Earlier this week, we told you how tattooed iFans on various social media platforms were complaining that certain Apple Watch functions, including Apple Pay and the heart-monitoring and other fitness apps, didn't seem to work properly if the underside of their Watches came in contact with tattooed skin.
Upon inspection, those claims seemed to pan out. Apple's own support page said that certain Watch functions, including the heart rate monitor, use a combination of infrared or LED light pulses and light-sensitive photodiodes to basically shine light through your skin and veins, then measure how much of the light bounces back, and how long that takes.
And when an Apple fan blog tested the Watch's sensors against tattooed and non-tattooed sections of the same person's skin, the results seemed to confirm that yes, tattoo ink does interfere with those light sensors, and the darker or denser the tattoo, the more interference there'd be.
Today Apple confirmed those rumors with an update to its support page titled “Your heart rate. What it means, and where on Apple Watch you'll find it.”
After explaining how its sensors use light to work, Apple asks the question “What else affects your reading?” followed by several paragraphs including these two:
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.
If you’re not able to get a consistent reading because of any of these factors, you can connect your Apple Watch wirelessly to external heart rate monitors such as Bluetooth chest straps.
If you'd rather not bother with that, you should hurry to take advantage of Apple's two-week return window.
There probably isn't any way for Apple to fix this particular problem, short of abandoning light-based sensors altogether. Nothing Apple or anyone else can do will change certain fundamental facts of nature, such as “Crushed minerals and other tattoo-ink ingredients packed together densely enough to look black in full daylight will block or absorb far more light than ordinary human skin and blood ever could.”