Red mark on wrist from Apple Watch

I seem to have this red mark on my wrist from under my watch. I’ve been wearing Apple Watches for 5 years and have had this for over 2 years. I do high level sport and have never had an issue until the last month or two as I clean it regularly. Anyone know what this is and if anything can be done? I saw someone mention it might be a burn.

I noticed within the first day or two of me having the watch that there was a crack in the watch on the underside but until recently it wasn’t one that broke the outer glass so had no issues with it. Although I think on closer inspection it has now broken the outer glass. I’m not sure how it happened- if my watch isn’t on my wrist it’s on the charger. I was told by Apple I would have to buy a new one if I didn’t want the crack in it but I had only just bought it!