The nasal cycle is achieved by selective activation one half of the autonomic nervous system by the hypothalamus. One nasal cavity fossa becomes congested whilst the opposing nasal cavity turbinates are decongested by local vascular shunting. The nasal cycle is also likely linked to ciliary motility which is suspended until the ipsilateral side contrast decongestants. There are also postulated benefits for improved olfactory function.
The nasal cycle affects the nasal turbinates, nasal mucosa and ethmoids but does not appear to affect the maxillary, frontal and sphenoidal sinuses.The overall duration of the cycle is suspected to reflect approximately 2-3 hours. The mucosal cyclical changes have also been demonstrated using MRI imaging demonstrating that both the mucosal volume and T2 signal hyperintensity alternate between the sides of the nasal cavity.
In most this appearance is benign although occasionally patients with fixed septal deviation the nasal cycle may result in intermittent symptomatology of nasal congestion. Recognition of the nasal cycle is important to avoid miscategorisation as nasal congestion or alternate mucosal pathology