Loss of sense of smell can be caused by head and facial nerve injury, nasal diseases or upper respiratory tract infections. 1. Head and face injuries: common accidents such as car accidents, falls, resulting in head and face injuries such as fracture of the anterior part of the base of the skull, may lead to damage to the olfactory nerves, resulting in damage to the sense of smell, and irreversible loss of the sense of smell. 2. Nasal diseases: allergic rhinitis, sinusitis, nasal polyps and other nasal diseases can cause irritation to the nasal mucosa, causing inflammation of the nasal mucosa and olfactory nerve, which can also lead to loss of sense of smell. 3. Upper respiratory tract infections: common upper respiratory tract infections and influenza, due to viral attack, can also lead to the olfactory nerve inflammatory edema or functional abnormalities, loss of smell. There are many reasons for the loss of sense of smell, it is recommended to go to the hospital in time for examination, after clarifying the cause of the disease, under the guidance of a professional doctor, combined with the personal situation of targeted treatment, to avoid misunderstanding the condition, aggravate the symptoms and cause serious impact.