What is the ruling on a beard that only grows on the sides and resembles the hairstyles of non-Muslims – should it be shaved to differ from them, or left? And what is the ruling on treating it, which necessitates shaving it, and is it permissible to stop the treatment in the future if it leads to its shedding?

The presence of a gap in the beard (especially at the age of 18, when it is gradually growing) does not justify shaving it. Rather, it must be let grow and honored, because it is a religious requirement, even if it is sparse, or others have adopted it, or it resembles a certain style. If the situation persists and is bothersome, stimulating hair growth medications can be used.