stihl fs 56 causing forearm to break-out (rash on forearm)

hi, I have a fs 56r (I believe that is what it is) with a loop handle that I have used for the last 2-3 years. lately I have been breaking out on my forearm every time I use it. it is where my arm rests against the body of the trimmer while using. my question is ... is the housing made of fiberglass or plastic? thanks in advance for any information on this.

stihl fs 56 causing forearm to break-out (rash on forearm)