What Is a Lisp? A Speech-Language Pathologist Explains
What is a lisp? A lisp is a speech sound disorder that affects how the s and z sounds are produced. A lisp occurs when the tongue is positioned incorrectly during speech, which can make words sound unclear. For example, sun may sound like thun, or zoo may sound like thoo.
Lisps often appear in young children as they learn to speak and may continue into the teen or adult years.
There are four main types of lisps, each linked to a different tongue position. Some resolve naturally as a child develops, while others benefit from support from a speech-language pathologist. The good news is that a lisp can improve at almost any age with targeted practice.
The guide below explains what a lisp is, the different types of lisps, common causes, and how treatment can help both children and adults.
Key Takeaways
A lisp is a speech sound disorder that affects how the /s/ and /z/ sounds are produced. It happens when the tongue is positioned incorrectly during speech, which can make those sounds seem distorted or unclear.
There are four main types of lisps: interdental, dentalized, lateral, and palatal. Each type changes speech in a different way because the tongue moves differently during sound production.
Most lisps relate to tongue placement patterns. Tongue thrusting and differences in dental alignment are common contributing factors. A speech-language pathologist can identify the factors affecting speech and teach more accurate sound production.
Both children and adults can improve a lisp with speech therapy. Some children develop clearer speech within a few months, while older children and adults often benefit from consistent, focused practice.
How Speech Therapy Helps Correct a Lisp
What We See Working With Clients
What Is a Lisp?
A lisp is a speech sound disorder that affects how a person makes the /s/ and /z/ sounds. Some call it a functional speech disorder, because it stems from how the sound is made rather than from an injury. It is one of the most common speech challenges that speech pathologists treat, accounting for about 23% of their caseload.
To produce a clear /s/, the tip of the tongue sits just behind the front teeth at the alveolar ridge, the bumpy spot on the roof of the mouth. Its sides press up toward the back teeth, and air flows in a thin stream down the center. A lisp happens when that placement or airflow goes off track, so the same sound comes out distorted.
People often ask whether a lisp is a speech impediment. Today, speech-language pathologists typically classify a lisp as a speech sound disorder because it affects how certain sounds are produced. It is different from a language delay.
The Four Types of Lisps
In speech-language pathology, there are generally four commonly recognized types of lisps. Each type comes from a specific tongue position, and each one changes the /s/ and /z/ sounds in its own way. You can go deeper in our guide to the types of lisps.
Interdental (Frontal) Lisp
An interdental lisp, also called a frontal lisp, is the most common type of lisp. The tongue moves between the front teeth when producing /s/ and /z/, making those sounds resemble /th/. For example, sun may sound like thun. The pattern shows up in many young children.
Dental Lisp
A dental lisp is closely related to the interdental type, but the tongue presses against the back of the front teeth instead of poking through them. The result is a muffled "s" rather than a clear th. Together, they are the two most common types seen in early childhood.
Lateral Lisp
A lateral lisp happens when air escapes over the sides of the tongue instead of flowing down the center. That gives the s and z a wet, slushy quality, which is why some people call it a slushy lisp. 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. The middle of the tongue lifts and touches the roof of the mouth toward the back, making the s sound more like sh. Like the lateral kind, it rarely clears up on its own.
What Causes a Lisp?
Most lisps are related to tongue placement and movement, though physical differences in the mouth can sometimes contribute. Understanding what causes a lisp can help parents decide whether a child is likely to outgrow it or may benefit from support. Common causes include:
Incorrect tongue placement. Many children simply learn the sound with the tongue in the wrong spot, and the habit sticks without any physical cause.
Tongue thrust. When the tongue pushes forward during speech and swallowing, it can cause an interdental lisp, and tongue thrust often responds well to focused treatment.
Tongue tie. A tight band of tissue under the tongue, known as ankyloglossia, can limit movement and make some sounds harder to produce.
Dental and jaw alignment. An open bite, an overbite, or gaps between the teeth can leave room for it to slip out of place.
