Apnea is a temporary pause in breathing. The term comes from Greek, literally meaning “without breath.” While apnea can occur in different medical contexts, it most commonly refers to sleep apnea, a condition where breathing repeatedly stops and starts during sleep. Nearly 1 billion people worldwide are affected, and an estimated 83.7 million adults in the United States alone live with some form of it.
How Apnea Works During Sleep
When you fall asleep, every muscle in your body relaxes, including the muscles in your throat that help keep your airway open. For most people, this relaxation doesn’t cause problems. But in people with sleep apnea, the relaxed muscles combine with a naturally narrower airway to partially or fully block airflow.
A partial blockage that reduces oxygen intake is called hypopnea. A complete pause in breathing is apnea. These events can last anywhere from a few seconds to over a minute, and they can happen dozens or even hundreds of times per night. Each time, your brain briefly wakes you (often without your awareness) to restore normal breathing. The result is fragmented, poor-quality sleep even if you think you slept through the night.
During these pauses, blood oxygen levels drop. Normal oxygen saturation sits around 96 to 97%. Mild drops bring levels down to about 90%, moderate drops land in the 80 to 89% range, and severe drops fall below 80%. These repeated oxygen dips stress the heart and blood vessels over time.
Three Types of Sleep Apnea
Obstructive sleep apnea (OSA) is by far the most common type. It happens when the soft tissue in the back of the throat physically collapses and blocks the airway during sleep. Risk factors include excess weight, a thick neck circumference, and structural features like a small jaw or enlarged tonsils.
Central sleep apnea is different. The airway isn’t blocked. Instead, the brain temporarily fails to send the signal telling your muscles to breathe. This type is less common and often linked to heart failure, stroke, or the use of certain medications, particularly opioids.
Mixed (or complex) sleep apnea is a combination of both. It typically starts as obstructive events but also involves a central component, sometimes only becoming apparent after treatment for the obstructive type begins.
Symptoms You Might Notice
Many people with sleep apnea don’t realize they have it. The breathing pauses happen while you’re asleep, so the first clue often comes from a bed partner who notices loud snoring, gasping, or moments where breathing stops entirely. Snoring is more common in men, though it can affect anyone.
The symptoms you’re more likely to notice yourself include:
- Daytime sleepiness and fatigue that persists even after what seemed like a full night’s sleep
- Morning headaches and dry mouth
- Trouble concentrating, learning, or reacting quickly
- Waking up frequently at night, including to urinate
- Insomnia or restless sleep
- Decreased sex drive
Women tend to report fatigue, headaches, and insomnia more often than the classic loud snoring, which can lead to underdiagnosis. Children with sleep apnea may show hyperactivity, bedwetting, worsening asthma, and difficulty paying attention in school rather than the typical adult symptoms.
Who Gets It
Sleep apnea is far more common than most people assume. A 2024 analysis estimated that about 32% of U.S. adults aged 20 and older have obstructive sleep apnea. The condition affects roughly 39% of men and 26% of women. Of those affected, about 52% have mild cases, 30% moderate, and 18% severe.
Those numbers have climbed dramatically from earlier estimates. Studies from the late 1980s and early 1990s put the prevalence at 6.5 to 9% in women and 17 to 31% in men. Rising obesity rates are a major driver of the increase, since excess weight around the neck and throat is one of the strongest risk factors for airway obstruction during sleep.
How Severity Is Measured
Doctors diagnose sleep apnea using a sleep study, either in a lab or with a home testing device. The key measurement is the apnea-hypopnea index, or AHI, which counts the number of times you stop breathing or have a significant airflow reduction per hour of sleep. An AHI of 5 to 15 is considered mild, 15 to 30 is moderate, and above 30 is severe.
Treatment Options
CPAP Therapy
The first-line treatment for most people is a CPAP machine, which delivers a steady stream of pressurized air through a mask worn during sleep. This air pressure acts as a splint, keeping the airway open. CPAP is remarkably effective. In one study, the average number of breathing disruptions per hour dropped from about 56 to fewer than 3 within the first month of use.
The challenge is sticking with it. CPAP adherence rates range from 30 to 60% depending on the study, and long-term compliance drops further. Only about 45% of patients meet recommended usage thresholds at the one-year mark. Many people struggle with mask discomfort, dry air, noise, or simply find the device inconvenient. Modern machines are quieter and offer features like heated humidifiers and auto-adjusting pressure, which can help.
Oral Appliances
For people with mild to moderate sleep apnea, or those who can’t tolerate CPAP, a mandibular advancement device is another option. This custom-fitted oral appliance looks similar to a sports mouthguard and works by pushing the lower jaw and tongue slightly forward, which opens more space in the airway. A dentist trained in sleep medicine typically fits these devices.
Surgical Approaches
When CPAP and oral appliances aren’t effective, surgery becomes an option. One common procedure moves the upper and lower jaw bones forward, which physically enlarges the airway. Newer techniques have eliminated the need for jaw wiring during recovery and use nerve blocks to reduce pain significantly. Beyond treating the breathing problem, this surgery can improve bite alignment and facial appearance.
A newer category of treatment involves a small implanted device that stimulates the nerve controlling the tongue. When you breathe in during sleep, the device gently moves the tongue forward to prevent airway blockage. This option is generally reserved for people with moderate to severe sleep apnea (an AHI of 15 to 60) and a BMI under 35 who haven’t been able to use CPAP successfully.
What Happens Without Treatment
Untreated sleep apnea does more than ruin your sleep. The repeated drops in oxygen and the stress of constant nighttime awakenings take a toll on the cardiovascular system. The condition is strongly associated with high blood pressure, heart disease, stroke, and irregular heart rhythms. It also raises the risk of type 2 diabetes, worsens depression, and significantly increases the chance of drowsy-driving accidents.
Because many people don’t know their breathing is disrupted at night, sleep apnea often goes undiagnosed for years. If you regularly wake up feeling unrefreshed, experience persistent daytime sleepiness, or have been told you snore loudly, those are signals worth investigating with a sleep evaluation.