I had to return my Apple Watch because of an allergic reaction and got the Fenix 5s and am allergic to the back of this one too. I have tried all the washing and drying and it makes no difference. Really disappointed. Had fitbits before this and never had a problem, fear I will have to go back to one.
I’m having the same trouble, have had my Garmin 935 for 3 yrs now and something has worn off on the sensor portion as I get an intense 3 point rash that matches the sensor piece in the center. The metal port also bothers me. I have a mild nickel allergy but after wearing this watch 24hrs per day for years I can barely tolerate it for the hour I exercise each day. Very frustrating for me.