Some Apple Watch Series 12 and Ultra 4 owners say they have felt burning or noticed redness beneath the sensor area. MacRumors reported the complaints from its forums and Reddit, but the posts do not show how common the problem is or what caused it. Apple has not confirmed a sensor-related issue.
The new sensors are one theory
The Series 12 and Ultra 4 use Apple’s latest Health Sensing System. The Series 12 measures heart rate every five seconds throughout the day. MacRumors also points to larger green LEDs, a larger ECG electrode surface, and photodiodes arranged in a ring. Owners have wondered whether the redesigned sensor has anything to do with the irritation, but no evidence connects those changes to the reports.
The complaints MacRumors reviewed describe symptoms in the same area where the watch rests against the wrist. Some owners said cleaning the back of the watch or changing the fit helped. Others returned their devices. Those experiences do not confirm a common cause, and similar complaints about Apple Watch have appeared before the current generation.
Fit and moisture can irritate skin
Apple’s wearing guidance says skin reactions can relate to allergies or sensitivity to materials, sweat or soap trapped against the skin, and a band that is too tight or too loose. Apple says a small number of people may react to nickel or trace acrylates and methacrylates in some cases, though the latter are designed to stay out of direct skin contact. A tight band can irritate the skin, while a loose one can rub. Apple recommends keeping the watch, band, and skin clean and dry, especially after workouts or contact with liquids such as sweat, soap, sunscreen, or lotion.
That guidance does not explain the new reports. It does show why redness under a watch cannot, by itself, identify a defect in the sensor. The Apple Watch Ultra 4’s health features and other Apple Watch health tools rely on close contact with the wrist, but Apple’s advice also accounts for fit and skin sensitivity.
What owners should do
Apple says people who notice redness, swelling, itchiness, or other irritation should consult a physician before wearing the watch again. Its guidance also recommends checking the fit and cleaning the watch and band, particularly after exercise. Owners in the reports tried some of those steps, but the anecdotes are not enough to show whether they address a sensor problem.
