Botox for the chin is used to treat rhytids, which are wrinkles.
Dynamic rhytids are the creases that appear on your chin. That implies the wrinkles change form depending on the movement of the muscles beneath your skin. The repetition of the identical motions in your muscles causes these forms of rhytids.
When and how your face should move is communicated by your brain and muscles. Acetylcholine is a chemical that allows this communication mechanism to function. Chin Botox works by temporarily blocking the release of acetylcholine.
When Botox is injected into the muscular tissue, the toxin causes the muscles to become immobile. The effect is very momentary, and it does not harm your muscles in any way.