Tech lovers who have tattoos, take note. Your Apple watch may not track your heart rate perfectly if you wear the sensors over a wrist tattoo.
But even if you have a wrist tattoo, don’t worry, your Apple watch is still one of the best watches for beginners and regular watch wearers alike. There may be a way to get your Apple watch to work for you.
How your Apple watch measures your pulse
Your Apple watch is calibrated to register increasing blood flow through your wrist with each heartbeat. It measures differences in reflection from a green LED light shining on the skin of your wrist.
The way Apple explains the technology, the two green lights on either side of the back of your watch reflect more green light when red blood is pulsing through the arteries in your wrist. (The red lights on the front of the light are there to let you know you have a notification.)
These green lights don’t run all the time. They are more active when your Apple watch detects some reason to measure your pulse rate more often. For example, the green lights will flash more often during a workout.
These lights will shine if you have programmed your watch to track a workout even if you aren’t wearing the watch. They will shut off when your workout is supposed to be finished.
If you find the flashing green lights annoying, you can turn them off. Just open your Apple watch’s privacy settings and go to “Privacy,” and then choose “Health.” This is where you will find the “Heart Rate” feature and have an opportunity to deactivate it. If you want to measure your heart rate again, you have to reactivate the feature. But if you have a wrist tattoo, you may find that your Apple watch is fussy or won’t record your heart rate at all.
The problem with wrist tattoos and your Apple watch
The LED lights on the back of your Apple watch are strong enough that they can illuminate the tiny blood vessels just beneath your skin. Blood absorbs green light, and reflects red light, so the stronger the green light your Apple watch detects from your skin, the less blood is flowing through your wrist.
But your Apple watch does not just attempt to measure your pulse with green light. It also measures your pulse every 10 minutes with infrared light. If it does not get a good reading with infrared light, then it uses green.
Your pulse corresponds with the smallest amount of infrared light or green light your Apple watch can detect. Because your Apple watch sends out hundreds of pulses of light every second, it can measure your pulse to a high degree of accuracy—usually.
Blue ink absorbs both infrared and green light. Black ink absorbs every kind of light, including infrared and blue light. When you have a wrist tattoo done in blue or black ink, your Apple watch registers continuous blood flow. It is as if you have no pulse at all, or no time between pulses, or maybe a very, very rapid pulse. Your watch attempts to compensate by sending out light pulses faster and faster, but usually the result is no reading.
But shouldn’t dark skin interfere with your Apple watch sensor, too?
People who have dark skin don’t have the same problems with Apple watches that people with wrist tattoos do.
That’s because the black, brown, gray, and gold melanin pigments that make skin dark exist in tiny packets called melanocytes. They do not pervade the skin the way tattoo ink does. Nanoparticles of tattoo ink pervade the dermis, the lower layer of the skin, both inside and between skin cells.
If you bruise or sprain your wrist, you may get some irregular readings from your Apple watch. This problem is due to the naturally blue, green, and yellow pigments released from blood inside injured tissues. But you probably wouldn’t want to wear your Apple watch on that wrist, anyway.
Your Apple watch and your wrist tattoos
So, is it possible to get a reliable reading of your heart rate with an Apple watch when you have a wrist tattoo?
The best answer is “Maybe.”
Apple watch users have had extensive discussions about this problem on Reddit and Twitter. They collectively have done very solid, scientifically sensible testing to get to the answer to this problem.
The first thing Twitter and Reddit users tested was whether the problem was the sensors, not the tattoo. They found test subjects who had no wrist tattoos, and tested the Apple watches first on one wrist and then on the other. These readings did not vary, so they concluded that the sensors were working properly, or at least were giving reliable readings.
These citizen scientists also tested the Apple watches on other non-tattooed skin on their test subjects’ bodies, and got the same readings.
Then the informal researchers tested Apple watches on tattooed skin. The watches gave wildly variable pulse readings. Lighter tattoo inks like yellow, orange, and purple resulted in misreadings around 80 beats per minute, when the Apple watch registered 70 beats per minute on non-tattooed skin.
If you have a pattern tattoo, with bare skin between inked sections, you may be able to get a valid reading of your pulse from your Apple watch.
On solid red and solid black tattoos, the Apple watches tested gave readings of over 200 beats per minute before they shut down. That is because the Apple watch can only measure pulse rates between 30 and 210 beats per minute.
So, if I have a wrist tattoo, is there just no way I can use an Apple watch?
If you still aren’t sure how to choose a watch that suits you, consider these facts about your Apple watch.
Apple Watch Series 4, Series 5, Series 6, and Series 7 are designed with electrodes in the digital crown on the back side of the watch. When you place a finger on the digital crown, it forms a closed circuit between both of your arms and your heart. Then you can get a reading of your pulse with the ECG app or the Heart Rate app.
This method comes in handy for trail running. It makes the Apple watch a great choice among watches for doctors. It gives you a more precise reading of your pulse rate than simply wearing your Apple watch on your wrist. Your Apple watch will take your pulse once a second instead of once every five seconds, increasing the accuracy of the reading, regardless of whether you have a wrist tattoo. When you look at recorded data for your Heath App, you will also see your electrocardiogram (EEG) in the “Heart Rate Context” section,
For best results with any Apple watch, you should always start by making sure you have a good fit. You can always try wearing your watch on a non-tattooed wrist, if you have one. Your Apple store has a 14-day return policy, so you could try out an Apple watch for a couple of weeks to see if it works for you.
If you have issues with your Apple watch and still want to use it, you can always turn off Wrist Detection on your Apple watch app to keep it from shutting down. However, turning off Wrist Direction will also shut off Apple Pay, so it may turn out that your best option is wearing your Apple watch over skin that has not been tattooed.