Sleep apnea happens when breathing repeatedly stops and restarts during sleep, and the causes range from physical anatomy to hormones to lifestyle habits. Most cases are obstructive sleep apnea (OSA), where the airway physically collapses during sleep. A smaller number involve central sleep apnea, where the brain temporarily stops sending breathing signals to the muscles. Understanding what’s behind your specific case matters because many of these causes are treatable or manageable.
How the Airway Collapses
During sleep, the muscles supporting soft tissues in your throat relax. This includes muscles attached to your tongue, the soft palate at the back of your mouth, and the side walls of your throat. In most people, these muscles relax just enough to keep the airway open. In people with OSA, the airway narrows or closes entirely, cutting off breathing for seconds at a time.
Whether your airway collapses comes down to a balance between two forces: the pressure of surrounding tissue pushing inward and the strength of muscles holding the airway open. Anything that tips that balance, either by adding bulk around the airway or weakening those muscles, can trigger apnea events.
Excess Weight and Neck Size
Obesity is the single most common contributor to obstructive sleep apnea in adults. Fat deposits along the lateral walls of the throat physically narrow the airway and make it more collapsible. It’s not just about the fat pads themselves. Increased thickness in the pharyngeal muscle wall plays an even larger role than the fat surrounding it. On top of that, abdominal fat reduces lung volume, which decreases the tension holding the airway open from below, making collapse more likely.
The muscles responsible for keeping your airway open also work less effectively when you carry extra weight. They fatigue more quickly and generate less force, which means they’re less able to counteract the inward pressure while you sleep.
Neck circumference is one of the most practical indicators of risk. A neck larger than 17 inches in men or 16 inches in women is a recognized risk factor. This measurement captures the amount of tissue surrounding the airway better than body weight alone, which is why some people at a normal BMI still develop sleep apnea if they carry weight in the neck and jaw area.
Anatomy You’re Born With
Some people have airways that are naturally narrower due to the shape of their jaw, the size of their tongue, or the position of their soft palate. A recessed or small lower jaw pushes the base of the tongue backward into the throat, reducing the space air has to flow through. These structural traits run in families. Overall, first-degree relatives of someone with OSA have about a 50% greater risk of developing it compared to the general population.
Enlarged tonsils and adenoids are another major anatomical cause, particularly in children. In adults, the main risk factors are obesity and age. In kids, oversized tonsils in the back of the mouth and enlarged adenoids behind the nose are the primary culprits. This is why childhood sleep apnea often resolves after surgical removal, while adult cases typically require ongoing management.
Age, Sex, and Hormonal Shifts
Sleep apnea becomes dramatically more common with age, and the increase is especially sharp for women after menopause. Between ages 30 and 49, OSA affects roughly 27% of men and 9% of women. After age 50, those numbers jump to 43% and 28%, respectively. That’s a more than 200% increase in prevalence for women, compared to about 60% for men. The hormones estrogen and progesterone appear to protect the airway by maintaining muscle tone and influencing fat distribution. As those hormone levels drop during menopause, women lose that protective effect and their risk climbs steeply.
Hormonal and Endocrine Disorders
Several hormone-related conditions can cause or worsen sleep apnea through mechanisms that go beyond simple weight gain.
Hypothyroidism (an underactive thyroid) narrows the airway through a process distinct from fat deposition. The soft tissues of the throat become infiltrated with proteins and mucopolysaccharides, a type of swelling characteristic of severe hypothyroidism. Nerve damage from the condition can also impair the muscles that hold the airway open. In some cases, an enlarged thyroid gland itself presses on the airway.
Acromegaly, a condition caused by excess growth hormone, changes both bone and soft tissue in ways that promote airway collapse. The lower jaw rotates and shifts, pushing the tongue base backward and narrowing the space behind the throat. Meanwhile, soft tissues throughout the airway thicken due to increased collagen production and fluid retention. Growth hormone also weakens the pharyngeal dilator muscles, the very muscles responsible for keeping the airway from collapsing during sleep.
Alcohol, Sedatives, and Smoking
Alcohol is a central nervous system depressant that also relaxes muscles throughout the body. During sleep, it specifically reduces the activity of the genioglossus, the main muscle that keeps the tongue from falling backward into the throat. Even moderate drinking in the evening can worsen apnea severity in someone who already has the condition, and it can trigger events in people who otherwise wouldn’t have them.
Sedative medications work through a similar mechanism, suppressing the brain’s ability to maintain airway muscle tone during sleep. The combination of alcohol and sedatives compounds the effect.
Smoking contributes through a different pathway. It triggers inflammation in the upper airway, causing swelling that narrows the passage. Smoking also appears to disrupt normal sleep architecture and impair the neuromuscular function of the upper airway muscles, making them less responsive to the signals that would normally keep the airway open.
Sleep Position
Sleeping on your back roughly doubles the frequency of breathing interruptions compared to sleeping on your side, to the point that “positional OSA” is its own recognized subtype. Gravity pulls the tongue and soft palate backward when you’re face-up, and the effect is significant enough that some people only experience apnea in the supine position. For these individuals, simply switching to side sleeping can dramatically reduce or even eliminate events.
Central Sleep Apnea: A Brain Signal Problem
Central sleep apnea is fundamentally different from the obstructive type. The airway doesn’t collapse. Instead, the brainstem temporarily stops sending the signals that tell your breathing muscles to contract. This form is less common but tends to occur alongside serious medical conditions.
Congestive heart failure is the most frequent underlying cause, often producing a distinctive pattern called Cheyne-Stokes breathing, where breathing gradually deepens, then shallows, then stops entirely in a repeating cycle. Stroke is another common trigger, particularly when it damages the brainstem, the region that controls heart rate and respiration. Sleeping at high altitude can also cause central apnea because lower oxygen levels disrupt the brain’s normal breathing regulation.
Sleep Apnea in Children
Pediatric sleep apnea deserves its own mention because it looks and acts differently from the adult version. While adults typically present with daytime sleepiness, children are more likely to show behavioral changes: hyperactivity, difficulty paying attention, or acting out. Parents often don’t connect these symptoms to a sleep problem.
The dominant cause in children is enlarged tonsils and adenoids. Obesity can contribute, but it plays a secondary role compared to adults. Children born with differences in the shape of their face or head, such as those associated with Down syndrome or Pierre Robin sequence, also face elevated risk. Because the primary cause in kids is structural, treatment is often more straightforward. Removing the tonsils and adenoids resolves the condition in a large number of pediatric cases.