The nasolacrimal duct is a small tear duct above and below the inner canthus of the human eye, which converges into a tear duct, enters the tear sac, and then follows the lateral wall of the nasal cavity down to the entire duct of the lower nasal passage, mainly used to collect tears, the tears secreted in the eye enter the nasolacrimal duct from the tear duct, flow in from the nasal cavity, and swing with the cilia to the nasopharynx. If the nose is blocked by snot when you have a cold, the nasolacrimal duct will be blocked and your eyes will show tears, or if you cry a lot, the nasolacrimal duct will swell and cause a snotty nose and tears.