A sneeze is a common, involuntary reflex designed to clear irritants from the nasal passages. This sudden expulsion of air often sparks curiosity about its velocity. Understanding the mechanics and speed of a sneeze provides insight into this defense mechanism.
The Speed of a Sneeze
The speed at which air leaves the body during a sneeze has been a topic of varying estimates. Popular accounts suggest speeds up to 100 mph or around 50 mph.
However, recent scientific studies using advanced imaging found different results. A 2013 study reported maximum velocities around 10 mph (4.5 m/s). Another study using particle image velocimetry found velocities of approximately 15.9 m/s, or 35.5 mph. Regardless of the exact figure, the air expelled during a sneeze moves at a considerable speed, demonstrating the force involved.
The Physiological Process
A sneeze is an involuntary reflex initiated when irritants stimulate sensory nerve endings within the nasal lining. These irritants can include dust, pollen, pet dander, or cold air. Upon detection, these nerve endings transmit a signal to a specialized area in the brainstem known as the sneeze center. This center then coordinates a rapid sequence of events involving multiple muscle groups throughout the body.
The process begins with a deep inhalation, filling the lungs with air. The soft palate and tongue elevate, partially closing the passage to the mouth. Pressure builds within the chest and lungs as the diaphragm, intercostal muscles, and abdominal muscles contract forcefully. This muscular contraction creates a sudden blast of air expelled through both the nose and mouth, expelling mucus, foreign particles, and irritants from the nasal cavity.
Why Such Force Matters
The high velocity and force of a sneeze contribute to the dispersion of respiratory droplets. When a person sneezes, thousands of tiny droplets of saliva and mucus are propelled into the air. These droplets can contain viruses, bacteria, and other pathogens. The speed of expulsion allows these droplets to travel considerable distances, potentially several meters from the source.
Larger droplets settle quickly, often within a few feet. Smaller droplets, known as droplet nuclei, can remain suspended in the air for extended periods and travel further, carried by airflow. This widespread dispersion highlights why hygiene practices, such as covering the mouth and nose with a tissue or the elbow when sneezing, are necessary. Such actions help contain the expelled droplets, reducing the spread of infectious particles to other individuals or surfaces.