Chronic Sinusitis: This condition is characterized by persistent inflammation of the sinuses, often due to bacterial, viral, or fungal infections. The foul smell can be attributed to the accumulation of pus and debris in the sinuses. Chronic sinusitis is a common condition that can cause foul-smelling nasal drainage due to the bacterial breakdown of sinus secretions.

Nasal Foreign Body: Especially in children, a foreign object lodged in the nasal cavity can cause a foul odor due to the accumulation of bacteria and debris around the object.
Rhinoscleroma: A chronic granulomatous infection caused by Klebsiella rhinoscleromatis, which can lead to the destruction of nasal tissue and the production of foul-smelling discharge.
Atrophic Rhinitis: Characterized by atrophy of the nasal mucosa and turbinate bones, leading to the accumulation of foul-smelling crusts within the nasal cavity.

Malignant Tumors: Although rare, tumors such as squamous cell carcinoma or adenocarcinoma in the nasal cavity or sinuses can cause foul-smelling discharge due to tissue necrosis.
Invasive Fungal Sinusitis: Especially in immunocompromised patients, fungal infections like mucormycosis can invade the sinuses and cause necrosis, leading to foul-smelling discharge.
Cerebrospinal Fluid (CSF) Leak: A leak of CSF into the nasal cavity can become infected, leading to foul-smelling drainage. This condition requires prompt diagnosis and treatment to prevent meningitis.

Trimethylaminuria (Fish Odor Syndrome): A rare genetic disorder that causes the body to be unable to break down trimethylamine, leading to a fish-like odor in bodily secretions, including nasal discharge.
Bronchiectasis: A condition characterized by the irreversible dilation of parts of the airways, which can lead to chronic infections and foul-smelling sputum or nasal discharge if the disease process extends to the sinuses.
Nasal Syphilis: A manifestation of tertiary syphilis that can cause destruction of the nasal septum and turbinates, leading to foul-smelling discharge.