My Kid Can’t Say his S and Z sounds!: What is a Lisp?

Part 1 of 3-Part Series on Lisps and Tongue Thrusts


One of the biggest questions I get as a speech therapist is in regards to what we call a ‘lisp’.  I hear things like, ‘Should I worry if my child says ‘thick’ for ‘sick?’ or ‘When should I worry about it?’  Unfortunately, there is no simple answer to that question and many variables come into play as far as when we would intervene as speech pathologists.  I did, however, want to shed some light on the subject and hopefully provide some insights to parents and caregivers in this area so that you do know when to ‘make the call’ to your speech pathologist and how to best support good oral development at home. This is Part 1 of a 3- Part series that will dive into this topic!

What is a lisp?

A ‘lisp’ is a term that most often refers to a difficulty pronouncing the ‘s’ and ‘z’ sounds but is essentially referring to a specific type of functional speech disorder (affecting a very specific ‘family’ of sounds).  The most familiar explanation is when a person produces a ‘th’ sound in place of an ‘s’ or ‘z’ sound (‘thoup’ instead of ‘soup)’. What many people don’t know is that there are 4 different types of lisps with a range of severities and differences in how they impact speech.

Types of Lisps

  1. Interdental Lisp (or frontal lisp):  With an interdental lisp, the tongue protrudes forward between the front teeth when producing ‘s,z’ sounds, frequently making them sound like a ‘th’ sound.  There are differing opinions/data out there about whether this is a ‘normal’ or ‘typical’ part of child speech development (not all children go through this!) but one of the more commonly held beliefs in the field is that this may be developmental in nature and children should outgrow this by age 4 ½. There are differing schools of thought on this, which I will discuss in a later blog!

  2. Dentalized Lisp:  This one isn’t considered an official diagnostic term but it essentially refers to a distortion of the ‘s,z’ sounds because the tongue is pushing forward into the back of the front teeth.  This forward tongue position, contacting the teeth, will understandably disrupt airflow for these sounds and result in a distorted or muffled sound. Similar to the interdental lisp, this is often thought to be ‘developmental’ in nature and that children will hopefully ‘outgrow’ it (by 4 ½).

  3. Lateral Lisp:  With this lisp pattern, a child’s tongue tip is (often) lifted and anchored behind the teeth (think tongue position of ‘L’) with an ‘s,z’ production and the airflow is directed over the sides of the tongue instead of down the middle.  This often results in ‘slushy’ or ‘wet’ sounding speech. Unlike the interdental lisp, this is NOT a part of typical speech development and, therefore, should be addressed with intervention as soon as possible, even in those early preschool years.

  4. Palatal Lisp:  This is the least common lisp pattern, characterized by the mid-section of the tongue coming in contact with the hard or soft palate (the upper roof of the mouth) with an ‘s,z’ production.  Similar to the lateral lisp, this is NOT a typical pattern in speech development and should be addressed as soon as possible.

When to Intervene

So as a starting point, we first need to identify what type of lisp we’re seeing, AND the severity.  Is it one that may be more ‘developmental’ in nature like an interdental or dentalized production, in which case we may wait until 4 or later to intervene (dependent on child’s readiness)?  Or is it an ‘atypical’ (i.e. NOT developmental) lisp that requires more immediate intervention like a palatal or lateral lisp? Understanding exactly what type of lisp is occurring, the level of impact on speech intelligibility and the age and readiness of the child are all big determiners on ‘when to treat’.  For example, if the child is very difficult to understand due to this speech error, particularly by age 4, that would indicate treatment is necessary sooner rather than later. This is especially true if the child is open and ready for the therapy process. However, if you have a younger child who simply can’t yet attend to or imitate the models and instructions you give them, that may be reason to wait a bit. So for younger/preschool aged children in particular, it’s important to determine when to intervene based on the individual child and their readiness. In my professional opinion, jumping on treatment sooner rather than later is always better. The longer a child continues with an incorrect speech pattern, the stronger that habituated pattern will be and the more difficult it becomes to change. I have also found that while some literature in my field believe the interdental or dentalized lisp is ‘developmental’ in nature (i.e. they may grow out of it with age/maturation) and prefer to wait on treatment, I have seen many lisps continue way beyond the age of 4 and find that many children need intervention to correct this pattern. Lastly, you want to think about the presence (or absence) of the child’s 2 top front teeth. Beginning speech therapy for a lisp should be dependent on the child HAVING those 2 front teeth (either baby teeth or adult teeth). If the baby teeth have fallen out and there is a space while adult teeth are waiting to come down, this is not helpful (and can be a hindrance) to speech therapy so you’re best to address this either before those teeth fall out or after they have grown at least half way in. Here is a helpful article from the resource section of my website about Lisps and When to Treat (scroll to the bottom of the page).

There is another big consideration that should be explored when clients come to us with an obvious s/z error production, which is identifying the existence (or not) of a tongue thrust. Stay tuned for part 2 of this blog series (Tongue Thrust: What is it and why should I care?) for more information on signs and causes of tongue thrust and its impact on our kids’ speech and oral development.