A new study has revealed a startling link between American football and a degenerative brain disease called CTE.
111 deceased NFL players' brains went under the microscope for the study...and all but one showed signs of the condition.
But as Giles Gibson reports, there's now a growing body of research that shows female athletes could be even more at risk than men:
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With a World Cup and two Olympic medals under her belt, Briana Scurry had the football world at her feet.
But a blow to the head while playing for her club the Washington Freedom in 2010 changed all that.
Scurry immediately knew something was wrong when she saw her team's trainer:
SOT Briana Scurry
"She comes out to meet me and she has her hands out. She's like, "are you OK?" And she looked me dead in the eye and I said, "No, I'm not." And I haven't played since."
For the next three and a half years, Scurry suffered headaches, depression and...eventually thoughts of suicide.
The American Academy of Neurology says female athletes are 50 percent more likely than their male counterparts to have a sports-related concussion.
Right now scientists can't explain why that is, but they're calling for more research into gender differences when it comes to concussions.
As for Scurry, she was able to rebuild her life when a doctor finally diagnosed her with spinal nerve damage.
But while sports medicine experts say data on women's head injuries are still hard to come by, gender-specific treatment options could be on the horizon.
Dr Miho Tanaka runs the Women's Sports Medicine Programme at Johns Hopkins hospital in Baltimore:
SOT Dr Tanaka
"I think having individualised care is really important, whether it's about gender or whether it's about sport or age, and that is the way medicine is headed, so I do anticipate some sort of movement in that direction."
But Dr Tanaka warns gender-specific treatments are at least 5 or 10 years away.
In the meantime, Scurry hopes football's world governing body, FIFA, will change the rules around substitutions and team doctors to better protect players.
FIFA introduced new concussion protocols in 2014, including allowing referees to stop games for three minutes for player assessments.
For Scurry, football helped her dreams come true, but she now wants to make sure the game she loves does everything it can to protect the next generation of players.
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