Why Do People Have Lisps and How Do They Affect Speech
Why do people have lisps? A lisp happens when the tongue does not move into the precise position needed for clear s and z sounds. In many cases, a lisp develops from a combination of learned speech patterns, differences in oral structure, tongue thrust, hearing factors, or other speech-motor challenges.
Lisps are among the most common speech sound errors seen by speech-language pathologists. According to the American Speech-Language-Hearing Association's 2022 Schools Survey, speech sound disorders account for about 23 percent of school-based speech-language pathologists' caseloads. That prevalence makes lisp speech therapy one of the most common services speech-language pathologists provide.
The guide below explains the common causes of a lisp, the four main types of lisps, how lisps can affect everyday communication, and the treatment options available for children and adults. A lisp reflects a difference in speech sound production, not intelligence.
Key Takeaways
A lisp is a speech sound disorder that affects the production of s and z sounds. A lisp occurs when the tongue and airflow do not work together in the way needed for clear speech, causing s and z sounds to come out distorted.
There is no single cause of a lisp. Differences in tongue movement patterns are common, but tongue thrust, oral structure differences, hearing loss, and neurological factors can also contribute. In some families, speech sound difficulties may occur across generations.
There are four main types of lisps: frontal, dental, lateral, and palatal. Frontal and dental lisps can be part of typical speech development in young children. Lateral and palatal lisps are less common and generally warrant evaluation by a speech-language pathologist.
Speech therapy can help correct a lisp at any age. A speech-language pathologist identifies contributing factors, teaches correct tongue placement and airflow patterns, and helps clients carry those skills into everyday conversation.
What Causes a Lisp? The Common Reasons
When Is a Lisp Normal? Development and When to Seek Help
How Speech Therapy Helps Correct a Lisp
What Is a Lisp?
A lisp is a speech condition that changes how a person produces the s and z sounds. Speech-language pathologists classify it as a type of articulation disorder because it affects how a sound is produced rather than language or thinking skills. A lisp develops when airflow escapes incorrectly during speech, creating a distortion that listeners can often recognize.
To produce a clear s sound, the tongue tip rests just behind the front teeth, the sides of the tongue contact the back teeth, and air flows in a narrow stream down the center. When that tongue position changes, the sound can become distorted. A lisp is often called a speech impediment. Speech-language pathologists usually use more specific terms, such as speech sound disorder or articulation disorder, to describe the underlying speech difference.
A lisp is one specific pattern within the wider world of articulation and speech sound development. Naming it accurately matters because both what causes a lisp and the right plan depend on which sounds are affected and why.
How Lisps Affect Speech and Communication
A lisp affects the clarity of s and z sounds, which occur frequently in everyday speech. Because those sounds appear in so many words, a noticeable lisp can make some speech harder to understand, especially in fast conversations or noisy environments. For most people, the main impact is on speech clarity rather than the message itself.
A lisp can also affect confidence in certain situations. Some people rarely think about it, while others become more aware of it during presentations, introductions, job interviews, or important conversations. The experience varies from person to person.
What Causes a Lisp? The Common Reasons
So why do people develop lisps? In most cases, a lisp results from a combination of physical, developmental, or learned factors rather than a single clear trigger. Speech pathologists sort what causes a lisp into the groups below, and a misplaced tongue sits at the top of the list.
Tongue Placement and Learned Habits
Incorrect tongue placement is the most common reason a lisp occurs, and it is what most often causes a lisp in the first place. Many people learn to make the s and z sounds with improper tongue placement, and the habit sticks due to muscle memory.
A habit of pushing the tongue forward can also lead to a lisp. When the tongue pushes forward during speech, as it does with tongue thrust, an orofacial disorder, the tongue pushes the s out of place and drives a frontal lisp. Prolonged thumb sucking and prolonged pacifier use can also lead to learned lisping behaviors, because these habits can alter the natural shape of the palate and jaw.
Structural and Anatomical Differences
A lisp can also develop from anatomical or dental issues, and these anatomical factors are common in older children and adults. A tongue-tie, a short band of tissue under the tongue, can limit tongue movement and lead to incorrect production of the s sound. Narrow dental arches, a misaligned jaw, missing baby teeth, or unusual tongue size can all leave room for the tongue to slip out of position.
Jaw misalignment can contribute to the development of a lisp. These structural differences in the oral cavity change the space the tongue muscles have to work in, so the s and z sounds drift off target. Weak tongue muscles can play a part, too, since muscle weakness makes the precise movement required for a clear s sound harder.
