A head guard is of course essential when sparring- the brain needs to be protected. Velcro fastened at the rear, this guard gives protection to the forhead, cheekbones, and rear of the head. However, the guard leaves the nose and chin exposed: so it won't stop straight jabs to the face, or straight punches used in Karate/Kung Fu etc. An alternative is a full headguard which offers more protection.
Don't forget that a mouth guard is also essential!!!