For anyone who's ever had to work with fiberglass insulation, the itching sensation it causes to skin can be pretty intense.
While common sense dictates that you wear protective clothing (long sleeved shirts, gloves, long pants, goggles, and a face mask) to prevent the fibers from getting into contact with your skin, another way to keep the itch at bay is by rubbing some baby powder on other exposed areas like wrists or your neck which might not be fully covered up. If you don't have any baby powder handy, corn starch or plain talc powder should work just as well.