Motorcycle helmets are really good at protecting your head from a skull fracture or face fracture. But if there is a crash which causes the rider to rapidly decelerate the rider can suffer a special type of brain injury called a diffuse axonal brain injury.
A diffuse axonal injury is the shearing (tearing) of the brain’s long connecting nerve fibers (axons) that happens when the brain is injured as it shifts and rotates inside the bony skull. These can be very serious and deadly injuries.
Seventy-five percent of all fatal motorcycle accidents involve head and brain injury, with rotational forces acting on the brain being the primary cause of death. A motorcycle helmet may be unable to protect against this type of injury because the injury happens inside the skull. .