Snoring occurs when airflow through the upper airway is partially blocked. During sleep, all muscles in the body relax, including those in the soft palate (roof of mouth), tongue and throat. This loss in muscle tone during sleep can effectively narrow the upper airway, which obstructs airflow and causes the soft tissue in the airway to vibrate with every breath. Snoring typically only occurs during inhalation, as the expanding lungs sucking the air down reduces the air pressure in the upper airway, pulling the walls of the airway inwards. However, some people snore during expiration, which occurs due to soft tissue fluttering within the upper airway.
Snoring is often louder and more frequent when the snorer is lying on their back compared to their side or front. This is because gravity pulls the tongue backwards, partially blocking the airway.
For snorers with a high BMI, the excess of soft tissue in the upper airway narrows the passage and makes snoring more likely. Aging is another contributing factor to snoring, as the muscles in the upper airway weaken and loosen.
Besides the obvious issues of keeping bed partners or other people in the house awake or the embarrassment of snoring in a public place, loud snoring can indicate sleep apnoea. If the partial obstruction of the upper airway closes over enough, it can trigger an awakening as the body detects it is not getting enough air. This can happen hundreds of times a night for people who suffer from sleep apnoea.
Most people who snore do not have sleep apnoea, but loud snoring or snoring interspersed with silent periods of around 10-90 seconds are indicators of likely sleep apnoea.