Just select the hair, go to parameters - Actors - Adjustments and check if there are Forehaed width, height, etc...and move the sliders 1% by 1% untill it's fixed.
This can also come from the ligthing, just change the lights.
And the last and FIRST thing you should do, is to center the character in the scene, when the character is far from the center of the scene, this problem ALWAYS happen.