In the TV show that is called "Smallville," the reason why their Lex Luthor is bald is because of the meteor shower that happened in 1989 which was a masked to hide the arrival of a Kryptonian ship which brought Kal-El (also known as Clark Kent or Superman) to Earth, the meteor shower caused meteors (called Kryptonite) to land on the town of Kansas including in the corn field where a young Lex was at and the meteor caused his hair to fall off and to never be allowed to grow back.
Luthor went bald from a chemical warfare experiment that went awry. He was rescued by Superman, but the hair damage was already done, Had he worn a protective helmet like even a so-called shower helmet, it would not have happened. so the story goes, prior to the accident, Luthor was a promising scientist, after it, a mad scientist of criminal bent. He blamed Superman for his baldness.