What is a lisp?


A Lisp is a term people use when the /s/ and /z/ sounds are said incorrectly. Other related sounds like “ch” & “sh” may also be affected.

​Part of the child speech development process involves children learning where to put their tongues and lips in order to make all the different sounds in a language. A lisp is when children do not quite get the tongue and lips in the correct place while they are learning to say the /s/ and /z/ sounds. Sometimes this incorrect placement becomes a “habit”. This is why some older children and even adults continue to “lisp”.

​Types of Lisps

There are a few different kinds of lisps. Some would be considered part of “typical speech development” in children and some would be considered a speech impediment.

Types of Lisps


Interdental lisps

This is probably the most common type of lisp.In an interdental lisp is sometimes called a fronal lisp. This is because the tongue comes too forward as the child says the sound. The tongue protrudes between the front teeth and the air-flow is directed forwards. The tongue and teeth positions are the same as when we say the “th” sound. So “sock” sounds more like “thock” and “buzz” sounds more like “buth”.

​Children developing speech along typical paths may have interdental lisps until they are about 4½ - after which they disappear without any help or therapy. If they don't 'disappear' an SLP/SLT assessment is indicated.

​Sometimes the tongue does not go between the teeth but pushes against the teeth. This makes the s “muffled” rather than a full “th” sound.

​Possible causes of an Interdental Lisp:

The “cause” of an inter-dental lisp can just be incorrect placement of the tongue due to a maturing speech system.

​Sometimes a lisp occurs because there is an underlying “tongue thrust” swallow.

​This means the forward tongue position is not only happening as the child is saying the /s/ and /z/ sounds it is happening every time they swallow. This can have an impact on the alignment of their teeth. This is why an assessment by a speech pathologist may 2.be required earlier than 4 years.

​Some children produce many sounds interdentally. Tongue protrusion, or very 'forward' tongue placement may be occurring when the child says not only /s/, /z/, 'sh', 'zh', 'ch' and 'j', but also /n/, /l/ , /d, /d/and other sounds. This is not considered typical development and would be suggestive a speech disorder.

​In some children 'everything' seems interdental. This may sometimes be an indication that the nose is constantly obstructed, due for instance, to allergy, infection, large adenoids or craniofacial anomalies, or may be associated with habitual mouth breathing, tongue thrust, or sucking habits.

Lateral lisp

A lateral lisp is where the middle of the tongue hits the palate instead of the tongue tip touching just behind the teeth when the /s/ and /z/ sounds are pronounced. This tongue placement can make the airflow go to the sides of the mouth rather than straight forward. This is not considered part of typical speech development and hence is considered a speech disorder.

Do I need to worry if my child has a lisp?


This completely depends on the age of the child and the type of the lisp.

​Some children seem to be able to say the /s/ sound perfectly well from 2 years of age.It is however a perfectly normal developmental phase for some (not all) children to produce the interdental lisp on a /s/ and a /z/. This means the child places their tongue on the or between the teeth as they say the /s/ and /z/ sounds until they are about 4½ years of age.

​On the other hand, lateral lips are part of the typical child speech developmental. The speech of a child with a lateral lisp should be assessed an experience speech pathologist. A speech pathologist that also has experience with tongue thrust swallows may also be warranted. Even young children that start to say the /s/ sound with a later lisp should seek advice from a speech therapist.

​Does a lisp impact on the clarity of a child’s speech?

A lisp can reduce clarity to a certain extent depending on how prominent the lisp is. If the lateral /s/ strongly produced words like “mouth-mouse” and “think-sink” may be confused.

​A lateral lisp can make a child’s speech seem very unclear and even spit can gather in the corners of the mouth as the lateral airflow pushes saliva to the side. This can not only reduce speech clarity but also may have self-concept issues later on.

​Some children grow up in an environment where their lisp are not noticed or not considered an issue. Sometimes adults reinforce the interdental lisp by considering it is “cute”..

​Unfortunately, though some children are brutally honest and will point out that the child with the lisp “sounds funny”. They may face ridicule or teasing can be likened to the many “comedy characters that are portrayed with a lisp (e.g., daffy duck!).

​Should I get a speech therapy assessment for my child’s lisp or wait?


Waiting well past 4½ is not advised. The longer the child waits to seek tongue position correction, the stronger the old 'habit' will be. Some younger children may not have the ability to attend or make changes to the lisp however this can be determined with a speech therapy assessment. Sometimes high school students become more aware of their lisps as peer interactions increase in importance. If an older child is motivated to correct the lisp – it is quite possible it can be achieved with the right programme.

​If the child is presenting with a tongue thrust swallow or a lateral lisp early intervention is advised.

Contact SpeechNet Speech Pathology if you have any concerns about your child’s speech.

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Sandra McMahon

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