Constant tearing in one eye usually comes down to one of two problems: something is irritating the eye and triggering extra tear production, or the tiny drainage system that normally carries tears away is partially or fully blocked. Both can affect just one side, which is why your left eye might water while your right eye feels perfectly fine. Figuring out which category you fall into is the key to stopping it.
How Tears Normally Drain
Your eyes constantly produce a thin film of tears to keep the surface moist and protected. With each blink, your eyelids act like a pump, pushing used tears toward two tiny openings (called puncta) in the inner corners of your upper and lower lids. From there, tears flow through narrow channels into a small sac near the bridge of your nose, then down through a duct into your nasal cavity. That’s why your nose runs when you cry.
A problem at any point along this path, from the eyelid’s pumping action to the final drainage into the nose, can cause tears to pool and spill over onto your cheek. And because the plumbing on each side is completely independent, a blockage or malfunction on the left doesn’t affect the right at all.
A Blocked Tear Duct Is the Most Common Culprit
In adults, the nasolacrimal duct (the channel running from the inner corner of your eye down to your nose) can gradually narrow and block over time. This is called nasolacrimal duct obstruction, and it’s the single most frequent reason for persistent one-sided tearing. The blockage may develop from chronic low-grade inflammation, previous sinus infections, or simply age-related narrowing of the duct walls. Sometimes hardened deposits called tear stones form inside the duct and physically plug it.
The hallmark symptoms are a watery eye that never seems to settle down, crusty buildup along the lashes (especially in the morning), and occasionally a sticky or mucus-like discharge. If the backed-up fluid becomes infected, you may notice redness, swelling, and tenderness near the inner corner of the eye, right beside the bridge of the nose. That infection, called dacryocystitis, can sometimes produce a visible lump that oozes pus-like material when pressed. Acute infections cause real pain; chronic ones tend to be more of a painless swelling with ongoing watery or goopy discharge.
Dry Eye Can Paradoxically Cause Watering
This one surprises most people. If the baseline tear film on your eye’s surface is unstable or too thin, the exposed corneal nerves sense irritation and trigger a flood of emergency “reflex” tears. These reflex tears come in a sudden wave, but they’re watery and lack the oily, mucus-rich layers that make a healthy tear film stick to the eye. So they overflow, your eye waters, and the underlying dryness remains, which triggers another wave. It’s a frustrating cycle.
Dry eye can easily be worse in one eye than the other. Research published in the journal Cornea found that people who sleep on their side tend to have worse dry eye disease on the side they press into the pillow. The mechanical pressure against the eyelid clogs the oil glands along the lid margin, leading to chronic inflammation and a less stable tear film on that side. If you sleep on your left side, your left eye may bear the brunt. People who sleep on their back had fewer problems overall.
Eyelid Problems That Disrupt the Tear Pump
Your eyelids need to close tightly and sit flush against the eyeball for tears to drain properly. Two common conditions interfere with this. In ectropion, the lower lid sags or turns outward, pulling the drainage opening away from the eye’s surface so tears have nowhere to go. In entropion, the lid rolls inward, pushing lashes against the eye and causing irritation that triggers excess tearing. Both conditions are more common with age as the tissues supporting the eyelid loosen.
Nerve problems can also play a role. The facial nerve controls the muscles that blink and squeeze tears toward the drainage openings. If that nerve is weakened on one side (from Bell’s palsy, for instance), the pump mechanism on that side stops working efficiently, and tears accumulate.
Irritation and Environmental Triggers
Any source of irritation to one eye can provoke reflex tearing. Common culprits include:
- Ingrown or misdirected lashes rubbing against the cornea on one side
- Chronic eyelid inflammation (blepharitis), which can be asymmetric
- Allergic conjunctivitis that happens to affect one eye more, particularly if you rub or touch that eye more often
- A corneal scratch or foreign body that you may not remember getting
- Airflow exposure, such as sleeping next to a fan or air vent that hits one side of your face
If tearing started suddenly, think about what changed: new eye drops, a different sleeping arrangement, a recent cold or sinus infection, or a minor eye injury. Even certain eye drop preservatives can irritate the surface enough to trigger chronic tearing on the side you use them.
How Doctors Figure Out the Cause
An eye care provider can usually narrow things down with a physical exam and a few simple in-office tests. They’ll look at your eyelid position, check for inflammation or infection, and examine the tiny drainage openings. Two tests are especially useful.
The first measures tear film stability. A drop of fluorescein dye is placed on the eye, and you’re asked to hold your eyes open without blinking. If the tear film breaks apart in less than 10 seconds, dry eye is likely contributing to the problem. The second test checks tear production by tucking a small strip of filter paper under the lower lid for five minutes. Less than 10 millimeters of wetting is below normal; less than 5 millimeters signals a significant production problem.
If a drainage blockage is suspected, the provider may gently flush saline through the drainage system to see where the obstruction lies. Imaging is occasionally needed if there’s concern about a mass or unusual anatomy.
Treatments Based on the Cause
What works depends entirely on why the eye is watering, which is why getting the right diagnosis matters more than trying random remedies.
For dry eye-driven tearing, the goal is to stabilize the baseline tear film so the reflex floods stop. Preservative-free artificial tears, warm compresses to unclog oil glands, and lid hygiene are the first-line approaches. Adjusting your sleep position (switching to your back, or at least off the affected side) can make a measurable difference over time.
For a blocked tear duct, initial treatment in mild cases may involve warm compresses and gentle massage over the tear sac area near the bridge of the nose. If there’s an active infection, antibiotics are needed. The definitive fix for a persistently blocked duct is a surgical procedure called dacryocystorhinostomy, or DCR, which creates a new drainage pathway between the tear sac and the nasal cavity, bypassing the blocked duct entirely. Success rates for this surgery are above 90% with the standard external approach and around 80 to 85% with less invasive techniques done through the nose. The less invasive options generally mean a shorter procedure and no visible scar.
For eyelid malposition like ectropion or entropion, a minor surgical tightening of the lid is often the most effective solution. For irritation from ingrown lashes, removing or redirecting the offending lashes typically resolves the tearing quickly.
Signs That Need Prompt Attention
Persistent one-sided tearing is worth getting checked even if it’s just annoying, because some causes worsen over time. Certain signs warrant a faster visit: painful swelling near the inner corner of the eye (suggesting an infected tear sac), any change in vision alongside the tearing, blood-tinged tears or discharge, or a firm lump that keeps growing. Rarely, a mass in the nasal or sinus area can press on the drainage system and cause one-sided tearing, so unexplained obstruction in an adult is something providers take seriously enough to investigate thoroughly.