It has become clear that impact sports like football and boxing can cause long-term brain damage. Now soccer is coming under scrutiny. As evidence mounts that excessively heading a soccer ball can injure a player’s brain, professional players such as Brandi Chastain, a star of the 1999 FIFA Women’s World Cup, are using this year’s tournament to call attention to the health risks facing young players. To learn about the latest science on soccer heading and brain injuries, Scientific American spoke to Robert Cantu, professor of neurosurgery at the Boston University School of Medicine and co-founder of the Sports Legacy Institute. What’s the scientific evidence for whether heading a soccer ball can cause brain damage? Our findings and the findings of other researchers show that heading a soccer ball can contribute to neurodegenerative problems, such as chronic traumatic encephalopathy. Researchers who’ve followed soccer players have seen a close relationship between the amount of heading that a player does and brain abnormalities. There’ve also been studies where researchers compared soccer players to swimmers, and swimmers’ brains look perfectly normal while the soccer players’ brains had abnormalities in their white matter fiber tracts. Nerve cells transmit their messages to other nerve cells by way of their fiber tracts, or axons, and if the brain is violently shaken enough, a person can have disruption of their fiber tracts. What are the effects of these brain abnormalities? Excessive shaking of the brain—excessive subconcussive and concussive trauma—can lead to cognitive symptoms, including memory problems as well as behavior and mood problems such as anxiety and depression. Other symptoms include trouble with sleep, light-headedness and headaches.