How do you guys feel about the number of blows that students (and everybody for that matter) must take to the head after a sparring session?

I used to train at a place where we sparred a lot and after most sessions, I'd leave with a headache.

Surely this is not good for the brain? Has anyone else had similar experiences? Does anyone wear a headguard?

Does anyone know of anyone who has had adverse affects from years of head blows?