A sneeze is a rapid, involuntary reflex designed to expel irritants from the nasal cavity. This sudden expulsion launches a mixture of air and mucus particles into the surrounding environment through a complex process of fluid dynamics. Determining how far a sneeze travels requires investigating the physics of the initial velocity and how particles travel through the air.
The Physics of Sneeze Velocity
The popular conception of a sneeze traveling over 100 miles per hour is an exaggeration based on older, inferred estimates. Modern scientific analysis, using high-speed imaging and advanced flow visualization, offers a more accurate picture of the initial expulsion. The initial velocity of the air and mucus mixture is typically much lower than historical estimates, often ranging from 10 to 40 miles per hour. For example, one study found the maximum velocity to be around 10 miles per hour (4.5 meters per second), while other measurements have placed the maximum instantaneous velocity closer to 35 miles per hour (15.9 meters per second).
Regardless of the exact figure, the velocity rapidly decreases due to air resistance almost immediately after leaving the mouth and nose. This initial burst of speed determines the potential range of the expelled particles before the force dissipates. The initial propulsion sets the stage for how far the droplets will travel before they are governed by gravity and air currents.
Ballistic Travel Versus Aerosolized Clouds
The distance a sneeze travels depends on the size of the expelled particles, which fall into two main categories: large ballistic droplets and smaller aerosolized particles. Large, visible droplets (100 micrometers or greater) follow a ballistic trajectory. Because they are heavy, gravity quickly pulls them down, causing them to settle within 3 to 6 feet (1 to 2 meters) of the person who sneezed.
The majority of a sneeze’s payload is carried by an invisible, turbulent gas cloud, known as a multiphase plume. This cloud consists of thousands of smaller, lighter particles, called aerosols, that are less than 5 micrometers in size. The cloud mixes with the surrounding air, extending the range of these tiny particles by keeping them suspended far longer than if they were traveling alone.
Under certain conditions, especially where ventilation is poor, this aerosolized cloud can travel significantly farther than the larger droplets. Research has shown that these smaller particles can be carried in the turbulent plume for distances reaching 20 to 27 feet (6 to 8 meters) before fully dissipating. The actual travel distance is heavily influenced by environmental factors like humidity and air circulation, with some models suggesting aerosol particles can travel over 30 meters.
Practical Mitigation and Lingering Time
The primary action to limit the reach of a sneeze is to disrupt the formation and spread of the turbulent gas cloud. Covering a sneeze, ideally into the crook of the elbow, acts as a physical barrier that immediately reduces the initial momentum. This simple action prevents the cloud from forming a clear, forward trajectory and effectively mitigates the distance the particles are launched.
Even after the initial plume has slowed, the smallest aerosolized particles can remain suspended for a considerable duration known as “lingering time.” These light particles are easily influenced by ambient air movement and can stay airborne for minutes, or even hours, especially in poorly ventilated indoor spaces. The time it takes for particles to fall is directly related to their size. This lingering time means the infectious potential of a sneeze can persist in an environment long after the person has left.