Obstructive sleep apnea (OSA) is a sleep-related breathing disorder that affects about 32 percent of U.S. adults. With OSA, the throat muscles relax too much during sleep, blocking the airway and making it hard or impossible to breathe.

OSA causes repeated pauses in breathing because the airway is blocked. Many people know that loud snoring or gasping for air can be signs of sleep apnea. However, not every breathing problem during sleep is the same.

OSA doesn’t have different subtypes, but it does involve several kinds of breathing events, which describe how airflow is reduced or stopped during sleep. Knowing about these events can help you better recognize OSA and understand how it’s diagnosed and treated.

Types of Breathing Events

Doctors count breathing events during sleep to determine how severe OSA is. The apnea-hypopnea index (AHI) is a score based on the number of breathing events per hour of sleep.

OSA severity is described as mild, moderate, or severe, based on your AHI score. In the United States, over half of people with OSA have mild sleep apnea, about 30 percent have moderate cases, and 18 percent have severe OSA, according to a 2025 study in the journal Respiratory Medicine.

It’s helpful to know about these breathing events, but only a trained healthcare provider can measure and interpret them using sleep studies and special equipment. Your doctor can explain what your results mean for your health.

1. Apnea

Apnea is when breathing stops completely for at least 10 seconds. With obstructive sleep apnea, your body tries to breathe, but the airway is blocked. These pauses can lower your blood oxygen, stress your body, and cause your brain to briefly wake you up to start breathing.

Other types of sleep apnea include central sleep apnea (CSA), which happens when the brain doesn’t send the right signals to the breathing muscles. CSA is different from OSA, and it isn’t caused by a blocked airway.

2. Hypopnea

During hypopnea, a partial blockage causes shallow breathing, so you get less air with each breath. Technically, hypopnea occurs when airflow drops by at least 30 percent for at least 10 seconds.

For a hypopnea event to count, it must either wake you up (even if you don’t notice) or lower your blood oxygen by at least 3 percent. Some researchers and doctors count it only if there’s a 4 percent drop in oxygen. These details affect how OSA severity is graded.

Hypopnea isn’t as extreme as apnea, but it can cause you to wake up many times at night and feel sleepy during the day.

3. Respiratory Effort-Related Arousal

A respiratory effort-related arousal (RERA) is a brief period of limited breathing. It’s not as severe as apnea or hypopnea, but it can still awaken you as your body works harder to breathe.

The definition of hypopnea changed when the oxygen drop needed to count was lowered from 4 percent to 3 percent. Some breathing problems that used to be called RERAs may now be counted as hypopnea if they cause a 3 percent drop in oxygen.

Symptoms of Obstructive Sleep Apnea

OSA can cause various symptoms. If you share your bed or room with someone, they may notice problems while you’re sleeping. You may also have daytime symptoms as a result of interrupted sleep. OSA symptoms include:

• Snoring loudly
• Gasping for air while sleeping
• Waking up with a dry mouth
• Experiencing morning headaches
• Feeling irritable
• Being drowsy during the day
• Having a short attention span

Snoring is a common symptom, but it’s not the only one — and some people with OSA don’t snore at all. If you suspect you have a sleep disorder, share your concern with your healthcare provider. They can order a sleep study that measures different types of breathing events linked to OSA.

Factors That Affect Breathing

Breathing events can be more harmful when they happen more often or last longer during sleep. According to a 2023 study in Sleep Medicine Reviews, men tend to have longer respiratory events during sleep than women. Other factors linked to a higher risk or greater severity of breathing problems in people with OSA include:

• Having a larger neck circumference
• Being older
• Sleeping on your back
• Using sedatives, including alcohol
• Gaining weight

The risk of OSA is higher for people with a family history of the condition. OSA is also more common in people with certain health conditions, including:

• Congestive heart failure
• Hypertension (high blood pressure)
• Obesity (having a body mass index of 30 or higher)
• Type 2 diabetes

People who smoke also have about triple the risk of OSA compared with people who don’t smoke.

An OSA breathing event triggers the brain to wake up. These frequent awakenings throughout the night keep you from reaching the deeper, more restorative stages of sleep.

Over time, untreated OSA can lower your quality of life and harm your overall health. Excessive daytime sleepiness can make driving dangerous and make it harder to perform your job or keep up with daily responsibilities. If you sleep with a partner, your disrupted breathing can disturb their sleep, too.

If you think you may have symptoms of sleep apnea, talk with a doctor. Don’t try to judge severity on your own or ignore your symptoms. Treatments are available to help.

Treatments To Help Prevent OSA Complications

Untreated OSA can contribute to serious medical conditions. People with OSA may develop high blood pressure or heart failure (when the heart doesn’t pump as well as it should). They may also have trouble concentrating or experience fatigue during the day.

The good news is there are many treatment options. Sometimes, simple lifestyle changes — like adjusting your sleeping position, quitting smoking, or reducing alcohol use — can make a difference.

A device called a continuous positive airway pressure (CPAP) machine can be worn at night to help treat OSA. The device delivers air pressure through a mask that helps keep the airways open, preventing breathing events and improving blood oxygen levels. CPAP masks come in different styles, and you may need to try more than one to find the right fit.

Your dentist can also prescribe oral appliances (to help move your jaw forward and keep your throat open). These mouthpieces may be less reliable than CPAP, but they can be more comfortable and easier to use, and they may be a good option for people with mild sleep apnea.

Surgery is another option for OSA, usually considered if other treatments haven’t worked. Some people may need to have their tonsils or adenoids removed or have tissue in the back of the throat reduced or repositioned. A newer surgical approach uses an implanted device, similar to a pacemaker, to help keep your airway open during sleep.

With the right diagnosis, you and your sleep specialist can decide which treatment is best for you.

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