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

01Definition

What a lisp is

Speech sounds are produced by shaping the airflow with the lips, tongue, teeth and palate. For «s» and «z», the tongue tip rises behind the top front teeth, the sides of the tongue seal against the upper back teeth and a narrow stream of air is directed over the tongue tip onto the teeth. These are called sibilant sounds. A lisp happens when the tongue position or the direction of the airflow is different, changing the quality of these sounds.

Clinicians include lisps among speech sound disorders, specifically articulation errors. A lisp does not affect intelligence or language ability, but it can affect how clearly a person is understood and, for some, their confidence.

02Types

The four types of lisp

• Frontal or interdental lisp: the tongue tip sticks out between the front teeth, so «s» and «z» sound like «th». This is the classic childhood lisp.
• Dentalised lisp: the tongue tip pushes against the back of the front teeth, making the sound muffled or dull.
• Lateral lisp: the airflow escapes over one or both sides of the tongue instead of the centre, producing a wet, «slushy» or spitty sound. It often affects «sh», «ch» and «j» as well. A lateral lisp is not a typical developmental pattern.
• Palatal lisp: the middle of the tongue touches the soft palate when trying to make «s», giving an unusual sound. It is less common.

For an overview of the sounds children typically master at each age, see the speech sound development chart and phonological processes.

03Age

Do children grow out of a lisp?

Many young children produce a frontal lisp while their speech is developing, and most correct it by about four and a half to five years of age. Losing front teeth at around six or seven can cause a temporary lisp that settles when the adult teeth come through.

Lateral and palatal lisps are different: they are not part of typical development and rarely correct themselves. An early assessment is recommended for these, as well as for a frontal lisp that continues after about five years, a lisp that affects how well a child is understood, or a child who is upset about their speech.

04Causes

What causes a lisp

• Learned tongue placement: most lisps have no physical cause; the child has simply learned a different way to make the sound.
• Prolonged dummy (pacifier) or thumb sucking and bottle use: can encourage a forward tongue position.
• Tongue thrust and oral habits: a forward resting tongue position and swallowing pattern; see oral motor exercises.
• Dental and bite differences: an open bite, gaps or orthodontic appliances.
• Hearing problems: difficulty hearing high-frequency sounds like «s» can affect how a child learns them.
• Tongue-tie: a short frenulum can occasionally contribute, although it is a less common cause than often believed.
• Blocked nose and mouth breathing: can encourage a low, forward tongue posture; see mouth breathing.

05Therapy

How speech therapy fixes a lisp

A speech and language therapist first listens to the speech, checks the mouth, teeth, tongue movement and breathing, and screens hearing if needed. Therapy then usually follows a sequence:

• Listening: learning to hear the difference between the correct and lisped sound.
• Placement: finding the correct tongue position with mirrors, visual cues and sometimes tools such as straws or tongue depressors.
• Isolation: producing a clear «s» on its own.
• Syllables and words: practising the sound at the beginning, middle and end of words.
• Phrases, sentences and conversation: making the new sound automatic in everyday speech.
• Home practice: short, frequent practice (5 to 10 minutes a day) is key.

Many children correct a frontal lisp within a few months of regular therapy. Lateral lisps and adult lisps often take longer, but they also respond well. More exercises can be found in speech therapy exercises.

06Adults

Fixing a lisp as an adult

It is never too late to correct a lisp. Adults often seek help for work, public speaking or confidence. The steps are the same as in children, but adults usually progress quickly through the early stages because they can understand detailed explanations and practise independently. The most challenging part is carrying the new sound into fast, spontaneous speech, which needs consistent practice over several weeks to months. Orthodontic work can temporarily change sibilant sounds, and therapy can be timed around treatment.

07Parents

Tips for parents

• Do not correct your child constantly or ask them to repeat words; model the correct sound naturally instead.
• Reduce dummy use after the first year and avoid prolonged bottle use.
• Encourage nose breathing and check for a blocked nose or enlarged adenoids if your child snores or breathes through the mouth.
• Read and play sound games together, emphasising «s» words in a fun way.
• Seek a hearing test if you have concerns about hearing.

09Summary

Key points to remember

• A lisp affects s and z sounds and comes in four types: frontal, dentalised, lateral and palatal.
• Frontal lisps are common in young children and often resolve by about age five.
• Lateral lisps do not usually resolve without therapy.
• Speech therapy is effective in children and adults, especially with regular home practice.