Some types of stress increase stuttering. Some types of stress decrease stuttering. Other types of stress have no effect on stuttering.

Physiological stress, such as elevated heart rate, has no effect on stuttering. No study has found that sleep deprivation, the flu, etc., increases stuttering.

Emotional stress often reduces stuttering. Many stutterers report being "so scared" that they "couldn't stutter." There is a neurochemical explanation, based on the interaction of adrenaline and dopamine.

Time pressure, cognitive stress (e.g., trying to talk to someone who is watching television), and speech-related fear and anxiety (such as fear of public speaking) increase stuttering.

Several studies have found that distractions do not reduce stuttering.