Allergic to Office? What are office chair rests made of? Vinyl?

I have been suffering from hives for about three months now that only seem to be a problem in my office.   I have been at the same desk for almost three years with the same chair, but it seems that everytime my bare forearms lay on the armrest that I get hives that travel up my arm, and my fingers on my right hand start to swell.  I also strangely enough get hives on my knees?

I am scheduled to have allergy testing done on June 15th, but I am wondering in the meantime if anyone knows what material the cushy black armrest might be made of?