A concussion is a mild traumatic brain injury that occurs when a sudden blow or jolt causes the brain to move rapidly inside the skull. This forceful movement or rotational acceleration disrupts normal brain function, leading to temporary neurological changes. A standard sneeze does not generate the necessary force or rotational movement to cause this type of injury.
The Biomechanics of a Sneeze
The physical forces generated during a sneeze are significant, but they are primarily directed outward and are momentary. The expelled air can reach speeds of up to 112 miles per hour, creating substantial internal pressure in the respiratory system. This pressure, estimated to reach about 7,000 Pascals in the trachea, is an instantaneous, non-rotational force.
The force required to cause a concussion is measured in G-forces, typically ranging from 70 to 120 G’s. In contrast, even a violent, unsuppressed sneeze generates a maximum force on the body of approximately 3.5 G’s. This difference explains why the body’s natural defense mechanisms prevent traumatic brain injury from this reflex.
Protective Measures Against Head Injury
The body possesses several layers of protection that neutralize the minor forces exerted during a sneeze. The brain is suspended within the skull in cerebrospinal fluid (CSF). The CSF acts as a hydraulic cushion, absorbing small impacts and jolts by allowing the brain to float slightly, preventing it from striking the interior of the skull.
The bony structure of the skull provides a rigid casing to shield the brain. The cervical spine and surrounding neck muscles act as the final line of defense. These powerful muscles reflexively contract during a sneeze, stabilizing the head and preventing the rapid rotational movement that is the most common cause of a concussion.
Non-Concussive Injuries Caused by Sneezing
While a concussion is highly unlikely, the sudden, intense pressure from a forceful sneeze can cause other localized, non-neurological injuries. The rapid spike in blood pressure can cause tiny capillaries to burst, resulting in a subconjunctival hemorrhage. This appears as a bright red patch on the white of the eye, but the burst vessel is harmless and resolves within a few days.
A powerful contraction of the chest and back muscles can also result in musculoskeletal injuries. Spontaneous rib fractures have been reported, particularly in individuals with pre-existing conditions like severe osteoporosis or chronic obstructive pulmonary disease. Extremely rare instances of laryngeal fractures or pneumothorax (collapsed lung) have been documented, almost exclusively due to the intense internal pressure created by suppressing a sneeze.
Specific Conditions Required for Concussion Risk
In extremely rare scenarios, a sneeze can act as a trigger for a more serious event in individuals with an underlying medical vulnerability. For those with an unclipped cerebral aneurysm, the brief, sharp spike in blood pressure can cause the weakened vessel wall to rupture. The resulting subarachnoid hemorrhage is a medical emergency, but it is not a concussion.
A violent sneeze involving abrupt head movement can also trigger a vertebral artery dissection. This injury involves a tear in the artery lining in the neck and can lead to a stroke, especially in people with connective tissue disorders or severe cervical instability. Patients who have recently undergone neurosurgery, particularly near the nasal or sinus passages, are advised to avoid forceful sneezing. This prevents disrupting the surgical site and causing a cerebrospinal fluid leak.