Prolonged thumb-sucking or pacifier use. These habits can shift the teeth over time and change how they rest.
Mild hearing loss. A child who does not hear the s and z clearly can have trouble pronouncing them correctly.
Genetics. A child's genes can shape how the mouth and jaw develop, so lisps sometimes run in families.
Lisps in Children and Adults
Lisps affect children and grown-ups alike, though the path looks a little different for each.
Lisps in Children
Many lisps are a normal part of speech development. As children learn new words and speech sounds, the /s/ and /z/ sounds typically develop later than sounds such as /p/, /m/, and /b/. Interdental and dental lisps are common in young children, and many resolve naturally by about age four and a half.
Some signs suggest it's time to seek help. Lateral and palatal lisps are not considered typical developmental patterns and should be evaluated by a speech-language pathologist. You may want to seek help once your child is three, and if the lisp lingers past age five or frustrates your child, that is a clear reason to start.
Early support can make correction easier because speech patterns are often more flexible before they become established habits. A speech-language pathologist can determine whether a child is likely to outgrow a lisp or would benefit from targeted speech therapy.
Lisps in Adults
Many adults have a lisp that has been present since childhood. Some never received speech therapy, while others had treatment but continued to use the pattern over time. A lisp can also develop later in life when dental work, dentures, or orthodontic appliances such as Invisalign change the way the tongue moves inside the mouth.
The good news is that adults can successfully learn new speech patterns. Speech therapy for a lisp in adults focuses on finding the correct tongue placement, producing the sound accurately, and carrying that skill into everyday conversation. Many adults seek speech therapy to feel more confident during presentations, meetings, interviews, and social interactions.
Progress often takes longer for adults than for children because their speech patterns have been practiced for many years. Online speech therapy works well for lisp treatment because video feedback, screen sharing, and guided practice make tongue placement and self-monitoring easier to learn.
How Speech Therapy Helps Correct a Lisp
Speech therapy is the primary treatment for a lisp and can be effective for both children and adults. A speech-language pathologist begins with an evaluation to identify which sounds are affected and the factors contributing to the speech pattern. Treatment then focuses on teaching the correct tongue placement for clear /s/ and /z/ production.
Sessions often use visual and tactile cues. A mirror can help a person see tongue placement, while tools such as a straw may help direct airflow for a lateral lisp. For an interdental lisp, the focus is usually on moving the tongue behind the teeth and building a new speech habit through practice.
Some people benefit from additional support. Orofacial myofunctional therapy may help when tongue thrust contributes to the lisp by addressing resting tongue posture and swallowing patterns. A tongue tie may warrant an evaluation by an ENT or dentist, and bite or alignment issues may involve an orthodontist alongside speech therapy.
The timeline for improvement varies. Many children make steady gains over a few months, while an older child or adult often needs more time to fully correct a lisp because the speech pattern has been established for years.
In-Person and Online Speech Therapy
Both in-person and online sessions can effectively treat a lisp. Online speech therapy works especially well because screen sharing, a mirror, and recorded examples make tongue-placement issues easy to model and review from home.
At-Home Practice
Short, consistent practice at home builds sound faster than long, tiring sessions. Saying the /s/ and /z/ sounds on their own first, then in words and sentences, helps a child or an adult make a new /s/ sound a natural habit. Props like puppets can make those reps feel like play for a child.
Family Involvement
For a child, family support speeds progress. When a parent knows the target sound and offers gentle reminders during the day, the child practices far more often than in a session alone.
Fun Articulation Activities for Speech Therapy
Find out fun articulation activities for speech therapy in this blog.
Common Myths About Lisps
A few myths about lisps cause needless worry. The biggest one is that a lisp signals low intelligence, which is simply not true. A lisp is a speech impediment, not a sign of how smart a person is, and it has nothing to do with thinking or language skills.
