SpO2 — Blood Oxygen Saturation and What It Actually Tells You
Normal is 95–100%. What happens below that — and why your wearable data matters more than you think.
Track This Biomarker Free → ← All BiomarkersWhat Is SpO2 — Blood Oxygen Saturation and What It Actually Tells You?
SpO2 measures the percentage of hemoglobin molecules carrying oxygen in the bloodstream. Consumer wearables use photoplethysmography to estimate this via light absorption. Sustained readings below 94% indicate hypoxemia. Nocturnal dips below 88% are diagnostic for obstructive sleep apnea. COVID-19 research established that SpO2 declines are detectable via wearable days before clinical deterioration.
What Causes SpO2 to Change
The most common drivers behind a change in SpO2 are:
- Altitude exposure above 8,000 feet
- Sleep apnea — nocturnal SpO2 dips during breathing cessation
- Respiratory illness — COVID-19, pneumonia, bronchitis
- Anemia — low hemoglobin reduces oxygen-carrying capacity
- Obesity — increases upper airway restriction risk
- Smoking — damages hemoglobin oxygen-binding capacity
How Hunuu Tracks SpO2
Hunuu integrates SpO2 continuous monitoring from Apple Watch Series 6+, Oura Ring Gen 3, Fitbit Sense, and Garmin devices. Nocturnal SpO2 pattern analysis flags sleep apnea risk and respiratory health trends within the Respiratory health pillar.
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