Neurological and Developmental Factors
Some lisps trace back to neurological factors. Conditions like cerebral palsy can affect the muscle control involved in speech production, so a person cannot correctly produce certain sounds. In these cases, a lisp is one part of a broader motor picture that a speech therapist assesses carefully.
A lisp can also appear alongside speech delays or other differences in a child's speech development. Those developmental differences are why two children with the same lisp often need different plans.
Hearing, Genetics, and Family History
Hearing differences can contribute to a lisp in some cases. Children learn speech sounds by hearing them and comparing what they hear with what they produce. When hearing loss reduces access to high-frequency sounds, including s and z, accurate development of speech sounds may become more challenging.
Family history may play a role in some cases. Children with close relatives who have speech sound disorders can be more likely to experience similar speech difficulties. Researchers are still working to understand how genetic factors, speech development, and environmental influences interact, and no single inherited cause of lisps has been identified.
Acquired and Adult Lisps
Most lisps begin in childhood, but a lisp can also appear later in life. An adult-onset pattern like this is called an acquired lisp, and it develops when something changes the space or the muscle control inside the mouth. People search for why they suddenly have a lisp more often than expected.
Dental work, new dentures, or an orthodontic device like Invisalign can shift the space the tongue works in and nudge the s and z sounds off target. Neurological conditions can also result in acquired lisps later in life, when a health event affects the muscles or nerves involved in speech. Many adults also carry a lisp from childhood, and it can persist into adulthood if left uncorrected.
Understanding What Causes a Lisp in Adults: Strategies for Improvement
Find out what causes a lisp in adults in this blog.
The Four Main Types of Lisps
There are four main types of lisps, and naming the type is the first step toward correcting it. Each one comes from a specific tongue position and changes the s and z sounds in its own way. You can go deeper in our guide to the types of lisps.
Frontal (Interdental) Lisp
A frontal lisp, also called an interdental lisp, is the most common type. An interdental lisp occurs when the tongue protrudes between the teeth, so the s turns into a “th” sound and sun comes out as thun. It shows up in many young children and often fades as the adult teeth come in.
Dental Lisp
A dental lisp is closely related to the interdental lisp, but the tongue touches the back of the front teeth instead of poking through them. A dentalized lisp occurs when the tongue touches that spot, giving a muffled s rather than a clear th. Together, these are the two most common kinds seen in early childhood.
Lateral Lisp
A lateral lisp causes air to escape over the sides of the tongue. That gives the s and z sounds a wet, slushy quality. It is not part of typical development, so it is worth having a speech therapist take a look.
Palatal Lisp
A palatal lisp is the least common type. It involves the tongue pushing against the soft palate, the soft tissue toward the back of the roof of the mouth, which makes the s sound more like sh. Palatal lisps occur far less often, and like the lateral kind, they rarely clear up on their own.
When Is a Lisp Normal? Development and When to Seek Help
Some lisping can be a normal part of speech development. Frontal and dental lisps are often seen in young children, especially during the preschool years, while speech sound skills and oral motor coordination are still developing. Many children outgrow these patterns over time, although some continue to need speech therapy.
Typical speech development provides a rough timeline to watch for. Correct production of the s and z sounds is usually acquired by age 4 years, 11 months, and some childhood lisps resolve by age six without any help. Most children outgrow a frontal lisp as their adult front teeth, jaw, and coordination mature, often within a few months.
Two patterns are not part of typical development. A lateral or palatal lisp is not a normal developmental variation, so it deserves an evaluation at any age. A child's lisp that persists past a certain age, frustrates the child, or shows up as a lateral or palatal type is a clear reason to reach out to a speech therapist about early speech development.
It also helps to know that children often do not outgrow a lisp without help once it lingers. When a child has a persistent lisp, a brief evaluation helps determine whether to continue monitoring or begin support, and early intervention often leads to faster results. A developmental lisp caught early usually clears with simple treatment methods, so the sooner a child has a lisp addressed, the less practice it takes to say the sound correctly.
How Speech Therapy Helps Correct a Lisp
Speech therapy is often the most effective way to correct a lisp, and it works for children and adults alike. A speech therapist starts with an evaluation to identify which sounds are affected and what is driving the speech error. Speech therapists rely on proven treatment methods and create personalized plans, since the right starting point depends on the cause and the person's goals.
