What Causes a Lisp? Learning, Tongue, Teeth, Hearing and the Evidence

✓ Reviewed against ASHA Practice Portal: Speech Sound Disorders, ASHA Practice Portal: Orofacial Myofunctional Disorders, AAPD Policy on Pacifiers, nidirect (NI government health information)Evidence level BLast reviewed October 23, 2026Published October 23, 2026

A lisp often has no single known cause. S and Z are learned later than many other sounds (90% of U.S. children have them by 4;0–4;11), so an S error is often the sound still developing. Tongue posture, bite and hearing are linked to some lisps. Evidence for tongue-tie and pacifiers is weak.

The short answer: usually no single cause

For many children, there is no single cause to find. ASHA divides speech sound disorders, the group that includes S distortions, into organic disorders, which have an identifiable underlying cause, and idiopathic disorders, which have no known cause. For idiopathic disorders, researchers look for risk factors instead.¹

Those risk factors apply to speech sound disorders in general, not to lisps specifically. They are being male, problems before or around birth such as preterm birth or low birthweight, a parent or sibling with speech or language difficulties, and long-lasting middle-ear fluid, often with hearing loss.¹

Organic speech sound disorders come from a motor or neurological condition, a structural difference such as cleft palate, or a sensory problem such as hearing loss.¹

The explanations people search for, and how strong the evidence is for each.
Possible factor	What the evidence shows	Strength of evidence
Still learning a hard sound	S and Z are learned late: 90% of U.S. children produce them correctly by 4;0–4;11	Strong (large review)
Tongue posture and tongue thrust	Linked to interdental (frontal) lisps, but the data show correlation, not proven cause	Moderate
Bite (crossbite, open bite)	Associated with speech distortion, including on S, in observational studies	Moderate (association only)
Hearing loss	A recognized cause of speech sound disorders	Strong for speech sound disorders in general
Tongue-tie	Systematic reviews find no clear causal link with speech	Weak and disputed
Pacifiers and thumb-sucking	Most speech outcomes are not linked; heavy or prolonged use may matter	Weak and inconsistent
Family history	A risk factor for speech sound disorders in general, not lisps specifically	Limited

The explanations people search for, and how strong the evidence is for each.^{3,2,5,1,8,9,12,13}

Causes of speech sound disorders: the full picture of risk factors

The most common explanation: S is a hard sound to learn

A 2020 review of U.S. children's consonant acquisition pooled 15 studies of 18,907 children. Using a 90% criterion, it found that /s/ and /z/ were acquired by 4;0–4;11, and all fricatives, the sound family that includes S and Z, by 6;11.^3,4

Fricatives are among the hardest English sounds. The same review cites earlier work grouping them with affricates as the most complex English consonants to articulate. It also reports that /s/ was one of the two consonants whose age of acquisition varied most across the studies.³

S errors are a normal part of learning the sound. In a reanalysis of 997 children aged 3 to 9, the most common errors on S at the start of a word were saying [t] or [d], dentalization, lateralization, and producing the sound further back, toward "sh." For many preschoolers, an S that comes out wrong is the sound still coming in, not a sign that something caused it.³

Not every child finishes learning the sound on their own. An estimated 3.6% of 8-year-olds have a persistent speech sound disorder, and 1%–2% of young adults have residual or persistent speech errors. These figures come from different studies, so they can't be read as a recovery rate.¹

Lisp in children: the patterns and when each is a concern

Tongue posture, tongue thrust and tongue-tie

Tongue thrust and resting tongue posture

ASHA lists distorted S and Z, "often with an interdental lisp," among the signs of orofacial myofunctional disorders. These are atypical movement patterns of the mouth and face muscles that affect where the tongue rests and how it moves during swallowing, breathing and speech.²

ASHA says these disorders come from a mix of learned behaviors, structural differences, and genetic and environmental factors. Children with speech sound disorders are more likely to show tongue thrust, but ASHA stresses that the evidence shows correlation, not causation. Estimates of how common a tongue-thrust swallow is in school-aged children range from 5.4% to 62.3%, so no single figure is reliable.²

ASHA names several factors that may play a role in these disorders. These include a blocked nasal airway from enlarged tonsils, adenoids or allergies, sucking or chewing habits that continue past age 3, and losing upper front teeth early. Chronic mouth breathing affects an estimated 10.1%–15.9% of children, and in one study about 31% of children with chronic mouth breathing had a speech sound disorder.²

Tongue-tie: weak and disputed evidence

Tongue-tie is often blamed for a lisp, but the evidence is weak. ASHA says the research trends toward minimal or no impact on speech, and that the effect of releasing a tongue-tie on speech errors is debated.²

