Apple admitted tattoos can interfere with Apple Watch heart rate readings, according to numerous media reports including Tech Crunch.

Irked inked Apple Watch users posted videos online last week of how the watch would fail to pick up heart rate readings or even automatically lock down when in contact with tattooed skin.

Apple Watch has been unable to accurately measure heartrates on tattooed skin. (Photo Courtesy of Apple)

Apple has confirmed tattoos can cause issues in the watch performance, and updated its support section to include the following passage:

“Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance. The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings.”

Apple has explained in its previous support document that the watch relies on photoplethysmography technology to acquire heart rate readings. Blood, which is red in color, absorbs green light. The green LEDs in the Apple Watch paired with light-sensitive photodiodes depend on this light absorption mechanism to take accurate heart rate readings.

Ink underneath the skin could obstruct light emission from the LEDs as well as light reflected from the blood vessels, hence preventing the LEDs from picking up accurate readings.

Apple has recommended tattooed users to try connecting the Apple Watch wirelessly to external heart rate monitors, such as Bluetooth chest straps, reported Tech Crunch.