Normal blood oxygen levels for healthy adults are between 95% and 100%.

Hypoxemia symptoms include shortness of breath, fatigue, and bluish-colored skin.

Respiratory infections, lung disease, heart disease, anemia, exercise, and altitude changes can affect your blood oxygen levels.

Your blood oxygen level, or oxygen saturation (Sp02), refers to how much oxygen you have in your blood. When you breathe, oxygen moves into your lungs and binds to hemoglobin, a protein in your red blood cells. In your bloodstream, hemoglobin carries oxygen from your lungs to your body's cells, which use oxygen as fuel for energy production. Healthy blood oxygen levels ensure your body's tissues and organs function as they should.

Generally, 92% or more of your blood should carry oxygen to keep your body running smoothly. Most healthy adults have oxygen saturation levels between 95% and 100%, though people with lung problems or those who live at high altitudes (where there is less oxygen in the air) may have lower levels. Prolonged or repeated periods of low blood oxygen levels (hypoxemia) can lead to low oxygen levels in your tissues (hypoxia), which can strain or damage your body's vital organs, including your brain and heart.

Regularly measuring your blood oxygen levels can help monitor how well your lungs are functioning, which can be a helpful way to manage chronic lung conditions, such as chronic obstructive pulmonary disease (COPD). There are two ways to measure blood oxygen levels: pulse oximetry and blood gas tests. 

Pulse oximetry is a non-invasive method for measuring blood oxygen levels at home and in healthcare settings (e.g., doctor's offices, hospitals). A pulse oximeter is a small device that clips onto your fingertip, earlobe, or other body part (e.g., nose, toe) and sends infrared and red light through your soft tissues (e.g., skin, nails) and blood.

A sensor attached to the pulse oximeter clip measures how much light passes through the tissues and blood and how much is absorbed. Oxygenated blood absorbs more infrared light, and deoxygenated blood absorbs more red light.

If you have a chronic lung or heart condition, your healthcare provider may prescribe a pulse oximeter so you can measure your blood oxygen levels at home. Here's how to use a pulse oximeter and ensure you get an accurate reading:

Many pulse oximeters, including wearable devices (e.g., watches), are available over the counter. While these devices may estimate your blood oxygen levels, they are not regulated by the Food and Drug Administration (FDA), may provide inaccurate readings, and should not replace medical pulse oximeters.

An arterial blood gas (ABG) test involves taking a blood sample from an artery in your wrist, arm, or groin. ABG test results show how well your lungs move oxygen and carbon dioxide in and out of your body, including:

Oxygen saturation (02Sat): How much oxygen your red blood cells carry (blood oxygen levels)

Partial pressure of oxygen (PaO2): Measures how well your lungs move oxygen to your bloodstream

Partial pressure of carbon dioxide (PaCO2): The amount of oxygen in arterial blood

Acid-base balance (pH): Measures the acidity of your blood

While most blood tests involve taking a blood sample from a vein, this test involves drawing blood from an artery because arteries hold more oxygenated blood than veins. Because the test involves taking blood from an artery, it may be more painful than your standard blood test. Your healthcare provider may apply numbing cream to your skin before inserting the needle to help reduce discomfort. 

Blood oxygen levels give insight into how effectively your lungs bring in oxygen and how effectively your body absorbs and transports oxygen to your organs and tissues. Normal blood oxygen levels in adults are between 95% and 100% oxygen saturation (pulse oximeter reading).

See a healthcare provider if your at-home blood oxygen measurement is 93% to 94%. Seek emergency care if your blood oxygen levels are 92% or lower.

When measuring your blood oxygen levels at home with a pulse oximeter, several factors can influence your blood oxygen levels and/or the device's measurement, including:

Skin temperature, as having very cold hands may result in an inaccurate reading

Artificial nails and fingernail polish 

Smoking 

High altitude 

Skin pigmentation (pulse oximeters may not give accurate readings on people with darker skin tones)

Skin thickness 

Poor circulation

Hypoxemia is the term for blood oxygen levels that fall below 90% oxygen saturation (SpO2) and 60 millimeters of mercury (mmHg) partial oxygen pressure (PaO2).

