What causes a lisp?!
Question: What causes it?
Answers: What causes it?
So there are lisp lisps, and lateral lisps.
'normal' lisps are when the flow of air for 's', and 'z' to some extent, is not directed between your tongue and alveolar ridge (roof of mouth just behind teeth), but between your tongue and teeth. This can be structurally based or just bad habit.
lateral lisps are when the air is directed via the sides of the mouth, for example along between the cheeks/teeth. These are pretty rare and sound very 'slushy'.
These changes in air flow cause a change in the turbulence of the sound and, unfortunately for people who lisp, people notice the change.
Missing or misaligned front teeth
also something with muscles in the tongue I think
I have a lisp, and for me, it is not putting my tounge up behind my top teeth when i say S's