The sense of smell is one of the very important senses of human beings, the sense of smell in the history of human evolution of human beings to understand and explore the process of nature plays an important role, at the same time, this feeling also gives people a pleasant enjoyment. Often in life, because of the cold, eat anything tasteless, the loss of sense of smell to bring people a lot of trouble, then why the sense of smell will be lost? Let’s start with the production of the sense of smell. The human sense of smell is produced by the olfactory organ and the sensory center, the olfactory organ consists of the left and right nasal cavity, the mucous membrane of the nasal cavity is divided into the olfactory area and respiratory area. The mucous membrane of the olfactory region is distributed in the inner side of the upper turbinate and the mucous membrane of the nasal septum corresponding to it. The mucosa of the olfactory region contains specific sensory epithelium, i.e., olfactory apparatus and olfactory glands, and the secretions of the olfactory glands can dissolve the air-containing particles that reach the olfactory region and stimulate the olfactory apparatus to produce the sense of smell. The electrical signals of olfaction are transmitted to the olfactory center and the external olfactory center through the olfactory nerve step by step, until the olfactory area of the brain, which produces the sense of smell. The sense of smell has a characteristic, the ancients said: into the room of orchids, for a long time and do not smell its fragrance, meaning that when we stay in a place with a special smell for a long time, the smell will be completely adapted to no feeling, this phenomenon is called the olfactory organs to adapt to the smell organs will also have a sense of taste. When the nasal mucosa due to colds and temporary loss of smell, the human body on the food flavor perception is weaker than usual; and people in the table full of dishes to choose their favorite dishes, dishes emitting the smell, often attract people to make a choice of one of the basic elements. Can cause the sense of smell of substances need to have the following conditions: easy to volatile; can be dissolved in water; can be dissolved in oil. Various lesions that damage any part of the olfactory production and conduction pathway can lead to a decrease or loss of the sense of smell. Life is often the decline or loss of smell can be seen as follows: 1, upper respiratory tract infection: viral infection, inflammatory reaction, can cause nasal obstruction leading to decreased sense of smell, this sense of smell decline can be completely recovered most of the time; but there are some patients, the virus damage to the olfactory nerves, olfactory receptors are damaged, usually this type of olfactory disorders is very difficult to recover; 2, nasal and sinus obstruction disease: suffering from Rhinitis, sinusitis, nasal polyps, severe nasal septum deviation will block the nasal cavity, so that the air can not enter the olfactory region, causing smell loss or loss, but after lifting the obstruction, the sense of smell can be restored in general; 3, head trauma: the incidence of olfactory dysfunction after head trauma is 4% – 10%, the degree of loss of sense of smell is generally related to the severity of the trauma. However, sometimes less serious head trauma can also cause complete loss of smell. The degree of head trauma is also related to the part of head trauma, and the prognosis of olfactory loss caused by trauma is poor, and the recovery rate of olfactory function is less than 10%; 4, toxicity: inhalation of toxic heavy metal dust, adsorption in the nasal mucous membrane will affect the olfactory function of the local nutritional deficiencies; 5, organ degradation: the loss of sense of smell of elderly people can be caused by the degradation of the organ function; 6, the nasal cavity, sinus tumors will block the airflow affecting the sense of smell: such as intracranial tumors such as meningiomas, pituitary tumors will cause the olfactory nerve to be affected. Pituitary tumors can cause local damage to the olfactory organs such as olfactory nerve and olfactory bulb; 7, some patients with post-surgery such as nasal septum correction, nasal lateral incision, rhinoplasty and so on cause olfactory hyposmia: the reason may be the damage to the nerves during the operation or due to the change of the local anatomical structure, the formation of scars that impede the airflow. Neurosurgery of anterior cranial fossa is often easy to damage the olfactory bulb or olfactory filament, resulting in total and permanent loss of sense of smell; 8, total laryngectomy patients with poor sense of smell for the patient’s respiratory airflow does not pass through the nasal cavity of the reason; 9, head and face tumors after radiotherapy: such as nasopharyngeal carcinoma and other patients with olfactory sense of smell after radiation therapy appeared to have a significant decrease in the sense of smell, but the sense of smell of this part of the patient’s future may be gradually restored.