The phenomenon of tears appearing during a yawn is a common experience that often leads people to wonder if they are crying from exhaustion. This involuntary reaction is not an emotional response but rather a mechanical one, demonstrating a direct physical connection between the muscles of the face and the eye’s plumbing system. The watery eyes that accompany a deep yawn are a normal physiological overflow caused by a temporary disruption in the delicate process of tear drainage. Understanding this process requires examining how tears are normally removed from the eye and how the mechanics of a yawn interfere with that system.
The Eye’s Tear Drainage System
The surface of the eye is continuously lubricated by a thin film of tears that must be constantly refreshed and drained away. The tear drainage system, known as the lacrimal apparatus, begins with four tiny openings called lacrimal puncta, located on the inner corner of the upper and lower eyelids. These puncta act as the entry points for excess tears and are normally sufficient to handle the basal tear production needed to keep the eye moist.
Once tears enter the puncta, they travel into small tubes called canaliculi, which direct the fluid toward a small reservoir known as the lacrimal sac. This sac sits nestled in a bone cavity near the nose, where it collects the tears before they move into the final drainage tube. The lacrimal sac then narrows into the nasolacrimal duct, which is the main passageway that empties the tear fluid into the nasal cavity.
The entire drainage process is aided by a mechanism known as the lacrimal pump, which is activated every time a person blinks. Contraction of the orbicularis oculi muscle, the muscle that encircles the eye, compresses the lacrimal sac during a blink. This compression creates negative pressure that pulls tears into the system, ensuring the tear film on the eye’s surface is consistently cleared.
The Physical Action of Yawning
Yawning is a complex, involuntary reflex that involves a coordinated sequence of muscular actions across the chest, throat, and face. The process begins with a deep, prolonged inhalation, where the diaphragm and rib muscles contract to bring a large volume of air into the lungs. This is immediately followed by a wide opening of the jaw and a powerful, generalized stretch of the muscles in the throat and face.
The muscular tension from this deep, wide stretch is significant, causing a noticeable grimace and often leading to the eyes closing tightly. This powerful stretching can also temporarily influence internal pressure dynamics within the head and nasal cavity. The coordinated contraction of these muscles is the physical force that sets the stage for the tear overflow.
How Yawning Triggers Tear Overflow
The deep, forceful movements of a yawn directly interfere with the normal function of the tear drainage system, resulting in the excess fluid spilling onto the cheeks. The primary cause is the powerful contraction of the facial muscles, particularly the orbicularis oculi muscle that surrounds the eye. When this muscle contracts intensely during the peak of the yawn, it squeezes and compresses the structures that make up the tear drainage pathway.
Specifically, the wide opening of the jaw and the accompanying facial muscle tension physically compress the lacrimal sac and the initial segments of the nasolacrimal duct. This compression momentarily blocks or severely restricts the flow of tears down the duct into the nose. Since tears are constantly being produced to maintain eye moisture, the normal volume of fluid has nowhere to go once the drainage route is obstructed.
Furthermore, the mechanical stress of the yawn can sometimes put pressure on the lacrimal glands, which are located beneath the outer part of the upper eyelid. This physical “squeezing” may cause the glands to release a small, additional burst of stored tears, which adds to the fluid volume already waiting to drain.
Because the drainage system is briefly overwhelmed by either the blockage or the slight increase in tear production, the fluid backs up at the inner corner of the eye. Once the volume exceeds the capacity of the eye’s surface, the tears overcome the lower eyelid margin and overflow onto the cheek, which is the exact moment the yawn-induced “crying” is observed. The drainage system typically reopens immediately after the facial muscles relax, allowing the remaining excess fluid to clear.