From there, speech therapy builds the sound step by step. It begins with practicing the s sound in isolation, then moves into words, sentences, and finally conversation, so a new s becomes a natural habit. Sessions use cues a person can see and feel, like a mirror for proper tongue placement or a straw to guide the airflow down the center.
How long it takes varies from person to person. Many lisps improve with about three to six months of speech therapy sessions, though an older child or adult who has had a lisp for years often needs longer. Some causes call for a wider team, such as an ENT or dentist for a tongue-tie, or an orthodontist for a bite problem, working alongside the speech therapist.
Practice between sessions speeds progress. Short, frequent reps at home, including the specific exercises a speech therapist assigns, help a child or adult improve pronunciation faster than long, tiring sessions. Our step-by-step video walks families through three at-home exercises, and our full guide explains how to correct a lisp at any age.
Online sessions work especially well for a lisp. Screen-sharing, a mirror, and recorded examples make proper tongue placement easy to model and review from home, and many parents choose articulation therapy for children through our online speech therapy services.
What We See Working With Clients
Speech pathologists rarely hear families ask about a frontal or lateral lisp by name. They come because a first-grader is teased for saying "thun" instead of "sun," or because an adult dreads saying their own name on a work call.
One young client pushed the tongue forward on almost every s sound and had a mild tongue thrust as well. We worked on the resting tongue position and s placement together, and within a couple of months, the child's speech sounded clearer to family and teachers.
An adult client developed a lateral lisp that grew more noticeable after orthodontic work. Using screen-sharing to model where the tongue sits, we redirected the airflow down the center, and within months, they went from avoiding words to speaking freely on calls.
Frequently Asked Questions About Lisps
1. What causes a person to lisp?
A lisp usually comes from incorrect tongue placement during the s and z sounds. There is no single cause, as tongue thrust, tongue-tie, jaw misalignment, hearing loss, and neurological conditions can all contribute. A speech and language pathologist can pinpoint why a particular lisp occurs.
2. Are lisps genetic?
Not directly, but lisps can run in families. Genes help shape the mouth, teeth, and jaw, so a child whose close relatives have speech sound differences is somewhat more likely to develop a lisp. That pattern shows up across some other families too, even though no single inherited cause has been found.
3. Can you suddenly develop a lisp as an adult?
Yes, an acquired lisp can appear in adulthood. Dental work, new dentures, an orthodontic device, or neurological conditions can change the mouth or the muscle control behind speech. If the lisp persists, a speech therapist can help retrain the clear production of s and z.
4. Is a lisp permanent?
No, a lisp is not usually permanent. Some childhood lisps resolve as speech skills develop, while others persist without treatment. Speech therapy can help children and adults improve speech clarity at any age.
5. Can you fix a lisp at home?
Home practice can help, but it is often most effective when guided by a speech-language pathologist. Practicing an incorrect movement pattern may reinforce the distortion rather than correct it. An evaluation can determine whether home practice is likely to be enough or whether speech therapy would be beneficial.
How Connected Speech Pathology Can Help
At Connected Speech Pathology, our speech-language pathologists help children, teenagers, and adults understand and correct a lisp through online speech therapy. A speech-language pathologist begins with a careful evaluation, identifies the type of lisp and its cause, and builds a plan around the sounds and routines that fit each person.
Our online speech therapy services bring focused articulation therapy for adults and children to wherever you are, with sessions shaped around real goals at work, at school, and in daily conversation. Whether a lisp is new or lifelong, we help each client carry clearer s and z sounds into the moments that matter.
Summary
So why do people have lisps? In short, a lisp usually comes from incorrect tongue placement during the s and z sounds, shaped by a mix of structure, learned habits, and sometimes hearing or neurological causes, with no single cause for everyone. The four main types of lisps, frontal, dental, lateral, and palatal, each come from a different tongue position, and a speech therapist can tell the type a child or adult has.
A lisp can affect speech clarity. When a lisp persists or presents as a lateral or palatal lisp, speech therapy can help improve speech production at almost any age. With accurate feedback, targeted practice, and consistent repetition, a distorted s sound can become clearer and more natural in everyday conversation.
About the Author
Allison Geller, M.A., CCC-SLP, is a communication coach, speech-language pathologist, and founder of Connected Speech Pathology, an international online practice providing professional communication coaching and speech therapy for children, teens, and adults. With more than two decades of experience, she has worked in medical and educational settings and published research on aphasia. Today, she leads a team of specialists who help clients improve their skills in public speaking, vocal presence, accent clarity, articulation, language, fluency, and interpersonal communication.