Another mix-up involves the so-called Spanish lisp. The /th/ sound that some Spanish speakers use for /c/ and /z/ is a regional feature of the language, not a speech disorder, and it does not need to be corrected. A true lisp affects the /s/ and /z/ in a person's everyday talk, whatever language they speak.
What We See Working With Clients
Families rarely contact us asking whether a lisp is interdental or lateral. Parents are more likely to say their child avoids reading aloud at school because classmates comment on their speech. Adults often tell us they notice their lisp every time they introduce themselves in a meeting or speak up on a conference call.
One elementary school student came to us because teachers and classmates frequently asked them to repeat words with /s/ sounds. We noticed an interdental lisp and a tongue-thrust pattern at rest. As we worked on tongue posture and speech sound placement together, the child became easier to understand and grew more comfortable participating in class discussions.
An adult client sought help after orthodontic treatment changed how certain sounds felt during speech. They noticed a slushy quality on /s/ sounds and became increasingly self-conscious during virtual meetings. Through guided practice and video feedback, they learned to direct airflow through the center of the mouth and reported feeling less distracted by their speech during work conversations.
Clear/s/ and /z/sounds matter most outside the therapy session. The goal is to feel comfortable speaking during classroom discussions, work meetings, presentations, and everyday conversations. Treatment focuses on building speech patterns that hold up in real life.
Frequently Asked Questions About Lisps
1. What is the cause of a lateral lisp?
A lateral lisp comes from air slipping over the sides of the tongue. It is close to the right spot, but the sides sit too low, which gives the /s/ a wet, slushy sound. Unlike a frontal lisp, it is not a normal part of speech development.
2. What does a palatal lisp sound like?
A palatal lisp makes the /s/ and /z/ sounds more like /sh/. It happens when the middle of the tongue lifts toward the soft palate at the back of the mouth. Of the four types of lisps, it is the least common.
3. How can an interdental lisp be corrected?
An interdental lisp is corrected by moving the tongue behind the front teeth. A speech therapist uses visual cues, sometimes with a mirror, as well as verbal and tactile cues to help the child or adult feel the new placement. Steady practice then turns it into a habit.
4. At what age should a lisp be corrected?
Lateral and palatal lisps can be evaluated at any age because they are not part of typical speech development. Parents can seek help as early as age three. For an interdental lisp, many children outgrow the pattern, so speech therapy is often recommended if it persists beyond age five.
5. Is it too late to fix a lisp as an adult?
No, adults can learn to correct a lisp at any age. Speech therapy focuses on developing accurate tongue placement and building new speech habits. Progress often takes longer for adults than for children because the pattern has been established over many years.
6. Is a lisp a speech impediment or a speech disorder?
A lisp is a type of speech sound disorder. Many people also use the term "speech impediment" to describe a lisp because it affects speech clarity. Both terms are commonly used, though speech-language pathologists typically use the more specific term "speech sound disorder."
How Connected Speech Pathology Can Help
At Connected Speech Pathology, our speech-language pathologists help children, teenagers, and adults correct a lisp through online speech therapy. We begin with a careful evaluation, identify the type of lisp and its cause, and build a plan around the sounds and routines that fit each person. Sessions are virtual and shaped around real goals.
Summary
What is a lisp? In short, it is a common speech sound disorder that affects the /s/ and /z/ sounds, typically due to tongue placement during speech. The four main types of lisps, interdental, dental, lateral, and palatal, each involve a different tongue position, and a speech-language pathologist can identify which pattern is present.
Some lisps resolve as children develop, while others are more likely to benefit from speech therapy. Treatment focuses on building accurate tongue placement, developing consistent sound production, and carrying those skills into everyday conversation. Children and adults can make meaningful improvements with focused practice and guidance from a speech-language pathologist.
About the Author
Allison Geller 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, published research on aphasia, and leads a team of specialists helping clients improve skills in public speaking, vocal presence, accent clarity, articulation, language, fluency, and interpersonal communication.
