I used to work for a firm that distributed glass fibre insulation. We were told to wash in cold, soapey water after handling it. The ends of the microscopic fibre strands pierce and stick into your skin (which makes you itch). The cold water makes the strands brittle and they then break off in the washing process, the bits in your skin just fall out or grow out as your skin grows and sheds. I didn't believe them at first but after fibreglassing a loft, tried the cold shower routine and it worked a treat. The secret is to wear gloves, goggles and full body coveralls in the first place!
(not in the shower - Doh!)