Can skin tone affect wearable heart rate sensors’ accuracy?

Smartwatches and fitness tech like Fitbit wearables and the Apple Watch use a technique known as photoplethysmography (PPG) in which a bright green light shines out of the back of the device and through the wearer’s skin in order to measure their bloodflow. This is how the device measures things like heart rates and sleeping patterns.

Research, however, has determined that “inaccurate PPG heart rate measurements occur up to 15 percent more frequently in dark skin as compared to light skin.” Research has found that melanin, which is a natural skin pigment that has an increased presence in darker skin tones, absorbs the green light from the device before it reaches the blood, which can lead to a 15 percent increase in inaccurate readings. Dark tattoos, sweat and hair can also absorb the light and contribute to inaccuracies.

Fortunately, the companies that make these devices appear to be listening. Garmin and Fitbit, for example, have reportedly configured their devices to boost the intensity of the green light if the device is having trouble detecting a pulse. This allows more light to penetrate the skin, creating more accurate readings. And although it hasn’t mentioned skin tone explicitly, Apple has stated that tattoos can affect the accuracy of the Apple Watch’s readings and that “the optical heart sensor is designed to compensate for low signal levels by increasing both LED brightness and sampling rate.”