Apple aficionados who are also fans of body art are finding out that dark tattoos can daunt the iconic company's hot new smartwatch.

An online Apple support page on Thursday warned that "ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings."

Sensors on the back of Apple Watch wrist wear use LED light to detect blood flow and track heart rates of wearers to provide information such as calories burned or workout intensity.

After release of the Apple Watch on April 24, some users went online with tales of the gadgets acting oddly when adorning tattooed wrists. Applications misfired or stopped working when Apple Watch heart rate sensors had trouble with darkly tattooed skin, some users lamented.

"Many factors can affect the performance of the Apple Watch heart rate sensor," the California firm said on a support page.

Those factors included how much blood flows through a person's skin as well as whether movements are rhythmic, as when running, or irregular, as when playing tennis, according to Apple.

"Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance," Apple said.