German physician Richard Kayser first described the nasal cycle in 1895. He observed the alternate congestion and decongestion of blood-filled erectile tissue in the nasal turbinates. The duration of this cycle ranges from 40 minutes to several hours in normal nasal passages and allows the human to physiologically have two noses. The nasal cycle is controlled by the autonomic nervous system. There are several reasons postulated for the existence of the nasal cycle. Switching of airflow between nostrils prevents excessive drying, crusting and infection that would occur if the airflow were static. The switching mechanism and engorgement of the erectile tissue operates as a periodic pump to generate plasma exudate important for respiratory defense mechanisms. Scent molecules degrade and are absorbed at different rates allowing easier detection of some smells in the fast moving airflow and others in the slower airflow. It was observed that in the lying position the dependent nasal fossa was engorged and it is postulated that this causes the person to alternate sides when sleeping.

A good reason in choosing the most patent nostril at the time of intubation!