Most of our ordinary fiberglass insulation is a skin and breathing irritant. That is why we wear gloves, long sleeves, a cotton mask and glasses. For a bit more money you can now buy itchless rock wool (Roxal) and even itchless fiberglass. If you are all itchy, pour milk over the affected area, and the itching will stop -- really.
I also showed a nifty utility knife holder that presses the insulation down tight while cutting -- made by Stanley.