During outpatient consultations, we sometimes hear patients complaining that their sense of smell is not working. Some of them have worse sense of smell than before – decreased sense of smell; some of them have lost sense of smell – loss of smell; some of them have smelled odors that do not exist in the environment – phantom smell. As there are many causes of olfactory disorder, it may be a precursor of intracranial or nasal pathology or mental illness. It is generally divided into respiratory olfactory disorder, neurological olfactory disorder, and psychiatric olfactory disorder. Loss of sense of smell is a gradual process. Polyps, tumors or enlarged turbinates caused by chronic rhinitis can cause the air containing odor molecules from outside to enter the olfactory area of the nose. The mucous membrane of the olfactory area contains a large number of olfactory cells, which can sense odors and transmit information through olfactory nerves (olfactory filaments) to the olfactory bulb and olfactory center in the skull. In patients with chronic sinusitis, the olfactory area is occupied by pus and polyps, which can also cause olfactory disturbance, and these are respiratory olfactory disturbances, often accompanied by nasal congestion. And atrophic rhinitis, olfactory neuritis and lack of niacin, vitamin B12, iron, zinc and other nutrients can also cause olfactory sensory impairment, resulting in decreased sense of smell, they are often neurological (sensory) olfactory disorders. The inability to smell on one or both sides along with the feeling of chronic headache and mental disturbance may be due to a tumor at the base of the skull compressing the olfactory nerve, which needs extra attention. Intracranial fractures, contusions, and hematomas can damage the olfactory nerve, mostly immediately. Chemical gas damage can also cause a rapid loss of smell. In our clinic, we have also met some patients who have lost their sense of smell after catching a cold, but their sense of smell has not recovered or even disappeared after one or two weeks. This may be due to the destruction of olfactory cells and olfactory nerves caused by viral infection. In allergic rhinitis patients, the mucous membrane of the olfactory area often becomes edematous during the allergic attack, causing temporary respiratory smell disorder. However, when the disease is prolonged, olfactory nerve sheath edema and mucosal degeneration in the olfactory area may cause permanent olfactory impairment. Chronic sinusitis also has similar manifestations. Patients with olfactory disorder should go to hospital for examination to find the cause and treatment, especially to exclude intracranial tumors. Respiratory olfactory disorder is easily treated by removing nasal polyps, treating sinusitis, and trimming enlarged turbinates. Allergic rhinitis should be treated with reasonable medication to control symptoms and eliminate mucosal edema. Neurological olfactory disorder caused by cold, olfactory neuritis and atrophic rhinitis should be treated as early as possible. Anti-viral drugs, neurotrophic drugs, multivitamins and trace elements can be given as appropriate. Of course, there are some patients who can’t find any cause and have no major problems, but just have some inconvenience in life and have a bad meal.