There are issues with raw egg white and the absortion of some vitamins. Avidin is a glycoprotein, which is found in raw egg whites, and blocks the uptake of Vitamin B6 and Vitamin H (Biotin) causing a vitamin deficiency (it binds to Biotin and iron making them unavailable). You must cook/pasteurize the egg white to neutralize the Avidin and allow your body to safely digest the protein and utilize all its amino acids.

From http://forum.bodybuilding.com/showthread.php?t=540518