I'm having that problem with my 6X Pro silicone strap. I now take it off at night to let my skin breath and recover. I don't think it's an allergy but maybe sweat or constant friction. I'm going to try some lotions or eventually try some other strap material. I was switching wrists every day but both my wrists became irritated in certain areas. Where the fenix metal touched was perfectly fine but where the strap touched it kept getting irritated and the skin darkened and started peeling. So annoying. I'm 71 years-old so maybe my skin is just sensitive. Time will tell as I will keep experimenting with different things like tape under the strap. I never had a problem with any Garmin strap before.
My wife has continual problems - but she has hyperkeratosis (basically very fast growing skin) so her pores are always blocked and as a result bacteria can grow quickly. She's had to use antibac constantly but this isn't just restricted to Garmin - every device she's owned has given a similar problem. Do you have any pre-existing skin conditions?
No, I don't have any pre-existing skin condition that I know of. I think maybe the silicone strap is just too rough for my skin. I've worn other watch bands before and they never had any effect on my skin. I always used to wear Casio solar G-Shock watches but those had metal bands and they didn't affect my skin at all. I always thought my skin was tough because I never had any problems with it. As I said, I'm simply going to do some experimentation. I see there is are nylon bands and leather bands for the fenix on Amazon and I may give them a shot if the Garmin silicone band doesn't work out. I could also go with a metal band, so there are lots of options for me.