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Apple Watch has tattoo trouble, Apple confirms

Got a tattoo on your wrist? You could find it difficult to get an Apple Watch to track your heart rate. It's all about the way the ink blocks light from built-in sensors.

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The Apple Watch and tattoos don't play well together, Apple has confirmed. James Martin/CNET

If you have tattoos, you may have one less feature to count on in the Apple Watch.

Apple has updated a support page on its website to say that some people who have tattoos may find that the wearable's heart rate monitoring doesn't work as expected, confirming user reports over the last week who reported errors in the device's readings.

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

This is the first time the company has acknowledged the Apple Watch's issue with tattoos. Over the last week -- the first seven days that the device has been available to consumers -- users who have tattoo "sleeves" have reported that the heart rate monitoring feature would stop working entirely. Until the update, which was spotted today, Apple hadn't said anything about the issue.

The Apple Watch, which requires an iPhone 5 or later to run basic apps and receive notifications, is Apple's first foray into the wearables space, and a pricey one at that. It tops out at $17,000 for the 18-karat gold edition, with more modestly priced options like Apple Watch Sport, which starts at $349.

The smartwatch market had been ticking quietly for several years, with occasional flutters on rumors of an impending watch from Apple. The company first unveiled the Apple Watch in September of last year, and it went on sale last Friday. Analysts have contended that it is the spark that the market has been waiting for.

Competitors include a range of new or updated smartwatches from companies including Sony, Samsung, Huawei, Motorola, LG and Pebble. The Apple Watch's health-tracking capabilities also mean that consumers will be weighing it against fitness bands from the likes of Fitbit and Microsoft.

Unlike with iPhone launches, Apple has not yet disclosed initial sales figures.The smartwatch has been backordered since presales started April 10, and many would-be buyers won't receive their Apple Watches until June or even July. It's unclear how much of the delay is due to the strength of the demand and how much is because of supply shortages and manufacturing issues.

The trouble with tattoos

In order to measure a person's heart rate, Apple Watch has a sensor built into its underside that sits directly above the top of the wrist. When users are looking for their heart rate, the sensor beams green-colored and infrared LEDs at the wrist. That sensor, which flashes the lights hundreds of times per second, uses green light because blood absorbs that color and reflects red. Each time the heart beats, blood flows through the wrist and the light is absorbed. If the heart rate is off beat, the green light absorption is lesser. By measuring light absorption with the sensor, Apple Watch can therefore determine a person's heart rate.

The issue with tattoos, though, is that light is absorbed differently due to the ink. That can limit the accuracy of the heart rate monitor and cause measurements to be off.

Heart rate monitoring can be an important feature for Apple Watch owners. Active users, like runners, often use the feature to see how their heart is faring on a long run. Others may track heart rate to measure stress and overall health.

Apple says that a possible solution to the issue is to use an external heart rate monitor, though that defeats the purpose of having the feature in the first place. It's unclear whether the company will provide any updates to the sensor as time goes on.

Before then, however, Apple may need to worry more simply about getting its watch into consumers' hands.

Apple did not immediately respond to a request for comment.

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