I had a 42mm SS Apple Watch when it was first released. I only had it a few weeks. During this time I never recall any sort of rash or irritation. Since then I was Apple watchless until I got a 42mm Space Gray Sport two days ago. Today was the first time I wore it more than an hour at a time. I wore it a out three hours and when I took it off I had a bright red circle on my wrist where the circle on the back of the watch touches my skin. It was itchy too. The watch was definitely not on too tight. I like to wear my watch loose (don't use the heart monitor). I thought maybe it was just from the watch resting in the spot but then the itchiness worried me. And the red mark also did not go away for about 3 hours. My main question would be is there a difference between the back of an Apple Watch (SS) and a Sport Watch (Aluminum)? Meaning, is the circle part on the back different? Or is it SS on the Apple Watch and Aluminum on the Sport? I'm wondering why the Apple Watch didn't irritate me but the Sport did.