One eye often tears more than the other because the two eyes aren’t perfectly symmetrical. Small differences in tear drainage, eyelid shape, nerve supply, or surface irritation can cause one side to water noticeably more. In most cases the explanation is mechanical: tears are being overproduced on one side, or they’re not draining properly.
How Tear Drainage Works
Tears are produced by a gland above each eye, then spread across the surface every time you blink. From there, they drain through tiny openings (called puncta) at the inner corners of your upper and lower eyelids, flow down narrow channels, collect in a small sac near the bridge of your nose, and finally empty into your nasal passages. That’s why your nose runs when you cry.
Any narrowing or blockage at any point along this path on one side will cause tears to pool and spill over that eyelid. The most common bottleneck in adults is where the drainage channel meets the inside of the nose. Even mild swelling from allergies or a past sinus infection can partially close off one side while the other stays clear. In infants, a thin membrane at the bottom of the channel sometimes hasn’t opened yet at birth, which is why many newborns tear from just one eye for the first several months of life.
Dryness That Triggers More Tears
This sounds contradictory, but a dry eye can actually be a watery eye. When the surface of one eye dries out faster than the other, the irritation triggers a flood of reflex tears to compensate. These emergency tears come on suddenly and in large volume, so the drainage system can’t keep up, and the eye overflows.
Reflex tearing from dryness tends to be intermittent rather than constant. You might notice it more in wind, air conditioning, or after long screen time, and it often affects one eye more because the tear film breaks down unevenly between the two sides. If your watery eye also feels gritty or stings, dryness-driven reflex tearing is a likely culprit. A simple clinical test measures tear production by placing a small paper strip under the lower lid for five minutes. Wetting less than 10 mm generally points toward dry eye, while more than 15 mm is considered normal.
Eyelid Position and Shape
Your eyelids act like windshield wipers, spreading tears evenly and pushing them toward the drainage openings. When one eyelid doesn’t sit flush against the eye, the whole system breaks down on that side.
Ectropion is a condition where the lower eyelid sags outward, pulling away from the eyeball. This exposes more of the eye’s surface, causing dryness and inflammation, while also pulling the drainage opening out of position so tears can’t enter it properly. The result is a chronically watering eye on the affected side. It becomes more common with age as the tissues supporting the eyelid lose elasticity.
The opposite problem, entropion, turns the eyelid inward so that lashes rub against the eye’s surface. That constant scraping triggers pain, redness, and heavy reflex tearing on just one side. Even without full entropion, a few misdirected lashes (a condition called trichiasis) can scratch the cornea enough to make one eye water persistently while the other stays dry.
Blocked or Infected Tear Sac
When the drainage channel becomes fully blocked on one side, tears stagnate in the small sac near the bridge of the nose. Bacteria can grow in that standing fluid, leading to an infection called dacryocystitis. The signs are hard to miss: painful swelling at the inner corner of the eye near the nose, redness, sometimes pus or discharge, and occasionally fever. A chronic, low-grade version of this infection may cause nothing more than a persistently watery eye with mild tenderness, which is easy to overlook.
Nerve-Related Causes
The facial nerve controls both the muscles that help you blink and the signals that tell your salivary glands to produce saliva. After Bell’s palsy, surgery, or trauma to one side of the face, this nerve sometimes heals imperfectly. During recovery, nerve fibers that were supposed to regrow toward the salivary glands can accidentally reconnect to the tear gland instead. The result is a phenomenon sometimes called “crocodile tears”: one eye waters whenever you eat, drink, or even smell food, because the signal meant to trigger saliva is being rerouted to trigger tears. It only affects the side where the nerve was damaged.
Bell’s palsy can also cause one-sided tearing in a more straightforward way. When the muscles on one side of the face are weakened, that eye may not close completely during blinking. Poor lid closure means tears aren’t spread or drained efficiently, so the eye waters and dries out at the same time.
Everyday Irritants and Injuries
Sometimes the explanation is simpler than any underlying condition. A tiny scratch on the cornea, a speck of dust, a loose eyelash, or contact lens irritation on one side will trigger heavy reflex tearing in that eye alone. Allergic reactions can also be asymmetric, especially if you touched one eye after handling a pet or rubbing pollen into it.
People who sleep predominantly on one side sometimes notice more morning tearing or crustiness in the eye that was pressed against the pillow, because pressure on the eyelid disrupts the tear film overnight. Similarly, sitting next to a fan or air vent that blows across one side of your face can dry out that eye and provoke reflex tearing throughout the day.
When One-Sided Tearing Needs Attention
Occasional asymmetric tearing, especially in cold or windy weather, is normal and rarely a concern. But persistent one-sided watering that lasts weeks deserves a closer look, particularly if it’s paired with other symptoms. Vision changes, pain around the eye, a growing lump near the bridge of the nose, or the constant sensation that something is stuck in your eye are all signs that point toward a structural or infectious problem rather than simple irritation. Bloody or discolored tears, or tearing that started after facial surgery or a bout of Bell’s palsy, also warrant evaluation to check the drainage pathway and nerve function on that side.