I’m not exactly sure, but I don’t think, that you’d get rashes, besides having an allergy to that specific molecule, but as they are not really easily broken up, they are also not very reactive friendly - at least that’s my interpretation

So, having them block up some stuff is some reasonable concern and we never really know what happens with them inside our body, but I would guess that your rashes come more from the humidity under the wristband and the constant friction of it - at least my arm doesn’t really like that, but to have a heart monitor on my wrist, I need to wear it quite tight.

And could also be an allergy to something else in the wristband

Edit: I’m too tired and should stop writing…