Apple Watch Ultra tearing my thin skin

Any kind of guard under the Watch will almost certainly block many of its functions and quite probably block even the wrist detection. I would suggest first taking your Watch to an Apple Store or authorized Apple service center to examine it and see if there's a manfacturing defect or damage that has caused a sharp edge or burr.

If not, I'd recommend talking to your doctor who may refer you to a dermatologist with whom you can discuss your situation. Meanwhile, you should of course change the Watch to your other wrist while the injury heals.

Regards.

First please contact your primary care physician and discuss the situation. Then go to a well stocked drug store and buy some moleskin. Cut small pieces of mole skin and fit them along the edge of your Ultra.

Moleskin is usually found in the foot care section it has a soft cushioning surface the reduces the friction that will cause tearing of the skin. Hikers, backpackers and climbers have used moleskin for decades to prevent blisters and to relieve blisters that have developed.

https://www.drscholls.com/products/moleskin-plus-padding-strips

Stop wearing it and talk to your doctor.

... and also let Apple Support know.

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