A 2013 systematic review of 20 studies found no significant data suggesting tongue-tie causes articulation problems, and no definitive speech improvements after division. A 2022 review of 16 mostly small studies, with an average quality score of 3.88 out of 7, found no clear link between tongue-tie and speech disorders. A 2025 review found that publications on tongue-tie have risen sharply without a matching rise in evidence that settles the debates.^8,9,10

The field is genuinely divided. ASHA cites one study that linked tongue-tie severity to speech sound disorders. Small case series also give unstable results: in one series of five children, distortions fell after surgery but then rose from 8 to 11 by one to two years later. ASHA describes release as a case-by-case medical decision.^2,11

Can a lisp be caused by teeth?

Bite differences are associated with speech distortion. In a study of 547 Brazilian children aged 7 to 13, posterior crossbite was linked to speech distortion, judged on fricatives such as S and on sounds made with the tongue against the teeth (prevalence ratio 1.77, 95% CI 1.09–2.88). A deep overbite appeared protective (prevalence ratio 0.41), and an anterior open bite, where the front teeth don't meet, was linked to an altered tongue position.⁵

An acoustic study of 150 adults with severe bite and jaw differences found that their sibilants, the hissing sounds such as S, differed measurably from those of controls.⁷

These studies show an association, not proof that teeth cause a lisp. Many people with bite differences have a clear S, and many children with a lisp have typical teeth.^5,7

Changing the bite can change the S. A 2026 study of 67 people aged 15 to 36 with a Class III bite (underbite), compared with 54 controls, found that speech distortion, including on S, improved after corrective jaw surgery.⁶

Treating the teeth may not be the whole answer. ASHA notes that an orthodontist may need to treat a child's open bite before a speech-language pathologist works on a tongue thrust or an interdental lisp, and that an incorrect resting posture of the tongue can keep getting in the way of new sounds unless it is addressed. Speech-language pathologists don't diagnose malocclusion; they refer to a dentist or orthodontist.²

Hearing, pacifiers and thumb-sucking, and family history

Hearing

Hearing loss is a recognized sensory cause of speech sound disorders, and long-lasting middle-ear fluid has been associated with poorer speech development. ASHA includes a hearing screening in a full speech sound assessment.¹

Pacifiers and thumb-sucking: limited evidence

The American Academy of Pediatric Dentistry describes the evidence linking pacifiers to speech problems as limited. It finds no strong speech-related reason to avoid them, though it notes that several hours of daily use may matter for atypical errors.¹³

A 2021 study found that most speech outcomes were not significantly linked to pacifier use. The exception was more atypical errors with daytime use. A 2024 mini-review leans toward possible concern with use after age 3, but calls the evidence far from conclusive.^12,14

ASHA lists sucking habits that continue past age 3 as one factor that may play a role in orofacial myofunctional (tongue-posture) disorders. None of this supports blaming parents: ASHA describes a whole group of childhood speech sound disorders, called idiopathic, as having no known cause.^2,1,13

Is a lisp genetic?

A parent or sibling with speech or language difficulties is a risk factor for speech sound disorders in general. ASHA also names genetic factors among the contributors to tongue-posture disorders. The sources we reviewed did not identify a gene for a lisp itself, and we found no twin or heritability data specific to lisps.^1,2

Causes differ by type of lisp

Different lisp patterns don't share the same explanations. The evidence is clearest for the frontal (interdental) lisp and thin for every other pattern.^2,15

What the sources link to each S pattern. Thin evidence is labeled as thin.
Pattern	Factors linked in the evidence	How strong
Frontal (interdental)	Forward tongue rest posture, tongue thrust, open bite, early loss of upper front teeth	Moderate; correlation, not proven cause
Dentalized	One of the most common word-initial S errors among children aged 3–9	Describes how common it is, not why it happens
Lateral	No clear structural cause in the sources; one case report treated it as a movement-based (motor) error	Weak (single case report)
Palatal and whistling S	No reliable source found on cause or how common they are	Nothing to report

What the sources link to each S pattern. Thin evidence is labeled as thin.^2,5,3,15

The lateral lisp, a wet or "slushy" S, is where sources disagree. ASHA uses "a lateral /s/" as its example of a distortion that signals a speech sound disorder. However, a large reanalysis of children aged 3 to 9 listed lateralization among the common S errors. Because the sources disagree on how typical it is, a wet or slushy S is worth having checked by a speech-language pathologist rather than waiting.^1,3

