In some patients with colds, they cannot smell, which is caused by the failure of the olfactory cells of the nasal mucosa. When the upper respiratory tract mucosa is infected by viruses, bacteria and other pathogens, there will be obvious congestion, edema and large amount of inflammatory secretions in the nasal mucosa. At this time, the secretions and edema will block the connection between the olfactory cells of the nasal mucosa and the outside world, resulting in a loss of smell and the nasal cavity cannot smell anything. Generally, after symptomatic treatment to reduce the congestion and edema of nasal mucosa and inflammatory secretion exudation, the sense of smell will slowly recover and the normal physiological function of smell can be restored after the symptoms of cold improve.