There are many reasons why there is yellow snot in the nose and it smells bad, and the common reasons are acute sinusitis, nasal foreign body, odontogenic maxillary sinusitis, etc. 1. Acute sinusitis: caused by acute rhinitis, an acute purulent infection of the sinus mucosa, the main clinical manifestations of nasal congestion, pus flow, facial pain, olfactory disorders, can be accompanied by chills, fever, general discomfort. 2. Nasal foreign body: most common in children, when parents do not pay attention, play mistakenly peanuts, soy, small toys and other foreign objects into the nasal cavity, the foreign body remains in the nasal cavity for a long time, resulting in nasal infection, if anaerobic infection occurs after the occurrence of yellow runny nose, accompanied by a foul odor. 3. Odontogenic maxillary sinusitis: maxillary sinusitis caused by inflammatory lesions of the teeth, the main clinical manifestations of nasal congestion, runny nose, foul odor, accompanied by toothache, nose swelling, headache and so on. There are other causes of yellow snot in the nose, such as fungal rhinitis, nasal tumors, etc. It is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.