Stuttering, also known as stammering, is a speech disorder characterized externally by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses called blocks in which the person who stutters is unable to produce sounds. Almost 80 million people worldwide stutter, about 1% of the world's population, with a prevalence among males at least twice that of females. Persistent stuttering into adulthood often leads to outcomes detrimental to overall mental health, such as social isolation and suicidal thoughts.