What Is Sleep Apnea? Causes, Symptoms, and Treatment Explained
Sleep apnea is a disorder in which breathing repeatedly stops and restarts during sleep. These pauses can last from a few seconds to more than a minute and may occur dozens or even hundreds of times per night. Because each interruption partially wakes the brain — often without the sleeper being aware — sleep apnea fragments rest, prevents deep sleep stages, and puts sustained stress on the cardiovascular system. It is one of the most common sleep disorders, yet it remains significantly underdiagnosed.
Types of Sleep Apnea
There are three recognized forms, each with a different underlying mechanism.
Obstructive sleep apnea (OSA) is by far the most prevalent type, accounting for the majority of diagnoses. It occurs when the muscles in the throat relax during sleep, causing the soft tissue at the back of the airway — including the soft palate, uvula, and tongue — to collapse and partially or completely block airflow. The brain eventually registers the oxygen drop and rouses the body enough to reopen the airway, usually with a gasp, snort, or brief awakening.
Central sleep apnea (CSA) involves no physical obstruction. Instead, the brain fails to send the correct signals to the muscles that control breathing. This is less common and more often associated with underlying neurological conditions, heart failure, or opioid use.
Complex sleep apnea syndrome (also called treatment-emergent central sleep apnea) is a combination of both types, sometimes appearing in patients who develop central apnea after beginning treatment for obstructive apnea.
Risk Factors and Causes
Obstructive sleep apnea has several well-established risk factors:
- Excess weight — Fat deposits around the upper airway can obstruct breathing. Obesity is the single strongest modifiable risk factor for OSA.
- Anatomy — A naturally narrow airway, enlarged tonsils or adenoids, a recessed jaw, or a large neck circumference all increase risk.
- Age — The muscles controlling the airway lose tone with age; OSA prevalence increases significantly in middle age and beyond.
- Sex — Men are diagnosed with OSA at roughly twice the rate of women, though the gap narrows after menopause.
- Alcohol and sedatives — These substances relax throat muscles and can worsen or trigger apnea events.
- Smoking — Increases inflammation and fluid retention in the upper airway.
- Family history — Genetic factors influencing airway anatomy and neurological control of breathing contribute to risk.
Symptoms
The hallmark symptom of obstructive sleep apnea is loud, chronic snoring — but not everyone who snores has apnea, and not everyone with apnea snores noticeably. More telling signs include:
- Witnessed pauses in breathing during sleep (often reported by a partner)
- Gasping or choking during the night
- Waking with a dry mouth or sore throat
- Morning headaches (caused by overnight drops in blood oxygen)
- Excessive daytime sleepiness despite a full night in bed
- Difficulty concentrating, memory problems, or irritability
- Frequent nighttime urination
Because many of these symptoms can be attributed to other causes, sleep apnea often goes unrecognized for years. Untreated OSA is associated with elevated risk of hypertension, type 2 diabetes, stroke, heart attack, and atrial fibrillation — the mechanism being the repeated oxygen desaturations and stress-hormone surges that accompany each apnea event.
Diagnosis
The standard diagnostic tool is a polysomnography (PSG), commonly called a sleep study. Conducted overnight in a sleep lab, it measures brain activity, eye movements, muscle activity, heart rate, oxygen saturation, airflow, and breathing effort simultaneously. Technicians count apnea events (complete cessation of airflow) and hypopnea events (partial reduction) to calculate an Apnea-Hypopnea Index (AHI):
| AHI (events per hour) | Severity |
|---|---|
| < 5 | Normal |
| 5–14 | Mild |
| 15–29 | Moderate |
| ≥ 30 | Severe |
Home sleep apnea tests (HSATs) are simpler, cheaper devices that measure airflow, effort, and oxygen saturation at home. They are increasingly used for straightforward OSA diagnosis but are less comprehensive than full lab studies and cannot reliably diagnose central or complex apnea.
Treatment Options
Treatment depends on severity and type.
Continuous positive airway pressure (CPAP) therapy is the first-line treatment for moderate-to-severe OSA. A CPAP machine delivers a continuous stream of pressurized air through a mask worn during sleep, acting as a pneumatic splint that keeps the airway open. When used consistently, CPAP eliminates most apnea events, improves sleep quality, reduces daytime sleepiness, and lowers cardiovascular risk. Adherence is the main challenge — masks must be properly fitted and the pressure setting adjusted to the individual.
Oral appliance therapy uses a custom-fitted mouthguard that repositions the jaw and tongue to keep the airway open. It is less effective than CPAP for severe apnea but is better tolerated by some patients and is a reasonable option for mild-to-moderate cases.
Weight loss — through diet, exercise, or bariatric surgery — can significantly reduce OSA severity and in some cases resolve it entirely.
Positional therapy helps patients who experience apnea predominantly when sleeping on their back; devices or techniques that encourage side-sleeping can reduce events.
Surgery — including procedures to remove excess throat tissue (uvulopalatopharyngoplasty), reposition the jaw, or implant a hypoglossal nerve stimulator — is reserved for patients who cannot tolerate CPAP or have specific anatomical causes amenable to correction.
Sleep apnea is a serious but treatable condition. The main barrier to better outcomes is diagnosis: most people with sleep apnea have never been tested. If chronic fatigue, loud snoring, or witnessed breathing pauses are present, a sleep evaluation is the appropriate next step.