Why are my mouth corners turning down when I smile? (Photos)

Facial aesthetics especially on young people is primarily based on facial skeletal structure.
Soft tissues tend to be fairly consistent from person to person.
I don’t see the corners of your mouth turning down but see premature development of a marionette lines.
Marionette lines are complex and difficult to treat.
The most common treatment is to use fillers but the problem is not based on a loss of volume so adding fillers often doesn’t give much improvement.
The corners of the mouth are highly complex anatomic areas that are influenced by many different muscles a facial expression which in the end have their origin at different points on the facial skeleton.
Manipulation on this part of the face is very difficult to do.
Some providers try to correct some of these issues by weakening the depressor anguli oris muscle using Botox.
My experience doing this treatment is the smile becomes wider but it does not turn up the corners of the mouth the way some other providers claim.
Best,
Mats Hagstrom MD

Your smile looks great, You can try Botox to help a little and the good news is if you don't like it it will go away! See an expert injector. Best of luck!