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Hibiscrub is really good for this. Cleaning the rubber and plastic and skin. I dilute it 1/20 wipe and air dry the plastic and rubber and wipe and rinse skin after 5ish mins with water. Also good for groin and gooch based irritation. It kills everything bacteria, fungus and yeast but safe on skin if diluted enough. I used to get 2 sore stripes on my top ribs from my old hr strap.
I have an odd rash under mine on and off. Right now it's not that bad, will try and get a photo of it next time it is a bit scaly there. I wear my 945 pretty much 24/7 and I use the watch for swimming and running. I'm not as hairy as that photo though - I have finer and lighter hair on my arms, mostly because I burned most of it off working in catering 25 years ago.
Generally it's only smelly if I don't clean it well enough. Well enough for me is taking it off at least twice a day and cleaning the wrist area well (with soap) and also giving the back of the watch a good clean to get rid of any salt build up and any skin cells that will accumulate if you don't clean there.
I have a Dettol branded anti-bacterial soap bar in the bathroom.
tl;dr clean the wrist AND the back of the watch twice a day and there should be no problem. If you do this already then clean it more often or pay more attention to it.