While pulse oximeter readings are a reliable measurement of oxygen saturation levels in people with SpO2 of 90% or higher, some research suggests it may be less accurate in moderate or severe hypoxemia cases. For this reason, the severity of hypoxemia is typically determined based on arterial blood gas (ABG) test results, specifically partial pressure of oxygen in arterial blood (PaO2) levels.

Hypoxemia may be mild, moderate, or severe, depending on your PaO2 levels. This is defined by the following ranges:

Mild hypoxemia: PaO2 between 60 to 79 mmHg

Moderate hypoxemia: Between 40 to 59 mmHg

Severe hypoxemia: Lower than 40 mmHg

When your blood oxygen levels fall below the normal range, your cells do not receive enough oxygen to function properly, and you may experience symptoms such as:  

Many factors can influence blood oxygen levels and cause hypoxemia, including conditions that affect lung or heart function, such as:

Environmental and situational factors can also influence blood oxygen levels, including: 

Altitude: Higher altitudes have less oxygen in the air, which can cause hypoxemia, especially in people unacclimatized to high altitudes.

Exercise: Strenuous physical activity increases your body's demand for oxygen; while many people can adapt, those with underlying lung or heart conditions may experience temporary drops in blood oxygen levels.

Smoking: Smoking tobacco damages your lungs and airways and is a significant risk factor for chronic hypoxemia and lung diseases.

Medications: Certain medications, such as opioids and benzodiazepines, can suppress breathing or affect your body's oxygen-carrying capacity.

While occasional, temporary dips in blood oxygen levels are not likely to cause harm, chronically low oxygen saturation or repeated drops can strain or damage vital organs and cause complications, including:

Oxygen therapy is a treatment that provides supplemental oxygen to people with low blood oxygen levels. Healthcare providers can prescribe specific oxygen concentrations (doses) to help boost your blood oxygen levels to within a normal range. Receiving a higher dose of oxygen than you need can lead to hyperoxemia (high blood oxygen levels).

While there is no clear consensus on specific blood oxygen levels for diagnosing hyperoxemia, several research studies suggest thresholds ranging from oxygen saturation levels higher than 96% to 98% and PaO2 levels between 100 and 487 mmHg.

Hyperoxemia symptoms can include:

Sharp chest pains

Heaviness or pressure beneath the sternum (breastbone)

Coughing 

Muscle twitching in the hands

Prolonged hyperoxemia can lead to hyperoxia, or oxygen toxicity. Symptoms of oxygen toxicity include:

The air we breathe contains an oxygen concentration of 21%. Oxygen supplementation in high concentrations can lead to excess oxygen intake and cause hyperoxemia, which can trigger cell damage and death.

Research shows that hyperoxemia can cause lung injury and damage, increase blood pressure, reduce blood flow, and lead to worsened outcomes (e.g., increased risk of mortality) in people receiving oxygen therapy for cardiac arrest, brain aneurysm, and stroke. 

Maintaining optimal blood oxygen levels protects your health and prevents hypoxemia-related complications. Lifestyle modifications and healthy habits that can help manage blood oxygen levels include: 

While occasional fluctuations in blood oxygen levels are normal, persistent drops or concerning symptoms require medical attention. Ignoring low oxygen levels can impact your health and increase the risk of complications, especially if you have a condition affecting lung function.

Make an appointment with your healthcare provider if:

Your oxygen saturation (pulse oximeter reading) is 92% or lower

You have symptoms of hypoxemia, such as shortness of breath, fatigue, chest pain, or headaches

You have a chronic condition (e.g., COPD, sleep apnea, asthma)

Seek immediate medical attention if:

Your oxygen saturation (pulse oximeter reading) is 88% or lower

You experience sudden or worsening symptoms, including rapid breathing, bluish-colored skin, chest pain, or confusion