The sense of smell is one of the very important senses of human beings. In the history of human evolution, the sense of smell plays an important role in the process of understanding and exploring nature, and at the same time, this sense also brings pleasant enjoyment to people. The loss of sense of smell brings people a lot of trouble. Let’s start with the production of sense of smell. The sense of smell is produced by the olfactory organ and the sensory center. The olfactory organ is composed of the left and right nasal cavities, and the mucous membrane in the nasal cavity is divided into the olfactory area and the respiratory area. The mucous membrane of the olfactory region is distributed in the inner part of the upper turbinate and the mucous membrane of the nasal septum corresponding to it. The mucosa of the olfactory zone contains specific sensory epithelium, i.e. olfactory apparatus and olfactory glands. The secretion of the olfactory glands can dissolve the air-containing particles that reach the olfactory zone and stimulate the olfactory apparatus to produce the sense of smell. The olfactory electrical signals are transmitted step by step through the olfactory nerve to the olfactory center and the external olfactory center to the olfactory area of the brain, where the sense of smell is produced. It means that when we stay in a place with a special smell for a long time, we will be completely adapted to the smell and will not feel it. When the nasal mucosa temporarily loses its sense of smell due to cold, the body’s perception of food taste is weaker than usual; and when people choose their favorite dishes from a table full of dishes, the smell emitted from the dishes is often one of the basic elements that attract people to make their choice. The substances that can cause the sense of smell need to have the following conditions: easily volatile; can dissolve in water; can dissolve in fats and oils. Various pathologies that damage any part of the olfactory pathway can lead to decreased or lost sense of smell. The causes of olfactory decline or loss are as follows: 1. Upper respiratory tract infection: after virus infection, inflammatory reaction may cause nasal obstruction and lead to olfactory loss, which can be recovered completely on its own; however, in some patients, the virus damages the olfactory nerve and olfactory receptors, which is usually very difficult to recover. 2. Rhinitis, sinusitis, nasal polyps, severe nasal septum deviation will block the nasal cavity and prevent the air from entering the olfactory area, which will cause olfactory impairment or loss, but after the blockage is removed, the sense of smell can be restored. However, sometimes less serious head trauma may also cause complete loss of smell. The degree of loss of smell is also related to the location of head trauma. The prognosis of loss of smell due to trauma is poor, and the recovery rate of smell function is less than 10%; 4. Some patients may suffer from olfactory loss after surgery such as nasal septum correction, lateral nasal incision, nasal plastic surgery. This may be caused by intraoperative damage to the nerve or due to local anatomical structure change or scar formation obstructing airflow. Neurosurgery in the anterior fossa of the skull may easily damage the olfactory bulb or olfactory filaments, resulting in total or permanent loss of smell; 8. Patients with total laryngectomy have poor sense of smell because the airflow does not pass through the nasal cavity; 9. Patients with radiotherapy for head and facial tumors, such as nasopharyngeal carcinoma, have significantly reduced sense of smell after radiation therapy, but these patients may gradually recover their sense of smell later.