*
nasal and sinus disease (e.g., allergic or vasomotor rhinitis, chronic sinusitis,
nasal polyps, adenoid hypertrophy)
* upper respiratory infection
* head trauma (e.g., frontal skull fracture, occipital injury, nasal fracture)
* cigarette smoking
* neurodegenerative disease (e.g., Alzheimer's disease, Parkinson's disease, multiple sclerosis)
* increasing age
Less common causes include
* drug induced - see linked item
* cocaine abuse (intranasal)
* toxic chemical exposure (e.g.