What Is a Lisp? Types, Causes, Treatment & Assessment

A lisp is a common speech sound disorder that affects the way certain speech sounds are produced. People with a lisp often have difficulty pronouncing sounds such as /s/ and /z/ clearly, causing speech to sound distorted or less intelligible.

While some forms of lisping are a typical part of speech development in young children, persistent lisping may require assessment and treatment from a speech pathologist.

What is a Lisp?

A lisp occurs when the tongue is positioned incorrectly during speech, affecting airflow and the production of certain sounds. The speech sounds most commonly affected are known as sibilants, which include:

• /s/
• /z/
• /sh/
• /zh/
• /ch/
• /j/

A lisp is one type of speech sound disorder, sometimes referred to as a speech disorder lisp, because it specifically affects articulation rather than language development. A person with a lisp generally knows what they want to say but has difficulty producing certain speech sounds accurately.

Many children temporarily lisp while learning to coordinate the complex movements of the tongue, lips, jaw, and breath required for clear speech. However, when lisping continues beyond the expected age of speech development, intervention may be beneficial.

Types of Lisps

There are several types of lisps, each characterised by different tongue positions and airflow patterns.

Interdental lisp

With an interdental lisp, the tip of the tongue protrudes between the front teeth when producing sounds such as /s/ and /z/. This results in sounds that resemble the “th” sound.

Examples include:

• Sun → Thun
• Soup → Thoop
• Sister → Thister

Interdental lisps are frequently seen in young children and may resolve naturally as speech develops. However, if the pattern continues into later childhood, speech therapy may be recommended.

Lateral lisp

A lateral lisp occurs when air escapes over the sides of the tongue instead of flowing through the centre of the mouth. Unlike interdental lisps, lateral lisps are not generally considered a typical developmental stage and often needs speech therapy to correct the underlying airflow and tongue placement pattern.

A lateral lisp may affect /s/, /z/, /sh/, /ch/, and /j/ sounds

For example, /s/ sounds become /sl/ sounds. ‘Sun’ becomes ‘slun’.

Speech therapy for a lateral lisp focuses on retraining the tongue and airflow, teaching the child to direct air through the centre of the mouth and guiding the tongue into the correct position for each affected sound. With consistent practice, most children go on to produce these sounds clearly.

Dentalised Lisp

A dentalised lisp is similar to an interdental lisp, but the tongue presses against the back of the front teeth rather than protruding between them.

The distortion is often more subtle, but speech may still sound unclear or imprecise.

Palatal Lisp

A palatal lisp occurs when the middle of the tongue touches the roof of the mouth during speech.

This type of lisp is less common and can significantly affect speech clarity. Assessment by a speech pathologist is often recommended when a palatal lisp is suspected.

What is the Cause of a Lisp?

There are several possible causes of a lisp:

• Normal speech development
  Many toddlers will naturally go through a stage of lisping as they learn to coordinate the complex mouth movements required for speech. This usually resolves on its own by age 3-4.
  Because complex speech sounds such as /s/, /z/, and /sh/ require precise tongue control, some children temporarily lisp as they learn these skills. In many cases, speech naturally becomes clearer with age and practice.

• Dental issues
  Gaps between teeth, missing teeth, or misaligned teeth can cause a lisp. Braces may temporarily cause lisping too. Speech sometimes improves once dental issues are addressed.

• Oral structure
  Some children have structural differences that make correct tongue placement more difficult.

These may include:

• • Tongue-tie (ankyloglossia)
  • A high or narrow palate
  • Jaw structure differences
  • Oral muscle weakness

These factors can contribute to persistent articulation difficulties

• Neurological issues
  Conditions like cerebral palsy, hearing impairment, or cleft palate can contribute to speech difficulties.

• Behavioural habits
  Thumb sucking or tongue thrusting can encourage fronted tongue placement.

If the lisp persists past age 3-4 with no dental or structural cause, it is likely a speech sound disorder that requires speech therapy.

Effects of an Untreated Lisp

A persistent lisp can lead to:

• Difficulty communicating clearly
• Frustration, shyness, or embarrassment
• Teasing from peers
• Lower self-esteem

This may cause some children to avoid speaking. Early treatment is recommended to prevent any negative social or emotional consequences.

How is a Lisp Treated?

Speech therapy is the main treatment for lisping. A speech-language pathologist will work with the child on:

• Tongue, lip, and jaw exercises to improve coordination
• Correct tongue placement for sibilants
• Practice words, phrases, sentences with target sounds
• Building confidence using new speech patterns in everyday conversations

For children, parents and caregivers often play an important role by encouraging practice at home and reinforcing speech goals.

With consistent speech therapy, most children can achieve clearer speech and improved communication confidence.

How does Speech Pathologists assess lisp?

A speech pathology assessment helps determine whether a lisp is present, identify the type of lisp, and develop an appropriate treatment plan.

The assessment may include:

Case History

The speech pathologist will discuss developmental, medical, hearing, and educational history, as well as any communication concerns.

Speech Assessment

Speech sounds are evaluated during activities such as conversation, picture naming, reading, and word repetition. This helps identify which sounds are affected and how they impact overall speech clarity.

To evaluate speech sound production, a speech pathologist may use word lists or sentences containing multiple s, z, sh, and ch sounds. These phrases can help identify characteristics of an interdental lisp or lateral lisp and provide a baseline for measuring progress during therapy.

Oral Mechanism Examination

An oral examination may assess tongue movement, lip function, jaw coordination, palate structure, and dental alignment to identify any physical factors contributing to speech difficulties.

Recommendations

Following the assessment, the speech pathologist will explain the findings and recommend whether monitoring, speech therapy, home practice, or further referrals are required.

How Can Allied Kids Therapy Help?

Our team of experienced speech pathologists specialises in assessing and treating lisps and other speech sound difficulties in children of all ages. We understand that every child develops speech differently, so each assessment and treatment plan is tailored to your child’s individual needs.

When you come to us with concerns about a lisp, our process typically looks like this:

• Initial assessment: we take a full case history and evaluate your child’s speech sounds through play-based and structured activities to identify the type of lisp and its likely cause
• Personalised treatment planning: we explain our findings clearly and develop a therapy plan built around your child’s specific sound errors and goals
• Ongoing therapy sessions: our speech pathologists use engaging, evidence-based exercises to build correct tongue placement and airflow, tracking progress along the way
• Family involvement: we work closely with parents and caregivers, offering practical strategies to reinforce speech goals at home

If you’re concerned about a lisp or other speech sound difficulties, our speech pathology team can help. Learn more about our speech pathology services.

Make a referral or contact our team to discuss how we can support you and your child.