Obstructive sleep apnoea (OSA) is caused by the muscles and soft tissue in the back of your throat collapsing inwards during sleep.

These muscles support your tongue, tonsils and soft palate (the tissue at the back of the throat used in speech, swallowing and breathing).

Some loss of stability in these muscles and tissues is normal while you sleep, but in most people this doesn't cause any breathing problems.

In cases of OSA, the relaxation of these muscles and soft tissues causes the airway in your throat to narrow or become totally blocked.

This interrupts the oxygen supply to your body, which triggers your brain to pull you out of deep sleep so your airway reopens and you can breathe normally.

Increased risk

There are a number of things that can increase your risk of developing OSA, including:

• being overweight – excessive body fat increases the bulk of soft tissue in the neck, which can place a strain on the throat muscles; excess stomach fat can also lead to breathing difficulties, which can make OSA worse
• being male – it is not known why OSA is more common in men than in women, but it may be related to different patterns of body fat distribution
• being 40 years of age or more – although OSA can occur at any age, it is more common in people who are over 40
• having a large neck – men with a collar size greater than around 43cm (17 inches) have an increased risk of developing OSA
• taking medicines with a sedative effect – such as sleeping tablets or tranquillisers
• having an unusual inner neck structure – such as a narrow airway, large tonsils, adenoids or tongue, or a small lower jaw
• alcohol – drinking alcohol, particularly before going to sleep, can make snoring and sleep apnoea worse
• smoking – you are more likely to develop sleep apnoea if you smoke
• the menopause (in women) – the changes in hormone levels during the menopause may cause the throat muscles to relax more than usual
• having a family history of OSA – there may be genes inherited from your parents that can make you more susceptible to OSA
• nasal congestion – OSA occurs more often in people with nasal congestion, such as a deviated septum (where the tissue in the nose that divides the two nostrils is bent to one side) or nasal polyps, which may be a result of the airways being narrowed