I second SamTherapy's suggestion. I've seen this before with other hair, though, but only in C4D. One other idea is to check the map size on your shadow maps. If it's low (and by looking at the rest of your pic, it doesn't seem low) you'll get weird effects through transparency (looks like dirt/banding). Finally, I'm not familiar with the model itself, but if it's like other hair there will be a material zone called "skull cap" or something. Not only do you need to check that it's transparency is 100%, but you also have to make sure no color has been applied to the skull cap material, other than white. Please somebody speak up if I'm totally off base! Hope this helps, Jack