You can still get a concussion even while wearing a helmet. A concussion is a form of mild traumatic brain injury (mTBI) that results from an impact or a sudden, violent movement of the head or body, causing the brain to move rapidly inside the skull. While helmets are incredibly effective safety devices, they are engineered primarily to mitigate different types of injury than the complex forces that cause a concussion. This distinction explains the limitations of current helmet technology in fully safeguarding against this common injury.
The Difference Between Skull Protection and Concussion Prevention
The fundamental design goal of most helmets is to manage the energy from a direct, straight-on impact to the head. Helmets excel at protecting the skull and preventing catastrophic structural injuries by absorbing and dissipating linear forces. A typical helmet features a hard outer shell and a layer of crushable foam, often expanded polystyrene, designed to deform upon impact. This shell spreads the force over a larger surface area, and the foam prolongs the duration of the impact, effectively reducing the peak acceleration transferred to the head. This mechanism significantly lowers the risk of severe injuries like skull fractures and life-threatening intracranial hemorrhages.
A concussion, however, is an injury to the soft tissue of the brain itself, often occurring without any fracture or external head trauma. The protection offered against skull and focal injuries does not fully translate to protection against the more subtle, diffuse damage associated with a concussion.
Understanding the Mechanism of Concussion
A concussion occurs when the head undergoes a rapid change in velocity, causing the brain to move within the cerebrospinal fluid that surrounds it. This movement subjects the brain tissue to powerful inertial forces, which include linear and rotational acceleration.
Linear acceleration is a straight-line force, such as a direct blow to the front of the head, which causes the brain to slam against the inside of the skull. This force mainly creates pressure gradients within the brain. Rotational acceleration, resulting from an oblique or angled impact, is considered the predominant mechanism for most concussions.
This twisting or shearing force causes the brain to rotate relative to the skull, leading to widespread deformation of the brain tissue. The rapid rotation causes the long, delicate nerve fibers, called axons, to stretch or tear. This stretching, known as diffuse axonal injury, disrupts the brain’s internal communication system and is linked to concussion symptoms.
Why Helmets Cannot Eliminate Concussions
Current helmet technology has a significant limitation in its ability to mitigate the rotational forces that are the primary cause of concussions. While the foam padding is highly effective at managing linear acceleration, it is far less effective at dampening the twisting motion. Because the helmet is essentially mounted to the head, the head and the helmet accelerate and rotate together during an angled impact. This means the rotational forces are still transferred through the skull to the brain floating inside.
Standard helmet testing has historically focused on straight-on impacts, which prioritize the mitigation of linear forces and severe structural injuries.
Although newer designs incorporate technologies like slip-plane layers to allow the outer shell to rotate independently of the inner liner, thereby attempting to redirect some of the rotational energy, no existing helmet can completely neutralize these forces. The brain still moves inside the skull, and that internal movement is what causes the concussive injury.
The Essential Role of Helmets in Injury Mitigation
Despite their inability to prevent every concussion, helmets remain a necessary safety measure in countless activities. Their effectiveness in absorbing linear impact energy is indisputable, significantly reducing the risk of catastrophic head injuries.
Helmets prevent the most devastating outcomes, such as skull fractures and acute subdural hematomas, which are often immediately life-threatening. Studies consistently show that wearing a helmet dramatically decreases the incidence of severe traumatic brain injuries across sports, cycling, and motor vehicle use.
Ongoing research is focused on improving helmet designs to better address rotational acceleration, often through systems that allow a small amount of movement between the head and the helmet upon impact. Until a definitive “concussion-proof” technology is developed, wearing a properly certified and fitted helmet remains a vital step in minimizing the overall risk of head injury.