When only one eye waters, it almost always points to a problem on that side specifically, whether it’s a drainage issue, a surface irritation, or a structural change in the eyelid. A large clinical study found that the single most common cause of excessive tearing is a blocked tear drainage duct, accounting for about 31% of cases, and this type of blockage is significantly more likely to affect just one eye rather than both. The good news: most causes are treatable once identified.
How Tear Drainage Works
Your eyes constantly produce a thin film of tears to keep the surface moist and clear of debris. Normally, tears drain through two tiny openings (called puncta) in the inner corner of each eye, travel down narrow channels, and empty into a duct that leads to your nose. That’s why your nose runs when you cry. When something disrupts this system on one side, tears pool and spill over the lower lid of that eye only.
Blocked Tear Duct
A blocked nasolacrimal duct is the most frequent explanation for one-sided watering. The duct can narrow or close off from chronic inflammation, past infections, age-related tissue changes, or previous facial injuries. Symptoms include persistent watering, crusty buildup on your eyelashes, and sometimes a gooey discharge. The blockage can also set the stage for infection of the tear sac, a condition called dacryocystitis.
When the tear sac itself gets infected, you’ll typically notice painful swelling near the inner corner of the affected eye, redness, and pus that may ooze from the tear duct opening when you press gently on the area. Acute infections cause obvious pain and swelling. Chronic infections are subtler, producing persistent tearing with occasional discharge that comes and goes over weeks or months.
Functional Epiphora
In about 23% of tearing cases, the drainage anatomy looks perfectly normal on testing, yet tears still overflow. This is called functional epiphora, and it was the second most common diagnosis in a large study of patients with watery eyes. It happens when the tiny pumping mechanism of the eyelid (which squeezes tears into the drainage channels each time you blink) weakens or loses coordination. Functional epiphora tends to be more common in women and, like duct blockages, is significantly more likely to affect one eye than both.
Eyelid Position Changes
Your lower eyelid acts like a gutter that channels tears toward the drainage openings. If the lid turns outward (ectropion) or inward (entropion), that system breaks down on the affected side. Ectropion is the more common culprit for watering. When the lid sags away from the eyeball, tears can’t reach the drainage puncta and instead roll down your cheek. You may also notice redness, a gritty foreign-body sensation, dryness between episodes of watering, and mucus-like discharge. The lower lid may visibly droop or appear turned inside out.
Eyelid malposition accounts for roughly 16% of excessive tearing cases. It often develops gradually with age as the tissues supporting the lid stretch and loosen, which is why it commonly affects one side before the other.
Something in Your Eye
A tiny speck of dust, a loose eyelash, or a small scratch on the surface of the eye triggers an immediate flood of reflex tears on that side only. This type of tearing comes on suddenly and is usually accompanied by sharp discomfort, sensitivity to light, and an urge to squeeze the eye shut. Reflex tearing made up about 18% of cases in clinical studies, though it tends to be more often bilateral than one-sided.
Contact lens wearers are particularly prone to one-sided corneal irritation. A lens that shifts, dries out, or traps a particle underneath can cause intense watering in that eye. If watering comes with blurry vision, significant pain, or a whitish spot on the colored part of your eye, that may signal a corneal ulcer, which needs prompt attention from an eye doctor.
Why the Right Eye Specifically?
There’s nothing anatomically special about the right eye that makes it more vulnerable than the left. When tearing is one-sided, it simply reflects whichever side has the issue: a duct that narrowed first, a lid that loosened more, or the eye that caught a piece of debris. People tend to notice the right side more readily if they’re right-handed (and therefore touch or rub that eye more often), but the underlying causes are the same regardless of which eye is affected.
How Doctors Figure Out the Cause
An eye doctor can usually narrow down the reason in a single visit. The first step is a careful look at your eyelid position and the surface of your eye under magnification. If a blocked duct is suspected, a simple dye test can check whether the drainage system is open: a drop of fluorescent dye is placed in your eye, and after five minutes you blow your nose into a tissue. If the dye appears on the tissue, the duct is working normally. If it doesn’t, the doctor may flush a small amount of saline through the duct opening to pinpoint where the blockage sits. Fluid that flows through easily rules out a structural obstruction and points toward functional tearing instead.
Treatment Depends on the Cause
For surface irritation or a foreign body, removing the irritant and using lubricating drops is often all that’s needed. Reflex tearing from dry eye (which sounds paradoxical but is common) responds well to regular use of artificial tears, which calm the surface enough to stop the overflow cycle.
Eyelid malposition is typically corrected with a minor outpatient procedure that tightens or repositions the lid. Recovery is usually quick, with the watering resolving once the lid sits properly against the eye again.
Blocked tear ducts that don’t resolve on their own can be treated surgically. The most common procedure creates a new drainage pathway between the tear sac and the inside of the nose. Success rates for this surgery range from 70% to 95% depending on where the blockage is located, with blockages lower in the system responding best (up to 100% success in some studies). Most people are evaluated for success at about three months after the procedure, with full recovery typically within that window.
Tear sac infections are treated with antibiotics first, sometimes with warm compresses to help drainage. Once the infection clears, surgery to open the blocked duct is usually recommended to prevent it from coming back.