We have all experienced the sensation of a runny nose immediately following a burst of tears, whether from laughter, sadness, or a sudden gust of cold air. This reaction suggests a direct link between the eyes and the nasal cavity, which is correct. The connection is a normal part of human anatomy. The reason your nose runs when your eyes water is a combination of simple fluid dynamics and a protective nervous system reflex.
The Plumbing System: Connecting Eye to Nose
The process begins with the lacrimal glands, located above the outer corner of each eye, which constantly produce tears for lubrication and cleaning. After washing over the eye’s surface, tears are collected at the inner corner near the nose. This collection occurs through two tiny openings called the puncta, which act like small drains.
These puncta lead into small canals, known as canaliculi, which merge into the lacrimal sac. The fluid then flows directly into the nasolacrimal duct, commonly referred to as the tear duct. This duct runs downward through a bony canal and empties into the inferior meatus, the lowest passage inside the nasal cavity. Excess tear fluid physically drains from the eye area, down this duct, and directly into the nose, where it mixes with existing nasal mucus.
Why We Produce Excessive Tears
The tear drainage system handles the constant, low-level flow of basal tears used for lubrication and protection. When the eye is overwhelmed, however, tear production increases dramatically, exceeding the duct’s capacity. This overflow leads to tears streaming down the cheek or draining rapidly into the nose.
Excessive tear production is mainly due to two other types of tears: reflex and emotional.
Reflex Tears
Reflex tears are produced in large volumes to wash away irritants, such as dust, smoke, or onion fumes. These tears often contain antibodies, underscoring their protective role.
Emotional Tears
Emotional tears, triggered by strong feelings like sadness or joy, also overwhelm the system, prompting a significant release of fluid from the lacrimal glands.
The volume of these tears surpasses the capacity of the puncta and the nasolacrimal duct to drain them efficiently. When the duct’s capacity is exceeded, the tears flow into the nasal cavity, causing a runny nose. The tears mix with normal nasal secretions, increasing the overall volume of fluid.
The Dual Reaction: Simultaneous Irritation
In some situations, the runny nose is not solely caused by tear overflow, but by a simultaneous reaction triggered by a shared sensory pathway. This dual response is often seen with physical irritants, such as cold air or chemical compounds released by foods like hot peppers. These irritants activate the trigeminal nerve, the primary nerve responsible for sensation in the face.
When the trigeminal nerve endings in the eyes and nasal passages are stimulated, a reflex is initiated. This reflex simultaneously signals the lacrimal glands to produce tears and the nasal lining to increase mucus secretion (rhinorrhea). The increased nasal fluid is a defense mechanism intended to trap and flush out the irritant, while the reflex tearing protects the eyes. Both systems act synchronously to defend the body.