Obstructive sleep apnea is caused by a complete obstruction of the airway, as opposed to partial obstruction.  Obstructive sleep apnea is the most severe and most common form of sleep apnea, and occurs in about two percent of woman and four percent of men over the age of 35.

The exact cause of obstructive sleep apnea is not clear, but the site of the obstruction in most patients is the soft palate, extending to the region at the base of the tongue.  There are no rigid structures, such as cartilage or bone, in this area to hold the airway open. During the day, muscles in the region keep the passage wide open.  But as a person with obstructive sleep apnea falls asleep, these muscles relax to a point where the airway collapses and becomes obstructed, causing the breathing episodes and snoring.  When the airway closes, breathing stops and the sleeper awakens to open the airway.  The arousal from sleep usually lasts only a few seconds, but brief arousals disrupt continuous sleep and prevent the person from reaching the deep stages of slumber, therefore leaving them tired and irritable.  Once normal breathing is restored, the person with the obstructive sleep apnea disorder falls asleep only to repeat the cycle throughout the night.