Sneezing is a common, involuntary reflex involving the rapid expulsion of air and particles from the respiratory system. It is a sophisticated biological process that protects the body from inhaled irritants and foreign substances.
The Velocity of a Sneeze
A sneeze can generate high speeds. While older estimates suggested velocities around 100 miles per hour (160 km/h), more recent research indicates a range of speeds. Some studies suggest the air from a sneeze can travel between 10 to 30 mph (16 to 50 km/h), with other measurements indicating maximum airflow velocities of about 35 mph. One study recorded expelled particles traveling at up to 103.6 mph (167 km/h). These variations can depend on individual factors such as lung capacity, body size, and the force exerted.
The Sneeze Reflex: Triggers and Purpose
The sneeze reflex is initiated by sensory nerve endings in the nasal cavity and throat. Common irritants include allergens like pollen, dust, mold, and pet dander. Viral infections, such as the common cold or flu, and environmental irritants like smoke, strong odors, or sudden temperature changes also induce sneezing. Some individuals experience a “photic sneeze reflex,” where exposure to bright light, especially sunlight, can trigger a sneeze. This inherited trait affects a portion of the population.
Once an irritant is detected, nerve cells in the nose send a signal to the brain’s sneeze center in the brainstem. This signal travels through the trigeminal nerve network, which plays a central role in initiating the reflex. The brain then orchestrates a rapid response to expel the foreign substance. The purpose of sneezing is to clear the nasal passages and respiratory tract of irritants, pathogens, and foreign particles, acting as a protective mechanism.
The Physiology of a Sneeze
The act of sneezing involves a precise sequence of physiological events. It begins with a deep inhalation, where the diaphragm and intercostal muscles contract to draw a significant volume of air into the lungs. Pressure then rapidly builds within the respiratory system as the soft palate and uvula depress, partially closing the passage to the mouth, and the vocal cords briefly close. Simultaneously, muscles in the chest, abdomen, and throat contract forcefully.
This coordinated muscle contraction generates significant pressure in the lungs. The vocal cords then suddenly open, releasing the pressurized air in a powerful burst through both the nose and mouth. This expulsion is an involuntary, spasmodic action that clears the nasal cavity. The entire process, from initial irritation to expulsion, typically occurs within a few seconds.
The Reach and Impact of Sneeze Expulsions
During a sneeze, a mixture of mucus, saliva, and water droplets is expelled. These expulsions also contain microbes, including bacteria and viruses. Larger respiratory droplets can travel up to 6 feet. However, studies using high-speed imaging have shown that smaller droplets and a turbulent, buoyant cloud of air can carry particles much farther.
Research indicates that sneeze expulsions can travel up to 7 to 8 meters (23 to 26 feet). Smaller droplets, less than 50 micrometers in diameter, can remain airborne for extended periods and travel greater distances, potentially reaching ventilation systems in buildings. This extensive reach underscores the importance of hygiene practices to minimize infectious agent transmission.