A sneeze, known scientifically as sternutation, is a powerful physiological event. Its primary function is to protect the respiratory system by forcefully clearing foreign particles and irritants from the sensitive lining of the nasal cavity. When airborne substances like dust, pollen, or pathogens contact the nasal mucosa, a complex reflex is triggered. This rapid expulsion involves a coordinated effort from the body’s musculature, resulting in an explosive burst of air, mucus, and saliva. The sheer force required to expel these irritants suggests an extremely high velocity for the expelled air.
The Measured Speed of a Sneeze
The speed of a sneeze has been a subject of long-standing debate and historical exaggeration. Older estimates, often repeated in popular science, suggested a velocity of up to 100 miles per hour. This figure was not based on direct measurement but rather on inferences about the velocity required to generate tiny droplets. Modern fluid dynamics research, utilizing high-speed cameras and advanced airflow visualization techniques, paints a different picture. These studies show that the velocity is significantly lower and highly variable depending on the individual and the measurement method. Scientifically measured peak velocities for the expelled airflow typically fall into a range between 10 and 40 miles per hour (MPH). For example, one study found a peak velocity of around 10 MPH, while other research indicated a maximum airflow velocity closer to 35.6 MPH.
The Biological Mechanism of a Sneeze
The high velocity is generated by a specific, rapid sequence of muscular actions. A sneeze begins when sensory nerve endings in the nose detect an irritant and send a signal to the sneeze center in the brainstem. The body initiates a deep, rapid inhalation to fill the lungs with a large volume of air. Following the intake, the body suddenly builds immense pressure within the chest cavity, known as intrathoracic pressure. This is achieved by the forceful contraction of the diaphragm, intercostal muscles, and abdominal muscles, while the vocal cords and epiglottis momentarily close. The pressure is suddenly released as the vocal cords relax and the soft palate directs the explosive air primarily through the nasal passage. This rapid expulsion of highly pressurized air generates the high exit velocity.
How Far Sneeze Droplets Travel
The high initial velocity propels respiratory droplets into the environment; a single sneeze can release an estimated 40,000 droplets. The expelled material forms a turbulent gas cloud that encases the liquid particles, significantly affecting their trajectory and travel distance. The largest droplets follow a short, ballistic trajectory, quickly falling due to gravity. However, the majority are smaller, aerosolized particles suspended within the turbulent cloud. This gas cloud delays the deceleration caused by air resistance, allowing the smaller particles to remain airborne longer. While traditional public health measures suggest a 6-foot distance, the particle cloud has been recorded traveling up to 7 to 8 meters (23 to 26 feet).