Baldness

Baldness is a condition that happens to human beings when they lose their head hair, either through the passage of time or by certain conditions that cause it to happen prematurely.

Mainstream Smurfs Media
In mainstream Smurfs media, the male Smurfs are born bald, with head hair possibly growing around the sides of their heads when they reach an advanced age. For this reason, the male Smurfs wear hats on their heads and rarely show their bald heads in public.

There are also humans in mainstream Smurfs media that are bald or balding. Gargamel, the Smurfs' main nemesis, is bald mostly on the top of his head. Hogatha the witch is completely bald and thus wears an orange wig on her head. Lord Balthazar is presumably head and thus wears a gold helmet on his head.