The common causes of thick nasal mucus and thick phlegm include bacterial infection secondary to colds, sinusitis, acute bronchitis and so on. 1. Bacterial infection secondary to cold: If bacterial infection is secondary to cold, the symptom of thick nasal mucus and thick phlegm will appear. 2. Sinusitis: bacterial infection caused by nasal congestion, edema, nasal secretions increase, thick nasal discharge can be postnasal drip leakage to the throat, inducing the appearance of thick sputum. 3. Acute bronchitis: when the bronchial tube is infected with bacteria, such as Staphylococcus aureus and Streptococcus pneumoniae infection, thick sputum and thick nasal discharge can appear. Cause thick nasal mucus pus sputum may also have other reasons, such as pneumonia, lung abscess, bronchiectasis, etc. It is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease, and standardized treatment under the guidance of the doctor.