A sneeze is a sudden, involuntary expulsion of air from the lungs through the nose and mouth. This common reflex occurs when the body activates a response to clear the nasal passages of foreign substances, often due to respiratory infections like a cold or the flu, or allergies. Understanding the mechanisms behind sneezing helps clarify whether the reflex is beneficial for the individual or detrimental to public health.
The Reflexive Function of Sneezing
The body triggers a sneeze as a defense mechanism designed to forcefully clear the nasal cavity and upper respiratory tract of irritants. This process begins when the mucous membranes lining the nose detect foreign particles, excess mucus, or pathogens. The sensory signal travels to the brainstem, which coordinates a complex response involving the chest, abdominal, and facial muscles.
This coordinated effort leads to a rapid and powerful expulsion of air from the lungs. The velocity of the expelled air can reach up to 100 miles per hour, generating high pressure within the respiratory system. This substantial internal force creates the turbulent airflow necessary to sweep contaminants out of the nasal passages.
How Sneezing Spreads Pathogens
While sneezing helps the sick individual, the tremendous force of the expulsion makes it a highly effective mechanism for spreading respiratory illness to others. A single sneeze can release tens of thousands of fluid particles containing mucus, saliva, and viral or bacterial pathogens.
The expelled fluid exists as larger respiratory droplets and smaller aerosols. Droplets (greater than 5 to 10 micrometers) fall quickly due to gravity, typically landing on surfaces within a few feet. Aerosols (less than 5 µm) are light enough to remain suspended in the air for extended periods.
These aerosolized particles can be carried by air currents over much longer distances, contributing to the transmission of viruses like the common cold and flu.
When to Worry and How to Manage Sneezing
The most effective way to manage sneezing while sick is by practicing proper respiratory hygiene, which minimizes the spread of pathogens. The recommended practice is to cover the mouth and nose completely with a tissue when sneezing, then immediately dispose of the used tissue. If a tissue is not available, sneeze into the upper sleeve or the crook of the elbow, rather than the bare hand.
Immediately following a sneeze, washing hands with soap and water for at least 20 seconds prevents indirect transmission. Hands are a common vehicle for transferring germs to shared objects and other people.
When to Seek Medical Attention
Sneezing accompanying a common cold or allergies is generally not a cause for concern. However, consult a healthcare provider if the sneezing is persistent and lasts longer than 10 days, or if it is accompanied by other specific symptoms. Warning signs include a persistent high fever, thick, discolored yellow or green nasal discharge, or severe facial pain or pressure. Difficulty breathing or chest pain also necessitate a medical evaluation, as they may indicate a more serious underlying infection.