Smelly nasal mucus may be related to nasal foreign body, nasal tumor, sinusitis and other reasons. 1. Nasal foreign body: if children stuffed into the nasal cavity foreign body or surgery residual foreign body can not be degraded in the nasal cavity and sinus, secondary bacterial infection, will secrete thick nasal mucus or thick bloody nasal mucus, usually accompanied by a bad smell. 2. Nasal tumor: If malignant tumor occurs in the nasal cavity, during the process of tumor proliferation and development, the environment of the nasal cavity changes, pathogenic microbial infections, and the nasal discharge will also be accompanied by malodorous smell. 3. Sinusitis: generally due to bacterial, viral, fungal infection caused by inflammation of the mucous membrane of the sinus, especially the odontogenic maxillary sinusitis, the nasal discharge will appear obvious odor. When the nasal mucus odor, need to actively seek medical attention systematic examination to clarify the diagnosis.