I find the buckles on the silicon straps give me allergic dermatitis, but the Titanium band is fine!! I actually wear the titanium band to work and the dermatitis clears up but recurs when I put the silicon strap on.
The same for me with silicone, I use now stainless steel one and that is just perfect. However, this is thread about nickel, I suppose stainless steel usually contains nickel, so the solution would be plastic model for those people.