The experience of having eyes that water excessively while sick, known as epiphora, is a frequent symptom of respiratory illnesses. This overflow of tears is usually a protective reflex, signaling that the body is actively responding to an irritant or an infection. This symptom results from a complex interplay between the body’s immune defenses, specialized anatomical structures, and the actions of various pathogens. Watery eyes are a consequence of the body’s attempt to restore balance and expel invaders.
Systemic Response: Histamine and Inflammation
The primary chemical reason for increased tearing during an illness is the systemic immune reaction, involving the release of inflammatory mediators. When a virus or bacteria is detected, the immune system releases a compound called histamine. This substance is stored in mast cells and is deployed to increase the permeability of small blood vessels throughout the body.
The release of histamine causes vasodilation, or the widening of blood vessels, in mucous membranes. This allows immune cells and fluid to reach the site of infection, contributing to congestion and swelling in the head and face. The tissues surrounding the lacrimal glands also experience this inflammatory response.
The resulting localized irritation and swelling stimulate the lacrimal glands to increase tear production, leading to an overflow. This tear hypersecretion is a generalized defense mechanism, triggered by the inflammatory state. Watery eyes are often a side effect of the body’s systemic response, even if the pathogen has not directly infected the eye itself.
The Physical Backup: Nasal Congestion and Tear Drainage
Beyond the body’s chemical response, watery eyes are frequently explained by a temporary mechanical failure in the tear drainage system. Tears are constantly produced to lubricate the eye, then collected and drained through the nasolacrimal duct system. This duct channels tears from the eye’s surface, through tiny openings called puncta, and down into the nasal cavity.
When a person is sick, the lining of the nasal passages and sinuses becomes inflamed and swollen. This inflammation, combined with increased mucus, can physically block the opening of the nasolacrimal duct where it enters the nose. The blockage prevents the normal flow of tears, causing them to back up and spill over the lower eyelid onto the cheek. The congestion that causes a stuffy nose is often the same swelling that prevents tears from draining properly.
Direct Pathogen Contact: When Sickness Attacks the Eye
In some instances, watery eyes are caused by the direct presence of a pathogen on the eye’s surface, rather than just a systemic side effect. Certain viruses, such as adenoviruses, can travel from the respiratory system to the eye and cause viral conjunctivitis. This direct infection leads to inflammation of the conjunctiva, the thin layer covering the white part of the eye and the inner eyelid.
The irritation from this localized infection triggers a strong protective reflex to flush the eye’s surface. The eyes respond by generating a large volume of watery discharge, aiming to wash away the infectious particles. Viral conjunctivitis is highly contagious and typically presents with watery discharge, redness, and a burning sensation.
It is important to distinguish this from bacterial conjunctivitis, which tends to produce a thicker, often yellow-green, sticky discharge. Regardless of whether the cause is viral or bacterial, the watery discharge is the body’s immediate, localized defense response to the invasion of the eye tissue.