The olfactory nerve is the nerve fiber that runs from the olfactory epithelium through the sieve plate to the olfactory bulb. The ability to smell is a characteristic of the olfactory cells in the nasal mucosa. Injury to the nasal mucosa, olfactory bulb, olfactory filaments or central nervous system connections may affect the sense of smell. Clinical manifestations are hyposmia, olfactory loss, olfactory absence, olfactory inversion, phantom smell and increased sensitivity to olfactory stimuli. Early detection and early treatment are necessary in daily life, of which the clinical examination methods are mainly as follows. 1.Cerebrospinal fluid examination. 2.Other necessary selective examination items, such as blood routine, blood electrolytes, blood sugar, urea nitrogen, etc. 3.Bottom radiography, cranial CT and MRI examination. 4.Ear, nose and throat examination and olfactory examination. 5.Other necessary selective auxiliary examination items include chest X-ray, electrocardiogram, etc. Patients with olfactory allergy usually do not affect their daily work and study. Patients with olfactory allergy should be further examined for the cause and treated for the right reason. Patients with olfactory allergy are less common, but according to the cases that have been reported, patients are so sensitive to olfactory stimuli that it becomes the source of discomfort.