When a cold or the flu takes hold, many people notice their eyes begin to water excessively. This condition, medically known as epiphora, is the overflow of tears onto the face. Understanding this surplus of moisture involves looking closely at the mechanics of tear drainage and the body’s immune response to a pathogen. This phenomenon is often a temporary result of the internal swelling that accompanies viral sickness.
How the Tear System Works
Under normal circumstances, the eye is constantly covered by a thin film of tears that lubricates, nourishes, and protects the delicate surface. This tear film is a complex, three-layered structure. It includes a mucus layer for adherence, a thick watery layer containing antibacterial proteins, and an oily outer layer secreted by the meibomian glands to prevent evaporation.
Tears are continuously produced by the lacrimal glands, situated above the outer corner of each eye, and spread across the surface with every blink. The eye has a dedicated drainage system to prevent overflow. This system starts with tiny openings called puncta in the inner corners of the eyelids. Tears flow through the puncta into the lacrimal sac, which empties into the nasolacrimal duct and directs the fluid into the nasal cavity.
The Mechanical Cause: Nasal and Sinus Congestion
The most common reason for watery eyes during a cold is a physical blockage within the tear drainage system. The nasolacrimal duct travels from the inner corner of the eye down into the nose. When a person has a viral infection, the lining of the nasal passages and sinuses becomes inflamed and swollen as part of the immune response.
Because the duct is closely integrated with the nasal cavity, the swollen nasal tissue exerts pressure on the duct or causes its internal opening to narrow significantly. This temporary narrowing prevents tears from draining efficiently into the nose. Since the eye continues to produce maintenance tears, the fluid backs up in the lacrimal sac and spills over the lower eyelid. The drainage system is temporarily compromised by the surrounding congestion, even if tears are produced at a normal rate.
Tears as an Immune Response
Beyond the physical obstruction, the immune system can directly contribute to tear hypersecretion. When a virus or bacteria invades the respiratory tract, the immune system releases inflammatory mediators like histamines and cytokines. These substances recruit immune cells and manage inflammation, but they can also stimulate the lacrimal glands to increase tear production.
This reflex tearing is a protective mechanism, similar to the response triggered by a physical irritant. The rush of tears serves to flush pathogens from the ocular surface and bathes the eye in antimicrobial proteins like secretory immunoglobulin A. This increased production, combined with decreased drainage capacity, exacerbates the watery eye symptom.
Signs That Watery Eyes Are Serious
While watery eyes are typically a temporary side effect of a cold or flu, certain signs indicate a more serious underlying issue requiring medical attention. If the excessive tearing is accompanied by a thick, pus-like discharge, especially yellow or green, it may signal a bacterial infection, such as conjunctivitis. Significant pain in the eye or around the orbit is also a warning sign.
Changes in vision, such as sudden blurriness or a marked increase in sensitivity to light (photophobia), warrant immediate evaluation. Watery eyes that persist for more than 7 to 10 days after all other cold or flu symptoms have resolved could suggest a chronic obstruction or a different underlying condition. If only one eye is watering excessively, it is more likely to be a localized problem, such as an infection or a foreign body, rather than systemic illness.