Blocked tear ducts can happen at any age, from birth to adulthood. Causes include:
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Blockage at birth. Many infants are born with blocked tear ducts. The tear drainage system may not be fully developed or there may be a problem with a duct. Often, a thin tissue membrane remains over the opening that empties into the nose, called the nasolacrimal duct.
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Age-related changes. As people age, the tiny openings that drain tears, called puncta, may get narrower, causing blockage.
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Infection or inflammation. Long-standing infection or inflammation of the eyes, tear drainage system or nose can cause the tear ducts to become blocked.
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Injury or trauma. An injury to the face can cause bone damage or scarring near the drainage system. This can affect the typical flow of tears through the ducts. Even small particles of dirt or loose skin cells lodged in the duct can cause blockage.
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Tumor. A tumor in the nose or anywhere along the tear drainage system can cause blockage.
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Eye drops. Rarely, long-term use of certain medicines, such as eye drops used to treat glaucoma, can cause a blocked tear duct.
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Cancer treatments. A blocked tear duct is a possible side effect of chemotherapy medicine and radiation treatment for cancer.
How the tear drainage system works
The lacrimal glands produce most of the eyes' tears. These glands are located inside the upper lids above each eye. Typically, tears flow from the lacrimal glands over the surface of the eye. Tears drain into openings called puncta on the inside corners of the upper and lower eyelids.
The puncta lead to small canals called canaliculi. Canaliculi move tears to a sac on the side of the nose called the lacrimal sac. From there, tears travel down the nasolacrimal duct and drain into the nose. Once in the nose, tears are absorbed again.
A blockage can happen at any point in the tear drainage system, from the puncta to the nose. When that happens, tears don't drain properly, causing watery eyes and increasing the risk of eye infections and irritation.