Blood oxygen levels and PPG

Your smartwatch measures your heart rate and blood oxygen using light. But what is often overlooked is the effect of skin tone, tattoos, and motion, which can lead to measurement errors.

Regarding heart rate, the studies are unclear about whether skin tone systematically affects the reading. For most users, motion and device fit matter more than pigmentation.

However, blood oxygen is a different story. The same light-based principle used on your wrist is also used in fingertip pulse oximeters that clinicians rely on to decide who gets supplemental oxygen. And there, the evidence is clear: pulse oximeters overestimate oxygen saturation in patients with darker skin, more often miss low oxygen saturation, and delay treatment.

Where is the field going?

A research group at Google published a study showing that video-based resting heart rate monitoring had error rates under the industry accuracy threshold across all three skin-tone groups tested. The FDA published draft guidance in January 2025 recommending skin-tone equity testing for medical pulse oximeters. Recently, Medtronic received FDA clearance for the Nellcor Nell-EQ pulse oximetry system, which was designed to reduce disparities across skin tones.

For wellness, consumer wearables are good for observing trends. But when it comes to influencing healthcare decisions, the bar is higher, and the field needs more work.