My theory ( sory for bad english ): Edd is borning with deformation head and when was little he was operate for reconstruction his missing part of head with steel one. So parents give him a hat for his protection ( bulling ). So ehen Edd take down his had for first time Eddy said jezz luise or somethink like that because he saw a metal on Edd s head and Ed said cool, because Ed like mutation stuff from magazines and movies. Next episode when second time Edd take had offf Eddy said he burn mine eyes, because sun get on Edd s metal pice to Eddy s eyes and then Edd ask if hurt because Edd has on his head this pice of metal and I think Ed showing where soo he scratch his part of head. This I think maybe is logic maybe is wrong. I hope you understand what i want to say. Soo Edd has a little hair on his head. Regards from Slovenia .