Sleep apnea develops when something repeatedly blocks your airway during sleep or when your brain fails to properly signal your breathing muscles. It affects roughly 15 to 32 percent of adults worldwide, and many people have it for years without knowing. The causes range from physical traits you’re born with to weight changes, hormonal shifts, and other medical conditions that develop over time.
Two Types, Two Different Mechanisms
Obstructive sleep apnea, by far the more common form, happens when the muscles in your throat relax too much during sleep. Your tongue and the soft tissue at the back of your throat collapse inward, physically blocking the airway. You stop breathing for seconds at a time, your oxygen drops, and your brain jolts you just awake enough to reopen the airway. This cycle can repeat dozens or even hundreds of times per night.
Central sleep apnea is less common and works differently. Instead of a physical blockage, your brain temporarily stops sending signals to the muscles that control breathing. The brainstem, which regulates heart rate and respiration, essentially miscommunicates. This type is more closely tied to other serious medical conditions than to body structure.
Excess Weight and Neck Size
About two-thirds of people with obstructive sleep apnea are overweight or obese. Extra fat deposits around the neck and throat narrow the airway even before you fall asleep. When the throat muscles relax at night, that already-narrowed space collapses more easily.
A practical marker: neck circumference greater than 17 inches in men or 16 inches in women is a recognized risk factor. In most people, a neck that size reflects excess fat tissue surrounding the airway. This doesn’t mean thinner people can’t develop sleep apnea, but carrying extra weight in the upper body is the single most common driver of the obstructive form.
Jaw Structure and Airway Shape
Some people develop sleep apnea not because of weight but because of the anatomy they were born with. A recessed lower jaw pushes the tongue closer to the back of the throat, leaving less room for air. A narrow palate, a naturally large tongue, or oversized tonsils can all reduce airway space. These structural traits explain why some lean, fit people still end up with significant sleep apnea. If your family members have it, there’s a good chance you share some of these craniofacial features.
How Age and Hormones Play a Role
Sleep apnea becomes more common with age, partly because muscle tone throughout the body decreases over time, including in the throat. The tissues that keep your airway open simply get looser.
For women, menopause marks a notable shift in risk. Before menopause, women develop sleep apnea at much lower rates than men. During and after menopause, that gap narrows considerably. Research from the Mayo Clinic found that severe hot flashes and night sweats in middle-aged women were linked to intermediate or high risk of obstructive sleep apnea. Hormonal changes, particularly the decline in progesterone (which helps maintain airway muscle tone), likely drive this increase. Troublingly, 65 percent of women identified as being at intermediate or high risk in one study still hadn’t been diagnosed two years later, suggesting the condition is significantly underrecognized in women.
Heart Failure and Central Sleep Apnea
Central sleep apnea frequently develops as a secondary condition in people with heart failure. The two largest studies on this topic found that 33 to 40 percent of heart failure patients had central sleep apnea. A weakened heart changes blood flow and chemical signaling in ways that disrupt the brainstem’s breathing controls. Stroke, kidney disease, and the use of certain pain medications can also trigger central sleep apnea by interfering with the brain’s respiratory signals.
Why Children Get Sleep Apnea
In children, the primary cause is different from adults. Enlarged tonsils and adenoids are the main risk factor, especially in younger kids. These two pads of tissue (tonsils at the back of the mouth, adenoids behind the nose) can grow large enough to physically block the airway during sleep. While childhood obesity can contribute, most pediatric cases trace back to this tissue overgrowth. Surgical removal of the tonsils and adenoids resolves the problem in the majority of affected children.
Sleep Position Matters More Than You’d Think
Gravity plays a surprisingly large role. When you sleep on your back, your tongue and soft palate naturally fall toward the back of your throat. A study in the Journal of Clinical Sleep Medicine found that 60 percent of sleep apnea patients had more than double the breathing interruptions when sleeping on their back compared to their side. This positional effect was actually more significant than the sleep stage (light sleep vs. deep sleep) in determining how severe someone’s apnea was on a given night.
This is why some people with mild apnea can improve substantially just by switching to side sleeping. It’s also why a sleep study done mostly on your back might show worse results than one where you happened to sleep on your side, potentially leading to underestimation of the problem by 20 to 40 percent.
Other Contributing Factors
- Alcohol and sedatives: Both relax the throat muscles beyond their normal resting state, making collapse more likely. Even people without sleep apnea can experience apnea events after heavy drinking.
- Smoking: Chronic irritation increases inflammation and fluid retention in the upper airway, narrowing the passage.
- Nasal congestion: Chronic allergies, a deviated septum, or sinus problems force mouth breathing, which changes airway dynamics and increases the likelihood of obstruction.
- Family history: Inherited features like jaw shape, airway size, and body fat distribution patterns all cluster in families. Having a first-degree relative with sleep apnea raises your own risk.
How Severity Is Measured
Sleep apnea severity is graded by the number of times per hour your breathing stops or significantly decreases during sleep. Fewer than 5 events per hour is considered normal. Between 5 and 15 is mild, 15 to 30 is moderate, and 30 or more is severe. Someone with severe sleep apnea is waking partially, at minimum, every two minutes throughout the night. Many people who assume they “sleep fine” are surprised to learn their number is in the moderate or severe range, because they rarely remember these brief arousals.
Most causes of sleep apnea don’t appear overnight. They develop gradually through weight gain, aging, hormonal changes, or the slow progression of another condition. That gradual onset is exactly why so many cases go undiagnosed for years. The symptoms, chronic fatigue, morning headaches, irritability, feel normal because they crept in so slowly.