Extreme Skin Irritation

That's a light sweat rash. Seriously, I should post pictures of my wife's wrist before she swapped to a nylon strap.

And that's not the worst it got. Some people have problems with silicone trapping sweat, and there are different silicones. After swapping to a nylon strap, it almost completely disappeared.

Easy to see how tight that watch is being worn by the indentations from the charging port etc. I would suggest that it was being worn too tight. 

I have mine tight enough to stay put when not active and then up a notch when being active and only just see indentations and never from the charging port.. No problem with WHR readings.

That was caused by her wrist swelling as it got inflamed. If she loosened it to suit,  wrist OHR went to pot.

And so far with a nylon strap, zero issues with no change in tightness.

For me I need it tight enough to cause some indentations as well, only my skin just seems to cope with it fine. I've always worn watches tight, so I have a natural groove formed in my arm :)

What you can do, is to wash the back of your watch with a humid cloth every day. This mitigate, skin irritation.

It's a contact irritation from sweat and heat. As others have stated, don't wear the watch tight, ensure you clean it daily and swap to the other wrist for sleeping. If you're a sweaty Betty, the odour free anti-perspirant sprayed on your wrist before you wear the watch will help.

Funny, the gremlins again stole some posts here, including mine. Interesting how those little rascals work