Obstructive sleep apnea occurs when the airway narrows or collapses during sleep, preventing enough oxygen from entering the body. When oxygen levels drop, it can harm the heart, lungs, and overall health.

Researchers identify several major causes of sleep apnea, including structural airway issues and problems with muscle control. These causes often overlap, meaning more than one factor may contribute to the condition. Understanding the underlying cause, or “phenotype,” helps guide the most effective treatment.

Narrow or Collapsible Airway

The most common cause of sleep apnea is a narrowed or collapsible airway. It can be compared to trying to breathe through a blocked straw. While other factors also contribute, airway size and structure often play a central role.

Factors that can narrow or collapse the airway include:

  • Fat deposits in the neck pressing on the airway

  • An enlarged tongue that blocks airflow during sleep

  • Excess abdominal fat increasing pressure on the upper airway

  • Small jaw or smaller facial structures

  • Longer airway length, more common in tall individuals or those with long necks

Impairment in Muscle Control

Muscles called pharyngeal dilator muscles normally keep the airway open. If these muscles do not function properly, sleep apnea symptoms may appear. Problems can include weak muscle strength, reduced responsiveness to brain signals, or changes in how the brain controls muscle function over time.

Low Respiratory Arousal Threshold

Some people are naturally “light sleepers.” This trait is known as having a low arousal threshold. People with this characteristic wake up more easily and more frequently at night. For those with sleep apnea, this can worsen breathing disruptions and lead to poor-quality rest, leaving them tired and unrefreshed during the day.

Respiratory Control Instability

Breathing is usually automatic, guided by the brain in response to carbon dioxide (CO2) levels in the blood. When CO2 levels rise, the brain signals the body to breathe faster and deeper.

In some people, this system is unstable, meaning their bodies react too strongly or too weakly to CO2 changes. This instability, sometimes referred to as “loop gain,” increases the likelihood of periodic breathing pauses during sleep, which can contribute to sleep apnea.

Is Sleep Apnea Hereditary?

Genetics can influence the risk of sleep apnea in two ways. First, certain genes directly increase susceptibility. Second, inherited traits that contribute to sleep apnea may raise the risk, such as:

  • Amount and distribution of body fat

  • Facial and skull structure

  • Muscle control of the airway

  • Sleep quality and patterns

Although genetic testing for sleep apnea is still being studied, research suggests that having a parent with sleep apnea increases the likelihood of developing snoring or breathing pauses at night.

Who Gets Sleep Apnea?

Some groups are more likely to develop sleep apnea due to biological and lifestyle factors. These include:

  • People assigned male at birth, who face higher risk overall

  • Older adults, as risk increases with age

  • Post-menopausal individuals, with higher rates after menopause

  • People with higher body fat percentages, which alter airway anatomy

Risk Factors

Obesity is considered one of the strongest risk factors, with about half of people who have obesity also living with sleep apnea.

Other contributing risk factors include:

  • Age over 35

  • Body mass index (BMI) of 25 or higher

  • Excessive alcohol intake

Certain medical conditions also raise the risk, including:

  • Diabetes

  • Heart failure

  • High cholesterol (hyperlipidemia)

  • High blood pressure (hypertension)

Managing these health conditions, along with lifestyle improvements, may help lower the likelihood of developing sleep apnea or reduce symptoms in those already diagnosed.