What Causes Grey Color Patch On Back Head?

I know someone who has some sort of skin deformity. He has a patch on the lower back of his head that is grey in color, feels like a skin fungus, almost like it is moist to the touch but its not, it sits on top of his skin/the growth is thick and keeps hair from growing on that part of his head. He has not had it looked at but I want to know what it is and if it can be passed on genetically.