future. People who have had a concussion seem more susceptible to another one, particularly if the new injury occurs before symptoms from the previous concussion have completely gone away. It is also a negative process if smaller impacts cause the same symptom severity.<ref name="2008 Consensus Statement">{{cite journal | vauthors = McCrory P, Meeuwisse W, Johnston K, Dvorak J, Aubry M, Molloy M, Cantu R | title = Consensus statement on concussion in sport: the 3rd International Conference on Concussion in Sport held in Zurich, November 2008 | journal = Journal of Athletic Training | volume = 44 | issue = 4 | pages = 434–448 | date = Jul–Aug 2009 | pmid = 19593427 | pmc = 2707064 | doi = 10.4085/1062-6050-44.4.434 }}</ref> Repeated concussions may increase a person's risk in later life for dementia, Parkinson's disease, and depression.<ref name="Merck2017" />