Stuttering is due to an imbalance of signalling molecules in your brain called neurotransmitters. The main neurotransmitter effected is dopamine. Dopamine is responsible for initiating and maintaining movement within the body, and when effected, there can be issues with coordinated movement. There has been some genetic causes to stuttering, but definitely anything that effects dopamine levels in the brain such as stress (public speaking, large crowds), smoking, poor mental health can all exacerbate a stutter. That’s why it’s very important to maintain a good healthy sleep schedule, work out, exercise, and do mental exercises like meditating, which can bring a calm relaxed mind and balance out those dopamine levels, ultimately aiding speech fluency! Hope that helps :)