A child’s nosebleed when blowing the air conditioner may be caused by too dry air, allergic rhinitis and deviated nasal septum. 1. The air is too dry: it may be due to the fact that when the air conditioner is turned on indoors, the humidity inside the room will be reduced and the dryness of the air inside the room will be increased, which leads to fast evaporation of water from the mucous membrane of the child’s nasal cavity and can easily induce the dryness of the mucous membrane of the nasal cavity, which can trigger the phenomenon that the child will have a nosebleed when he or she blows on the air conditioner. 2. Allergic rhinitis: if the child suffers from allergic rhinitis, and open the air conditioning may aggravate the child’s symptoms of nasal congestion, sneezing and runny nose, the nasal mucosa is more fragile, if often blowing the nose or picking the nose, etc., which may lead to the symptoms of nosebleed when blowing the air conditioning. 3. Deviated septum: If the child suffers from deviated septum, the mucous membrane in the deviated place is relatively thin, and the air-conditioning evaporates the moisture in the room, which can easily lead to nasal mucous membrane ulceration, erosion, etc., which can make the submucosal blood vessels rupture and bleed. Children blowing air-conditioning nosebleed, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.