Sleep apnea happens when breathing repeatedly stops and starts during sleep, and its causes range from the physical shape of your airway to how your brain controls breathing muscles. An estimated 84 million adults in the U.S. live with obstructive sleep apnea alone, roughly 32% of adults over age 20. Understanding what drives the condition helps explain why it affects some people and not others, and why it can develop at any stage of life.
How the Airway Collapses in Obstructive Sleep Apnea
The most common form, obstructive sleep apnea (OSA), is a mechanical problem. During sleep, the muscles in the back of your throat relax. For most people, this relaxation is harmless. But if certain structures in the throat are large, heavy, or positioned in a way that crowds the airway, they can collapse inward and block airflow entirely.
Several specific structures play a role. The soft palate, the fleshy tissue at the roof of your mouth, can drape downward. The tonsils, if enlarged, press inward from both sides. The uvula, the small tissue that hangs at the back of your throat, tends to be larger and more swollen in people with OSA, containing less muscle fiber and more fluid-filled tissue than in people who don’t snore. Deeper in the throat, the base of the tongue is the single most influential structure. When it falls backward during sleep, it can seal off the airway like a plug.
Central Sleep Apnea: A Brain Signaling Problem
Central sleep apnea works differently. The airway isn’t physically blocked. Instead, the brainstem, the part of the brain that automatically controls heart rate and breathing, temporarily stops sending signals to the muscles responsible for inhaling. Without those signals, you simply don’t breathe for several seconds at a time.
Conditions that damage or impair the brainstem can trigger this form. Heart failure, stroke, and certain neurological conditions are common culprits. Some people develop central sleep apnea at high altitudes, where lower oxygen levels destabilize the brain’s breathing rhythm. Others experience it as a side effect of opioid pain medications, which suppress the brainstem’s respiratory drive.
Body Weight and Neck Size
Excess body weight is the single largest modifiable risk factor for obstructive sleep apnea. Fat deposits around the upper airway narrow the space available for air to pass through. Fat accumulation in the abdomen also pushes the diaphragm upward, reducing lung volume and making the airway more prone to collapse.
Neck circumference is a practical screening measure. A neck larger than 17 inches in men or 16 inches in women is considered a risk factor. That extra tissue around the neck compresses the airway from the outside, especially when you’re lying on your back and gravity pulls the tissue downward.
Genetics and Facial Structure
If a parent or sibling has obstructive sleep apnea, your risk is about 50% higher than someone without that family history. Part of this is inherited body composition, but a significant piece involves the bones and soft tissues of the face and skull. A naturally recessed jaw, a narrow palate, or a smaller-than-average airway opening are traits you’re born with, and they all reduce the space available for breathing during sleep.
Genes linked to sleep apnea are involved in craniofacial development, inflammation, and how the body stores fat. You can’t change your bone structure, but knowing your family history helps explain why some lean, otherwise healthy people still develop the condition.
Hormones, Sex, and Menopause
OSA affects men at nearly double the rate of women before menopause, with prevalence at about 39% in males versus 26% in females. Hormones explain much of this gap. Estrogen receptors exist directly in the throat muscles that hold the airway open. In animal studies, estrogen stimulation strengthens the genioglossus, the primary muscle controlling the tongue’s position during sleep. Progesterone acts as a respiratory stimulant, boosting breathing drive through the brain’s chemical sensors.
This hormonal protection largely disappears after menopause. As estrogen and progesterone decline, several things shift at once: the soft tissue in the throat becomes more collapsible, respiratory drive decreases, sleep becomes more fragmented with increased arousals, and body fat tends to redistribute toward the neck and abdomen. The combination means postmenopausal women develop sleep apnea at rates that approach those of men the same age.
Thyroid Disease and Other Medical Conditions
An underactive thyroid contributes to sleep apnea through at least three pathways. Hypothyroidism weakens the respiratory muscles, reducing their ability to keep the airway open. It also causes a specific kind of tissue swelling in the throat: deposits of sugar-protein molecules accumulate beneath the lining of the pharynx, physically narrowing the airway. And because low thyroid function slows metabolism, it promotes weight gain, particularly around the neck and abdomen, which compounds the problem further.
Acromegaly, a condition where the body produces excess growth hormone, can enlarge the tongue and other soft tissues in the airway. Type 2 diabetes, polycystic ovary syndrome, and congestive heart failure are also associated with higher rates of sleep apnea, often through overlapping mechanisms of weight gain, fluid retention, and altered breathing control.
Alcohol and Sedatives
Alcohol selectively weakens the muscles of the upper airway. Research from the American Heart Association confirmed that alcohol reduces the tone of the genioglossus, the tongue muscle that prevents the airway from collapsing. This effect is specific to the upper airway rather than a general depression of breathing. Your diaphragm keeps working, but the throat muscles that hold the passage open go slack.
This means even people who don’t have sleep apnea under normal conditions can experience apnea events after drinking. For people who already have the condition, alcohol makes episodes longer and more frequent, and it deepens the drops in blood oxygen that occur with each pause in breathing. Sedative medications, muscle relaxants, and benzodiazepines produce similar effects on airway muscle tone.
Sleep Apnea in Children
The causes look different in kids. While obesity plays a role in some cases, the leading cause of pediatric obstructive sleep apnea is enlarged tonsils and adenoids. These immune tissues sit right at the back of the mouth and nose, and in children whose tonsils and adenoids are larger than average, they can block a substantial portion of the airway.
Children with certain craniofacial conditions, such as Down syndrome or Pierre Robin sequence, are at elevated risk because of structural differences in the jaw and midface that narrow the airway from birth. Unlike adult sleep apnea, which is usually managed with breathing devices or weight loss, pediatric cases are often resolved by surgically removing the tonsils and adenoids.
Sleeping Position and Age
Sleeping on your back lets gravity pull the tongue and soft palate directly backward into the airway. For some people, positional sleep apnea only occurs when they’re face-up, and simply sleeping on their side eliminates most events.
Age independently increases risk. Muscle tone throughout the body declines as you get older, and the airway muscles are no exception. The tissues of the throat also become less elastic, making them more likely to vibrate (causing snoring) or collapse completely (causing apnea). Fat redistribution with aging tends to favor the neck and trunk, adding mechanical pressure on the airway even without significant overall weight gain.