What Causes a Lisp? Anatomy, Genetics, and Other Risk Factors

Lisps can have several causes, from moving the tongue incorrectly during speech to structural differences in the mouth or tongue. They typically begin in childhood, but this speech condition can affect both children and adults.

Key takeaways

• A lisp results from incorrect tongue position and movement. The tongue obstructs the airflow needed to produce the /s/ and /z/ sounds.
• Several factors can contribute to a lisp, including learning an incorrect tongue position, jaw misalignment, a tongue tie, or a tongue thrust.
• Lisps usually develop in childhood and may continue into adulthood without appropriate treatment.
• There are four types of lisps. Identifying the type is important because it helps guide the treatment approach used in speech therapy.
• A speech therapist can help children and adults with a lisp. Speech therapy trains the tongue muscles to move into the positions needed to produce clear /s/ and /z/ sounds.

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What is a lisp?

A lisp occurs when someone has difficulty pronouncing the /s/ and /z/ sounds. Lisps usually develop during childhood and can persist into the teenage years and adulthood without appropriate treatment. If you or your child has a lisp, you are far from alone. Lisps are among the most common speech errors. An estimated 23% of people who receive speech therapy are treated for a lisp.

There are four different types of lisps. Identifying the type matters because it helps guide the treatment approach used in speech therapy. Here is a brief overview of each one:

1. Interdental, or frontal, lisp

An interdental lisp occurs when the tongue pushes forward between the teeth. When the person tries to pronounce /s/ or /z/, the sound comes out more like “th.”

2. Lateral lisp

A lateral lisp occurs when the sides of the tongue are raised, allowing air to escape around them. A lateral lisp is often described as sounding “slushy” or “mushy.”

3. Dentalized lisp

A dentalized lisp is similar to an interdental lisp because the tongue moves forward. The difference is that the tongue presses between the teeth in an interdental lisp, but against the teeth in a dentalized lisp.

4. Palatal lisp

A palatal lisp occurs when the tongue presses up against the soft palate, or roof of the mouth. This type is less common than the others, but it can still make the /s/ and /z/ sounds difficult to produce.

What causes a lisp in children?

A lisp is an incorrect production of the /s/ and /z/ sounds. It results from an incorrect motor pattern involving tongue position and movement. A person with a lisp places the tongue in a way that obstructs the airflow needed to produce /s/ and /z/. This disrupted airflow creates the lisping sound.

The reason for the incorrect tongue position is not always clear. Several factors can contribute to a lisp, including:

• Learning to produce the /s/ and /z/ sounds incorrectly during childhood
• Jaw misalignment, or another problem with the alignment of the jaw
• A tongue tie, in which the tongue is attached to the bottom of the mouth in a way that limits its movement; this may contribute to a lateral lisp
• A tongue thrust, in which the tongue protrudes forward; this can also affect feeding and swallowing

Are lisps genetic?

The primary cause of a lisp is incorrect tongue placement. However, genetics can influence the structure of a person’s jaw, teeth, and tongue in ways that affect speech and make a lisp more likely.

A family history of speech difficulties may also increase the likelihood that a child will have a lisp.

What is the difference between a tongue thrust and a lisp?

Although a lisp can be a result of a tongue thrust, the two are not the same. Because the distinction can be difficult to identify, it should be determined by a speech therapist.

A tongue thrust is an orofacial myofunctional disorder (OMD). It occurs when the tongue moves forward noticeably while a person is speaking or swallowing. The tongue may rest too far forward in the mouth or push between the teeth during speech and swallowing.

Like a lisp, a tongue thrust can cause articulation errors that affect how a person produces sounds.

What causes a lisp in adults?

An adult lisp can result from any of the factors listed above. Many people receive treatment for a lisp during childhood or adolescence. Without speech therapy, however, a lisp may continue into adulthood.

Related guides

A Complete Guide to Lisps: Types, Causes, Diagnosis, and Treatment

What Is a Lisp? Types, Causes, and Speech Therapy

Can You Correct a Lisp? Home Exercises vs. Speech Therapy

Lateral Lisps: What They Sound Like and How to Correct Them

Can you outgrow a lisp?

A lisp may go away on its own. However, if it persists beyond age 5, speech therapy may be needed to correct it.

It is important to recognize that an interdental lisp can be a normal part of development. A 2020 clinical review assessed the ages at which children typically produce each speech sound correctly. The studies included in the review found that children typically acquire correct /s/ and /z/ production by age 4 years, 11 months. Up to that age, an interdental lisp could technically be considered a normal part of development.

It is also important to recognize that not everyone wants to change how they speak. Most adults are aware of the way they communicate, but the effect of a person’s speech on their life and career varies. For some people, lisping is not necessarily a negative.

How is a lisp treated?

A speech-language pathologist can help both children and adults with a lisp. During a detailed speech evaluation, the speech therapist can identify the type of lisp and develop a specific program that targets tongue placement.

Speech therapy for a lisp trains the tongue muscles to move into the positions needed to produce clear /s/ and /z/ sounds. Depending on the person’s needs, treatment may also address other speech sounds, or phonemes.

Speech therapy for a lisp trains the tongue muscles to produce clear /s/ and /z/ sounds.

Weekly speech therapy is usually recommended for people working on /s/ production. The speech therapist will identify the best point at which to begin practicing the /s/ sound. This step matters because progress when learning a new sound depends in large part on starting at the right level.

For example, someone who cannot pronounce /s/ correctly by itself should not begin by practicing the sound in phrases. Speech therapy first focuses on producing /s/ in isolation. Practice then progresses to /s/ in syllables, words, and increasingly complex contexts. The person works through a series of smaller goals on the way to producing /s/ correctly in everyday conversation.

Speech therapy also targets a sound according to where it appears within a word. Here are examples of /s/ in different word positions:

• Initial word position = soup
• Medial word position = messy
• Final word position = class

Moving through these stages takes time, but following a structured plan supports progress over the long term.

If you are concerned about your child’s speech or your own, contact a speech therapist for an evaluation. Early intervention is always recommended, but adults can benefit from speech therapy too. A lisp can be corrected at any age.