Why Is One Eye Watering?

Most asymmetric watering has a straightforward anatomical explanation. The tear drainage system on each side works independently, and a partial or complete blockage on one side causes that eye to overflow while the other drains normally. Eyelid position, localised dryness, and unilateral irritation can all produce the same asymmetric pattern. Very rarely, unilateral watering accompanies something that needs prompt attention, but the key warning signs are clearly distinguishable from simple drainage problems.

Tears from each eye drain independently. From the surface of the eye, tears flow toward two tiny openings (the puncta) at the inner corner of each eyelid, one on the upper lid, one on the lower. These lead into small tubes (the canaliculi) that join and empty into the lacrimal sac, which connects to the nasolacrimal duct and eventually drains into the back of the nose. This entire pathway exists as a mirrored pair: one for each eye. If the system on one side becomes partially blocked, through scarring, narrowing with age, or inflammation, that eye will water while the other remains dry. This is one of the most common explanations for asymmetric watering, and it is very amenable to treatment when the blockage is clearly established.

For more detail, see blocked tear duct and watery eyes explained.

The puncta (the openings through which tears drain) only work correctly when they are in contact with the eye's surface. Each time you blink, the punctum on the lower lid dips into the tear lake at the inner corner and draws tears into the drainage system. If the lower eyelid on one side turns slightly outward, even by a small degree, the punctum on that side loses its position against the eye and tears overflow onto the cheek instead of draining. This is called ectropion when the lid turns outward, and its mildest forms can be almost invisible to the patient. Similarly, if one lower eyelid has slightly less tone than the other (which becomes increasingly common with age), the drainage on that side becomes less efficient. Eyelid laxity is one of the subtler and more commonly overlooked causes of asymmetric watering.

See ectropion and entropion for more detail.

Dry eye is often considered a symmetric condition, but it can and does affect one eye more than the other. If one eye has a less stable tear film, it will be more prone to reflex tearing, the paradoxical flood of compensatory tears that the eye produces in response to surface dryness and irritation. Localised irritation can also produce one-sided watering: a small particle trapped under the eyelid, an ingrown eyelash, or a localised area of conjunctival inflammation may all cause one eye to water persistently without affecting the other. These causes tend to produce a grittier, more irritable sensation alongside the watering.

In the great majority of cases, one watery eye has a benign cause and can be fully assessed at a routine ophthalmology appointment. Persistent watering that is affecting quality of life is always worth investigating, not because it is dangerous, but because many of the common causes respond very well to treatment.

Last medically reviewed: May 2026