I upgraded from an S8 to a U2 on launch and have been wearing it since. I recently noticed a red area on my wrist directly under the sensors. It doesn’t hurt, burn, or itch. My skin isn’t raised and feels normal to the touch. If you look closely the skin is “scaley” (and red, of course). Anybody else notice this?
Just be a little more mindful of the sweat (and therefore bacteria) that builds up under your watch as this is a common symptom.
Something I do is when washing hands with soap I always go under the watch to wipe that part of my wrist.