Left-sided nosebleed, i.e. unilateral nosebleed, needs to be alerted to deviated nasal septum, rhinitis, nasopharyngeal tumors and so on. 1. Deviated nasal septum: Because the deviated part is prone to vascular deformity, and the mucous membrane here is relatively thin, when stimulated by airflow, dust and other stimuli, it is easy to break, resulting in nose bleeding. If the septum is deviated to the left, it can be manifested as bleeding from the left side of the nose. 2. Rhinitis: For example, chronic dry rhinitis, acute rhinitis, allergic rhinitis, etc., the inflammatory medium will cause damage to the mucous membrane of the nasal cavity, resulting in vasodilatation, rupture, which in turn causes nose bleeding. And rhinitis will also cause nose itching, nasal congestion and other uncomfortable symptoms, it is easy to prompt patients to pick their noses, resulting in nasal bleeding. 3. Nasopharyngeal tumor: for example, hemangioma in nasopharynx, when the tumor ruptures, it will cause nose bleeding. Nasopharyngeal cancer invades the surrounding blood vessels, which will also cause a lot of nosebleeds, especially unilateral nosebleeds. If nosebleeds occur frequently on the left side, it is recommended to go to regular hospitals in time for clear diagnosis and treatment.