Study shows how skin color affects pulse oximeter accuracy

Pulse oximeters are widely used in hospitals and clinics to monitor blood oxygen levels. These small, noninvasive devices estimate oxygen saturation (SpO₂) by shining red and infrared light through the skin and measuring how much is absorbed. While convenient and essential for patient care, especially in emergencies, pulse oximeters have come under scrutiny for being less accurate in patients of color. Clinical studies have shown that these devices often overestimate oxygen levels in patients of color, particularly when oxygen levels are low—a condition known as hypoxemia. This discrepancy can lead to delayed or inadequate treatment.

Despite growing awareness of this issue, the exact cause of the bias has remained unclear. A recent study led by researchers at the University of North Carolina and Washington University School of Medicine aimed to address that gap by directly investigating how skin pigmentation affects the way pulse oximeters work. Their work is published in Biophotonics Discovery.

To isolate the effect of skin pigmentation, the researchers used a unique animal model: Hampshire pigs, which naturally have both dark and light patches of skin. This allowed the team to compare measurements from pigmented and nonpigmented areas on the same animal under identical conditions.

The team built custom pulse oximeters and applied them to both skin types. They then gradually reduced the pigs’ oxygen levels from 100 percent to about 70 percent by adjusting the mix of oxygen and nitrogen in the air. At the same time, they collected arterial blood samples to get accurate oxygen saturation levels (SaO₂) for comparison.

The devices recorded how much red and infrared light—the two wavelengths used by pulse oximeters—was absorbed over time. The researchers used advanced signal processing techniques to separate the pulsatile (heartbeat-related) and baseline components of the light signals. They then analyzed how these signals changed with oxygen levels and compared the results between pigmented and nonpigmented skin.

The results were clear: in darker skin, red light was more strongly attenuated prior to interacting with blood. This effect reduces the device’s ability to detect changes in blood oxygen levels, particularly during low-oxygen conditions—where accurate readings are most critical.

This study provides experimental evidence that skin pigmentation can interfere with the accuracy of pulse oximeters by altering how red light interacts with the skin. The findings support previous clinical observations and suggest that the bias is rooted in the physics of light absorption and scattering in pigmented tissue.

The researchers emphasize the need for further studies to confirm these results in humans and to explore ways to improve device accuracy across all skin tones. They also note that future designs should consider how red light is uniquely affected by pigmentation, especially in low-oxygen conditions.

For details, see the original Gold Open Access article, “Characterizing the influence of skin pigmentation on pulse oximetry,” Biophoton. Discovery 2(3), 032506 (2025), doi 10.1117/1.BIOS.2.3.032506.