There are many theories and popular beliefs about what causes stuttering. However, despite considerable scientific research from the second half of the 20th century onwards, the cause of the disorder remains a mystery. All we can say at present is that stuttering is most likely due to some problem with the neural processing of the brain areas that support speech production. In other words, individuals inherit a problem where speech muscles won’t do what they should do, when they are needed to do it. However, at present it is not known for certain how that genetic susceptibility works, and the precise nature of the trouble with neural speech processing is not known. The problem begins to appear as young children develop their language skills.
In short, stuttering is thought to be a physical disorder and is not caused by psychological factors such as nervousness or stress, or parenting practices or the way parents communicate with their children when they are young. Nothing about parenting style or the family environment is known to cause stuttering. Stuttering tends to run in families, and it is generally accepted that this is because genetics is involved in the cause. However, the precise nature of the inheritance is unknown at present. Psychological factors such as anxiety or stress can complicate the problem if it persists into late childhood and adolescence.