Nose unilateral flow of yellow water seen in unilateral sinusitis, sinus mucosal cysts, cold secondary bacterial infection. 1. Unilateral sinusitis: rhinitis, nasal septum deviation, nasal swelling and other nasal diseases, can lead to blockage of the affected side of the nasal cavity, affecting the sinus drainage, and over time it is easy to induce sinusitis, which is often manifested in the flow of yellow pus nasal mucus, nasal congestion, headache and other symptoms. 2. Sinus mucous membrane cysts: sinus cysts can grow gradually, to a certain extent, can rupture, yellow watery cystic fluid can be through the sinus outflow from the nasal cavity. 3. Cold and flu secondary bacterial infection: after a cold and flu, if a side of the nasal cavity bacterial infection, due to the bacteria lead to inflammatory reaction, and the symptoms of yellow pus nasal discharge. It is recommended to consult a doctor in time to find out the cause, and actively treat the disease according to the cause to avoid aggravation of the condition.