Obstructive sleep apnoeas are due to transient closure of the upper airway during sleep and merge into hypopnoeas in which the airway narrows, but some airflow continues. They are due to the forces compressing the airway overcoming those which stabilise its patency. The commonest association is obesity in which fatty tissue is deposited around the airway. Exercise has been recommended as a method of losing weight, but other techniques which achieve this are also thought to improve symptoms due to sleep apnoeas. Sleep hygiene may alter the sleep structure and the control of the upper airway during sleep and thus promote its patency.