Is stuttering fully neurological?

Is stuttering fully neurological? Been confusing me for a while if my stutter is neurological or psychological. I've been stuttering since 5 and still do but since I've finished my school and responsibilities started to kick in I've been more concerned about it. I usually don't stutter with my friends and I'm 90%fluent but that 10% scares the shit out of me and it's very random. So i was wondering can stuttering be jus caused due to psychological factors or its completely related on how your brain functions. Also I noticed i stutter more around certain people and stutter the words which I feel I can't the most.