It's normal for blood oxygen levels to fluctuate slightly during sleep, but significant drops may be a sign of something more serious, like sleep apnea. For most people, a normal level of blood oxygen is between 95% to 100%. When levels fall below this range—especially repeatedly or for extended periods—it could indicate disrupted breathing and a need for further medical evaluation.
What Happens to Blood Oxygen During Sleep
During sleep, a person’s respiratory rate (breaths per minute) naturally becomes less consistent and shifts as they move through the different stages of sleep. It’s normal for a sleeper to have periods of slow or shallow breathing and short pauses in breaths. While normal, these changes in breathing can cause a sleeper’s blood oxygen levels to temporarily decrease.
While minor changes in blood oxygen levels are expected during sleep, a wide range of health problems can cause oxygen levels to drop too low. Tissues in the body need oxygen to stay healthy, so a blood oxygen level that's too low can be dangerous to a person’s health.
Measuring Blood Oxygen During Sleep
Blood oxygen levels can be measured through a blood test or by using a medical device called a pulse oximeter. A pulse oximeter is a small device that is typically clipped on a finger and provides an estimate of the level of oxygen in the blood.
Over-the-counter pulse oximeters and smartphone-based devices have also been developed to check a person’s blood oxygen level at home and became increasingly popular during the COVID-19 pandemic. However, experts warn that these non-prescription products haven’t been thoroughly tested and shouldn’t be used to monitor a person’s health.
For most people, there's no need to measure oxygen levels during sleep. In situations when a doctor does recommend using a pulse oximeter at home, such as in those with lung disease or COVID-19, the doctor can provide a prescription for an FDA-cleared pulse oximeter.
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Normal and Dangerous Blood Oxygen Levels During Sleep
Normal blood oxygen levels vary from person to person, but for most it’s around 95% to 100% regardless of whether they are asleep or awake. A blood oxygen level below 92% may be a cause for concern, while a level below 88% requires prompt medical attention.
| Blood Oxygen Level | Interpretation |
|---|---|
| 95 to 100% | Normal range |
| 91 to 95% | Borderline low |
| 88 to 91% | Low |
| Lower than 88% | Dangerously low |
While these estimates of normal and potentially dangerous blood oxygen levels can be helpful, there are a number of other factors that doctors take into account when assessing the meaning of a person’s blood oxygen levels.
- Previous readings: Doctors often look at trends in a person’s blood oxygen level rather than a single measurement. For example, even an oxygen level of 95% could be a cause for concern in a person who previously had a blood oxygen level of 98%.
- Elevation: High elevations can cause a person’s blood oxygen to be lower than it would be at sea level.
- Pre-existing health conditions: Blood oxygen levels may also be lower in people who have been diagnosed with health issues that affect the lungs, like chronic obstructive pulmonary disorder (COPD) or pneumonia.
- Device margin of error: Pulse oximeters provide only estimates of blood oxygen and readings can be several percentage points different than a person’s actual level.
For these reasons, only a doctor can determine if a person’s blood oxygen is dangerously low.
Signs of Low Oxygen Levels While Sleeping
Low blood oxygen during sleep can be hard to detect without monitoring equipment, but there are common signs and symptoms that may suggest your body isn’t getting enough oxygen at night. These symptoms often overlap with sleep disorders like obstructive sleep apnea and can affect both your nighttime rest and daytime functioning. Common signs include:
- Loud or frequent snoring
- Gasping, choking, or snorting during sleep
- Restless or fragmented sleep
- Waking up with a dry mouth or headache
- Excessive daytime sleepiness or fatigue
- Difficulty concentrating or memory issues
- Mood changes, such as irritability or depression
- Shortness of breath when waking up
If you or a loved one regularly experiences these symptoms, it may be worth speaking with a healthcare provider about a sleep study or overnight oxygen monitoring.
Reasons for Low Oxygen Levels While Sleeping
Oxygen is taken into the body through the lungs and circulated in the bloodstream. It's then used by tissues in the body to create energy. Changes or problems at any point in this process can cause a decrease in a person’s blood oxygen level.
