Stuttering affects nearly 3 million children and adults of all ages in the United States. As children grow up and develop their language skills, up to 10% will experience a stutter for some period of their life.

The majority of children, approximately 75%, will outgrow their stutter eventually over several months or years. For the remaining children, stuttering can persist into adulthood if left untreated, potentially turning into a lifelong communication disorder.

But what exactly are the causes of stuttering? In this post we will review the basics of stuttering and why it occurs.

What Is Stuttering?

We misspeak from time to time or have natural sound repetitions. Occasional stutters (also called disfluencies) are not considered clinical stuttering. Clinical stuttering is when a person consistently produces disfluencies and has trouble fluently producing sounds and words.

Let’s review a little about the different types of stuttering.

  • Repetitions: Repetitions are a type of dysfluency where a word, syllable, or sound is repeated more than three times. Example: “I w-w-w-w-w-w-want to go to the store.”
  • Prolongations: Prolongations are a type of dysfluency where a sound is prolonged or held for an abnormally long period of time. Example: “I fffffffffffffffffound a penny.”
  • Blocks: The last kind of dysfluency or stutter is called a block. When a block occurs, no sound is made in the mouth or throat. The parts of the mouth are stuck in one position and unable to continue to move for a period of time. Example: “I w------------------ant to go to the park.”

Now that we have covered the basic types of dysfluencies, let’s discuss some of the most common causes of stuttering.

What Causes a Stutter?

Genetics and Family History

Research has shown that there is likely some kind of genetic relation to stuttering. Case histories have shown that many people who stutter also have family members who stutter. However, the National Stuttering Association has also stated that there does not seem to be a link between the severity of stuttering in family members.

In other words, a person may be more likely to stutter if they have family members stutter, yet each family member may experience different levels of severity.

Motor Planning and Brain Function

There is reason to believe that those who stutter likely have differences in speech-motor control, such as coordination and timing. Abnormalities in these areas can result in stuttering.

According to the National Stuttering Association, brain imaging studies have also shown that those who stutter have more right brain activity than left brain activity. Language is processed and planned in the left hemisphere. Less activity in the left brain may negatively impact a person’s speech fluency.

Language Processing

There has been research to suggest there could be a connection between language processing/word retrieval and stuttering. People who do not stutter have shown more proficient abilities in receptive language as well as word retrieval. Those who stutter have shown more problems tied to word finding. An increase in response times can increase chances of stuttering due to stalling of speech, and possibly even perceived pressure to speak faster.

Communication Environment/Emotion

It is not uncommon for those who stutter to have more difficulty speaking in a communication environment that is more tense or emotional. Likewise, some people may find that they stutter more frequently around people of certain personalities.

Due to heightened emotion or anxiety, breathing can sometimes become more shallow or inconsistent. The vocal tract and articulators may also exhibit more tension because of this. We will review more about breathing in the next section.

What Physically Happens During Stuttering?

Now that we have covered some of the root causes of stuttering, let’s talk a little about what physically happens in a stuttering event, and how this negatively impacts speech fluency.

Speech first begins with breath. We inhale and we exhale. As we breath out, our vocal folds come together and vibrate when we initiate our voice. The air we breathe out and the vocal folds work together to produce adequate sound. That sound is then shaped in the oral cavity to produce different types of sounds. For example, when we pronounce the /d/ sound, the tongue comes up and taps behind the teeth to create this particular sound. When pronouncing /r/, the tongue tenses and moves backwards in the mouth to produce this sound.

If there is any tension in any area of the mouth or throat, this can cause stuttering. If a person is stuttering on the /d/ sound, and repeating it over and over, then there is likely tension in the tongue muscles.

If a person is trying to say the /f/ sound and it is coming out as a prolongation (example: “ffffffff”) then there could be some tension in the lips or jaw contributing to the stutter.

It is important to note that there could also be a lack of breath support contributing to all of this. If we do not have enough air (breath) to speak on, then it can feel like we are trying to squeeze out every sound. This can result in the tension.

Appropriate breathing for speech is called diaphragmatic breathing. This can also be referred to as belly breathing. This is because when we take diaphragmatic breaths, the diaphragm moves downwards. This allows our lungs to expand as we breathe in, then moves back in place as we breathe out.

You can try this yourself. Before you take your first breath, place your hand on your belly. You should be able to feel your belly move out then back in. If your hand moves in this pattern, you will know that you are breathing correctly!

When using this type of breathing during speech, make sure to control your breath. This means that you should be able to speak during one exhalation without feeling like you are running out of air. This takes practice for those who struggle in this area. However, once it is learned it will very much help speech fluency!

How to Manage a Stutter and Speak More Smoothly

There are many helpful resources available to find additional education about stuttering, along with techniques you can practice at home or with a speech therapist to improve fluency. To start, we've compiled an in-depth resource guide that answers some of the most foundational questions about stuttering.

Expressable Online Speech Therapy | Stuttering and Fluency

We've also written a number of blogs that explore different aspects of stuttering. These include: