Sacramento — WE’VE known since 1964 that cigarette smoking is harmful to your health. We’ve known for more than 40 years that alcohol damages the developing brain of a child. We’ve known since the mid-70s that asbestos causes cancer and other serious diseases. Knowing what we know now, we do not smoke in enclosed public spaces like airplanes; we have passed laws to keep children from smoking or drinking alcohol; and we do not use asbestos as an industrial product.

As we become more intellectually sophisticated and advanced, with greater and broader access to information and knowledge, we have given up old practices in the name of safety and progress. That is, except when it comes to sports.

Over the past two decades it has become clear that repetitive blows to the head in high-impact contact sports like football, ice hockey, mixed martial arts and boxing place athletes at risk of permanent brain damage. There is even a Hollywood movie, “Concussion,” due out this Christmas Day, that dramatizes the story of my discoveries in this area of research. Why, then, do we continue to intentionally expose our children to this risk?

If a child who plays football is subjected to advanced radiological and neurocognitive studies during the season and several months after the season, there can be evidence of brain damage at the cellular level of brain functioning, even if there were no documented concussions or reported symptoms. If that child continues to play over many seasons, these cellular injuries accumulate to cause irreversible brain damage, which we know now by the name Chronic Traumatic Encephalopathy, or C.T.E., a disease that I first diagnosed in 2002.