Wearable Tech Struggles With Accuracy On Darker Skin

For the nearly 107 million Americans who wear a fitness tracker or smartwatch, these devices have become essential companions for monitoring daily health. They track steps, workouts, and recovery, offering a constant stream of data about how the body is functioning. However, a growing body of research suggests that this data may not be equally reliable for everyone, raising concerns about who can truly trust the numbers on their wrist.

A 2025 review of smartwatch accuracy studies found significant variability in how devices perform across different skin tones. While some major brands maintained heart rate accuracy within five beats per minute for all users, other devices underestimated heart rates by ten to 15 beats per minute in users with darker skin. This discrepancy is particularly concerning during moderate to vigorous exercise, where precise data is crucial for gauging intensity and recovery.

Optical Sensors Face Physical Limits

Most modern wearables rely on a technology called photoplethysmography, or PPG, to measure blood flow. These devices use optical sensors that shine green light into the skin. Hemoglobin, the protein in blood that carries oxygen, absorbs some of this light, while the rest reflects back to the sensor. The device then measures changes in this reflected light to estimate heart rate.

The trade-off lies in the physics of light absorption. Melanin, the pigment responsible for skin color, also absorbs and scatters the light emitted by the sensor. In skin with higher melanin content, more light is absorbed rather than reflected. This makes it harder for the device to get a clear signal, leading to data loss and reduced accuracy compared to lighter skin tones.

Health Risks From Inaccurate Data

Accurate heart rate readings are more than just a metric for fitness enthusiasts; they can be lifesaving. Irregular heartbeats can indicate serious cardiovascular issues, such as blood clots, stroke, or heart failure. If a device fails to flag these red flags due to technical limitations, users may miss critical warnings that could prompt them to seek medical attention.

The issue is not new to the industry. Companies like Apple, Oura, and WHOOP are aware that getting accurate data from darker skin requires extra engineering effort. As reported by GN auto tech/wearables, manufacturers are now under pressure to ensure their technology is reliable across the full spectrum of human skin tones, rather than just optimizing for a narrow demographic.

Challenges In Classifying Skin Tone

Addressing this bias is complicated by how skin tone is categorized. Dermatologists often use the Fitzpatrick Scale, a six-point system based on how likely a person is to burn or tan. However, recent medical studies note that this scale is flawed because it relies on self-perception and cultural influences, making it an imprecise tool for engineering optical sensors.

Beyond skin tone, other factors like movement noise and sensor placement also affect accuracy. Experts emphasize that while technology improves, users must remain aware of the limitations. Relying solely on a wrist device for medical insight carries a risk, especially if the underlying data is skewed by the physical interaction between light and pigment.