It is a common experience to feel a sudden rush of moisture to the eyes the moment a sneeze takes over. The explanation for this involuntary reaction lies not in a sudden surge of tears, but in the rapid and intense mechanical forces generated by the body’s protective expulsion reflex. A sneeze is a rapid, involuntary defense mechanism designed to clear the nasal passages of irritants. The watering of the eyes is a direct, temporary consequence of the physical mechanics involved in this explosive bodily event.
The Explosive Sneeze Reflex
A sneeze is a complex, involuntary reflex that begins when sensory nerve endings in the nasal lining detect an irritant, such as dust or pollen. This signal travels along the trigeminal nerve to a specialized area in the brainstem, known as the sneeze-evoking zone, which coordinates the entire process. The reflex involves a rapid, deep inhalation, followed immediately by the forced contraction of numerous muscle groups throughout the chest, throat, and face.
The glottis and soft palate momentarily close to trap air within the lungs and nasal cavity, causing a significant increase in pressure inside the respiratory system. When the airways open, this trapped air is explosively expelled at a high velocity to clear the nasal passages, and the sheer force generated sets the stage for the temporary eye watering that follows.
Temporary Blockage of Tear Drainage
The reason tears spill onto the cheek during a sneeze is due to a momentary disruption of the eye’s drainage system. Tears are produced continuously to lubricate the eye and normally drain away through two tiny openings, called puncta, located in the inner corners of the eyelids. From the puncta, tears travel through small channels and eventually enter the nasolacrimal duct, which empties directly into the nasal cavity.
This drainage system carries tears into the nose, which is why a person may experience a runny nose after crying. During the explosive phase of the sneeze, the powerful contraction of facial muscles temporarily compresses the nasolacrimal duct, creating a momentary blockage that causes tears to back up and overflow the eyelid margin.
Irritants That Exacerbate Sneezing
While the mechanical blockage of the tear duct is the cause of the overflow, the amount of fluid available to spill can be increased by the irritant that triggered the sneeze. Many stimuli that prompt a sneeze, such as pollen, dust mites, or animal dander, are common allergens that cause a condition called allergic rhinitis, or hay fever.
When these allergens contact the eyes and nose, the immune system releases histamine. Histamine causes inflammation and swelling in the mucous membranes, leading to increased tear production and a runny nose. This increased tear volume, combined with the mechanical blockage during the reflex, makes the watery-eye phenomenon especially noticeable during allergy season or when exposed to environmental triggers.