Nosebleeds from the left nostril of an 8-year-old boy can be caused by a variety of reasons, including broken capillaries, foreign bodies in the nasal cavity, inflammation of the nose and hematologic disorders. Most of them are treated with medication and foreign body removal. 1. Capillary rupture: if the nasal cavity is too dry or often digging the nostrils can easily lead to nasal capillary rupture and cause bleeding, you can use your fingers to press both sides of the nose to stop bleeding, and use saline nasal spray to keep the mucous membrane clean and moist. 2. Nasal foreign body: unilateral bleeding in children’s nasal cavity is usually caused by nasal foreign bodies that have been stored in the nasal cavity for a long time, and it is recommended to go to the hospital for nasal endoscopy and take out the foreign body. 3. Nasal inflammation: if the patient suffers from rhinitis or sinusitis and other diseases, you can use physiological sea saline, mometasone furoate nasal spray and other drugs under the guidance of the doctor for treatment. 4. Blood system diseases: such as structural and functional defective diseases of blood vessel wall, platelet count or dysfunctional diseases and coagulation factor disorders, etc. It is recommended that the patients should take more vitamins, transfuse platelets and coagulation factors, etc. and go to the hematology department of the hospital in time for systematic treatment. All of the above drugs should be used under the guidance of a doctor, avoid self-medication. 8-year-old boy unilateral nostril bleeding may also be other causes, it is recommended to consult a doctor in a timely manner, improve the relevant examination, and targeted treatment or treatment.