A wide range of medical conditions can cause a person’s oxygen levels to decrease during sleep, including:
- Obstructive sleep apnea (OSA): OSA is a condition where the airway becomes repeatedly blocked during sleep, leading to breathing pauses and oxygen levels drops.
- Central sleep apnea (CSA): CSA is a less common form of apnea where the brain doesn’t consistently signal the body to breathe.
- Chronic obstructive pulmonary disease (COPD): Lung conditions like emphysema or chronic bronchitis can limit airflow and oxygen exchange, especially at night.
- Asthma: Poorly controlled asthma can cause nighttime airway constriction and reduced oxygen levels.
- Sleep-related hypoventilation: This is a condition where breathing is inadequate during sleep, either too shallow or too slow.
- Obesity hypoventilation syndrome (OHS): Excess weight can affect how the lungs and chest muscles function during sleep.
If it's none of the above, a doctor may diagnose a person with sleep-related hypoxemia, a sleep disorder in which nighttime drops in blood oxygen can’t be attributed to other sleep-related breathing conditions. Most often, sleep-related hypoxemia is caused by an underlying medical condition. These conditions include:
- Lung disease
- High blood pressure
- Conditions that affect the nerves and muscles
- Flare ups of respiratory conditions
How to Increase Oxygen Levels While Sleeping
People who are concerned about their blood oxygen levels during sleep should contact their doctor, as only a healthcare provider can assess changes in blood oxygen levels and recommend appropriate treatment.
When treatment for low blood oxygen is necessary, treatment depends on the cause of the condition. For example, people with obstructive sleep apnea may be prescribed a continuous positive airway pressure (CPAP) device, while those with sleep-related hypoxemia may be prescribed supplemental oxygen to use while they sleep.
Additionally, there are several lifestyle changes you can make to promote better oxygen intake and circulation while sleeping.
- Sleep on your side: Sleeping on your back can worsen airway obstruction in some people. Side sleeping may reduce breathing pauses and improve airflow.
- Keep your sleeping area allergen-free: Dust, pet dander, and mold can worsen breathing at night. Use hypoallergenic bedding and clean your bedroom regularly.
- Use a humidifier: Moist air can ease breathing by preventing dry nasal passages and airways.
- Maintain a healthy weight: Excess weight, especially around the neck and chest, can make breathing more difficult during sleep.
- Practice good sleep posture: Elevating your head slightly with a supportive pillow may help reduce airway compression.
- Avoid alcohol and sedatives before bed: These substances can relax throat muscles, increasing the likelihood of airway collapse and oxygen dips.
When to See a Doctor
People concerned about their blood oxygen level should discuss their concern with a doctor, particularly if they're experiencing other symptoms of insufficient oxygen, such as:
- A cough that gets worse over time
- Rapid heartbeat
- Discomfort, tightness, or pain in the chest
- Lips, face, or nails that develop a blue tint
- Difficulty breathing or shortness of breath
Additionally, if you regularly feel exhausted despite a full night’s sleep, snore loudly, gasp for air at night, or wake up with headaches or shortness of breath, it’s important to talk to your doctor. You should also seek medical advice if:
- You’ve been told you stop breathing or gasp during sleep
- You have a chronic lung or heart condition and are experiencing new or worsening symptoms
- You’ve used a pulse oximeter and consistently see readings below 90% during sleep
A healthcare provider may recommend a sleep study, overnight oxygen monitoring, or other tests to determine the cause and guide you toward the most effective treatment.
Written by
Rob Newsom, Staff WriterRob writes about the intersection of sleep and mental health and previously worked at the National Cancer Institute.
Reviewed by
Gerard Meskill, MD, FAASM, Medical ReviewerGerard J. Meskill, MD, is board certified in both neurology and sleep medicine, and he is the founder and CEO of Tricoastal Narcolepsy and Sleep Disorders Center. The “Tricoastal” moniker references his background: he completed neurology residency on the East Coast at Long Island Jewish Medical Center – where he served as chief resident, sleep fellowship on the West Coast at Stanford University, and he now practices sleep medicine and neurology on the Gulf Coast in the greater Houston, Texas area.
