The last 10 years have seen a major explosion in awareness about the hazards of brain injuries. Most of what we know has come from significantly increased research into the kind of damage that can be done when athletes participate in contact sports like football.
What medical experts have concluded is that repeated tough raps to the head increase the risk of significant mental and physical health issues long term. But more than that, they've discovered that even a single hard hit can cause a concussion. And as one doctor's contribution to The Huffington Post notes, every concussion causes damage.