When rotated from side to side and rocked from back to front, the scalp should move with the helmet. Helmets decrease the severity of injury, the likelihood of death, and the overall cost of medical care. They're designed to cushion and protect riders' heads from the impact of a crash. Just like safety belts in cars, helmets can't provide total protection against head injury or death, but they do reduce the incidence of both. Studies show helmets are about 29 percent effective in preventing motorcyclist deaths.
Helmets are even more effective in preventing brain injuries.