Align Health Library
What Is Sleep Apnoea? Understanding OSA in Adults
Sleep apnoea is a common condition in which your breathing repeatedly stops and starts while you sleep. The most common type, obstructive sleep apnoea (OSA), happens when the airway at the back of the throat narrows or closes during sleep. Many people who have it don't know.
What is sleep apnoea?
Sleep apnoea (also spelled "sleep apnea") is a sleep-related breathing disorder. During the night, breathing repeatedly pauses or becomes very shallow, then restarts, often with a gasp or snort.
These pauses can happen many times an hour. Each one interrupts your sleep and can lower the oxygen level in your blood, even if you sleep through it.
There are two main types: obstructive sleep apnoea, which is by far the most common, and central sleep apnoea. This guide focuses mainly on obstructive sleep apnoea in adults.
What happens to your breathing during sleep?
When you are awake, the muscles around your throat hold your airway open. As you fall asleep, these muscles naturally relax. For most people, the airway still stays open enough to breathe freely.
In someone with OSA, the relaxed tongue and soft tissues fall back and narrow the airway. As airflow drops, the oxygen level in the blood falls. The brain senses the problem and briefly rouses you, just enough to tighten the throat muscles and reopen the airway, often with a gasp, snort or choking sound.
Because these awakenings last only seconds, most people have no memory of them. They simply wake up feeling as if they haven't slept well.
The cycle, repeated through the night
- Airway relaxes and narrows
- Breathing slows or stops
- Oxygen drops and the brain briefly wakes you
- Airway reopens and you fall back asleep, and the cycle can begin again
How does the airway become blocked?
The upper airway is a soft, flexible tube with no rigid support, running from behind the nose down to the voice box. During sleep, it can narrow or collapse at one or more points.
- The soft palate and uvula at the back of the roof of the mouth
- The tonsils, if they are enlarged
- The base of the tongue, which can fall backwards, especially when lying on your back
- The side walls of the throat, which can be thicker with extra weight around the neck
How easily the airway collapses depends on its size and shape and on the tissues around it. Jaw size and position play an important role: a smaller or set-back lower jaw leaves less room for the tongue. Research suggests facial bone structure is an especially important factor in many Asian patients, which is why sleep apnoea can occur in people who are not overweight.
Other risk factors include weight, age, nasal blockage and alcohol. These are covered in detail in our guide to sleep apnoea symptoms and risk factors.
Apnoea
Breathing stops completely for 10 seconds or more.
Hypopnoea
Breathing becomes much shallower for 10 seconds or more, with a drop in oxygen or a brief awakening.
Doctors use these two terms to describe the breathing events counted during a sleep study.
Obstructive vs central sleep apnoea
Both types cause pauses in breathing during sleep, but for different reasons.
| Compared | Obstructive sleep apnoea (OSA) | Central sleep apnoea |
|---|---|---|
| What happens | The airway narrows or closes, so air cannot flow freely | The brain briefly fails to send the signal to breathe |
| Breathing effort | The chest and belly keep trying to breathe against the blockage | There is little or no effort to breathe during the pause |
| How common | By far the most common type | Much less common |
| Often linked with | Airway and jaw anatomy, weight, age, nasal blockage | Heart failure, stroke, some medications such as opioids, and high altitude |
| Snoring | Usually present | Less typical |
Some people have features of both, which is sometimes called mixed sleep apnoea. A sleep study is the only reliable way to tell the types apart, and this matters because they are managed differently.
How is sleep apnoea severity measured?
During a sleep study, the number of apnoeas and hypopnoeas is counted and averaged over each hour of sleep. This is called the apnoea-hypopnoea index (AHI), and it is the main way severity is described.
For example, an AHI of 20 means breathing was reduced or interrupted an average of 20 times every hour, which falls in the moderate range.
| Severity | Breathing events per hour (AHI) |
|---|---|
| Normal | Fewer than 5 |
| Mild | 5 to 14 |
| Moderate | 15 to 29 |
| Severe | 30 or more |
Severity is only part of the picture. Your doctor will also consider how low your oxygen levels fall, how sleepy you feel during the day and your other health conditions. Together, these help decide which treatment suits you best.
Why sleep apnoea deserves attention
Sleep apnoea is more than a disturbed night. Repeated drops in oxygen and constantly broken sleep put ongoing strain on the body.
Untreated, it is associated with high blood pressure, heart disease, stroke and type 2 diabetes, as well as poor concentration, low mood and a higher risk of accidents caused by drowsiness.
These are increased risks, not certainties, and treatment can make a real difference to how you feel.
How Align Dental Surgery can help
Dentists are often among the first to notice possible signs of sleep apnoea, because we examine the teeth, jaws, tongue and throat at every visit. Worn teeth from grinding, a scalloped tongue or a narrow jaw can all prompt a conversation about sleep.
A dental examination cannot diagnose sleep apnoea. Our role is to screen for signs, refer you to an ENT specialist for medical assessment and a sleep study where appropriate, and work with your specialist on treatment.
If a custom-made oral appliance is suitable for you, we can design, fit and monitor it.
Explore our sleep apnoea series
This guide is the first in our series on sleep apnoea in adults. The next guide is ready to read; the rest are being prepared.
In preparation
- How does sleep apnoea affect your health?
- Sleep apnoea in men and women
- How is sleep apnoea diagnosed?
- Sleep apnoea treatment options in Singapore
- Mandibular advancement devices
- Snoring or sleep apnoea?
Questions & answers
Common questions
Is sleep apnoea common?
Can I have sleep apnoea without knowing it?
Is sleep apnoea the same as snoring?
Is sleep apnoea serious?
Can sleep apnoea be treated?
Can a dentist tell me whether I have sleep apnoea?
Does this guide apply to children?
Sources
References & further reading
The research behind this guide, with links to the original papers and health authorities where they are publicly available. Ask us at your next visit if you would like to know more about any of these studies.
- Leow LC, et al. Singapore consensus statements on the management of obstructive sleep apnoea. Annals of the Academy of Medicine, Singapore. 2025;54(10):627-643.
- Tan A, et al. Prevalence of sleep-disordered breathing in a multiethnic Asian population in Singapore: a community-based study. Respirology. 2016;21(5):943-950.
- Lee RWW, et al. Differences in craniofacial structures and obesity in Caucasian and Chinese patients with obstructive sleep apnea. Sleep. 2010;33(8):1075-1080.
- Yeghiazarians Y, et al. Obstructive sleep apnea and cardiovascular disease: a scientific statement from the American Heart Association. Circulation. 2021;144(3):e56-e67.
- National Heart, Lung, and Blood Institute. What is sleep apnea?
- National Heart, Lung, and Blood Institute. How sleep apnea is diagnosed.
- SingHealth. Obstructive sleep apnoea (OSA).
Links open in a new tab on the publisher's own website.
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