Stuttering is a speech disorder that affects the rhythm and flow of speech, characterized by repetition of sounds, syllables, or words, prolongation of sounds, and interruptions in speech known as blocks. The exact cause of stuttering is not fully understood, but researchers believe that it is caused by a combination of factors, including genetics, language development, environment, and brain function.

Developmental stuttering is more common in some families, and it may be passed down from parents to children. Stuttering usually begins in early childhood when speech and language skills are expanding and other developmental learning is taking place, typically between the ages of 2 and 5. As children produce longer and more complex sentences, their brain experiences higher demand, which can affect the motor control necessary to produce speech. When motor pathways can’t keep up with language signals, stuttering can occur.

Stress, anxiety, and negative emotions related to speaking may increase tension and further affect a childs ability to communicate. Stuttering may be worse when the person is excited, tired, or under stress, or when feeling self-conscious, hurried, or pressured. Situations such as speaking in front of a group or talking on the phone can be particularly difficult for people who stutter.

In rare cases, stuttering is the result of brain injury or severe psychological trauma, known as "acquired" stuttering. However, most people who stutter begin stuttering in childhood during the developmental period in which they are learning to communicate.

There is no cure for stuttering, but early treatment can prevent stuttering from continuing into adulthood. Different techniques are used to teach children skills that can help them speak without stuttering, such as slowing down speech and learning to breathe while speaking. Complications of stuttering may include social anxiety, low self-esteem, and negative impact on job performance and opportunities.