A new lisp in an adult is a medical question

If speech changes suddenly, call 911

If speech suddenly becomes slurred, strange or difficult, call emergency services right away: 911 in the U.S., 999 in the UK, 000 in Australia or 112 in the EU. Sudden difficulty speaking can be a sign of a stroke.¹⁶

A lisp an adult has had since childhood is a speech error that has persisted. About 1%–2% of young adults still have residual or persistent speech errors.¹

If a lisp appears after a change to the teeth or jaw, a dentist or orthodontist is a sensible first stop. Bite and jaw differences are linked to measurable differences in sibilants, and in one study speech distortion improved after corrective jaw surgery.^7,6

A gradual speech change with no dental explanation needs a doctor's review. An NHS trust lists stroke, head injury, multiple sclerosis and Parkinson's disease among the causes of the nerve damage behind dysarthria, a motor speech disorder.¹⁷

Sudden slurred or changed speech: call emergency services now.
S changed after new braces, a retainer, dentures or other dental work: talk to your dentist or orthodontist first.
Unexplained speech change that comes on gradually: see your doctor.
Long-standing lisp you'd like to work on: a speech-language pathologist can assess it at any age.

What to do next

Finding out what is contributing to a particular lisp takes an in-person assessment. A speech-language pathologist's assessment can include checks of mouth structure, bite, tongue posture and hearing.^1,2

Child under 5: S and Z are still being learned. Model the words clearly, and don't make your child repeat them over and over.
Frequent ear infections or other hearing concerns: ask for a hearing check.
Open bite, crossbite or other bite concerns: see a dentist or orthodontist.
Tongue-tie: release is a medical decision made case by case. Ask for a speech assessment first.

🩺

See a licensed speech-language pathologist if S errors continue past the early school years, if the S sounds wet, slushy or mushy at any age, if speech is hard to understand, if your child is upset or teased, or if there are feeding, drooling or mouth-breathing concerns. You can find one through /find-support.

If you'd like a starting point at home, the free lisp check below listens to your child's S and Z for a few minutes. It is a preliminary screen only. It can't tell you what caused a lisp or what type it is, and it doesn't replace an assessment.

Free Lisp Test

A quick listening check of how your child's S sounds right now: a preliminary screen to help you decide on next steps, not a diagnosis or an answer about what caused it.

Try it free →

Start daily practice at home — free

Guided practice runs in your browser with a free parent account. SpeechStep is practice, not therapy: if your child may need a therapist, your country’s register of licensed professionals is the place to start.

Start free practice →Where to find a licensed therapist

Frequently asked questions

What causes a lisp?＋

Often no single cause can be found. ASHA calls speech sound disorders with no known cause idiopathic, and notes they are typically identified in childhood. S and Z are also learned later than many other sounds. Some lisps are linked to tongue posture, bite differences or hearing, and a speech-language pathologist can look at which factors might apply.

Can a lisp be caused by teeth?＋

Bite differences are associated with speech distortion, including on sounds like S. In one study of 7- to 13-year-olds, a posterior crossbite came with about 1.8 times the prevalence of speech distortion. That shows a link, not proof of cause, and treating the bite doesn't guarantee the lisp will go away: ASHA notes that tongue resting habits can still get in the way of new sounds.

Is a lisp genetic?＋

No study we reviewed identifies a gene for a lisp. A family history of speech or language difficulty is a risk factor for speech sound disorders in general, and ASHA lists genetic factors among the contributors to tongue-posture disorders. So family history can play a part, but it isn't the whole story.

Does tongue-tie cause a lisp, and will cutting it help?＋

The evidence is weak and disputed. Systematic reviews find no clear causal link between tongue-tie and speech, and no definitive speech improvement after release, although at least one study has found a link with severity. Release is a medical decision made case by case, ideally after a speech assessment.

Do pacifiers or thumb-sucking cause a lisp?＋

The evidence is limited and inconsistent. The American Academy of Pediatric Dentistry finds no strong speech-related reason to avoid pacifiers, though several hours of daily use may matter for atypical errors. ASHA lists sucking habits that continue past age 3 as one factor that may play a role in orofacial myofunctional disorders, which include a forward tongue resting posture.

Why have I suddenly got a lisp as an adult?＋

If speech suddenly becomes slurred or strange, call 911 (999 in the UK), because it can be a sign of a stroke. If the change followed new braces, a retainer, dentures or other dental work, start with your dentist or orthodontist. Any other unexplained speech change should be reviewed by a doctor.

Did I cause my child's lisp?＋

The evidence doesn't support blaming parents. ASHA describes a whole group of childhood speech sound disorders as having no known cause, and the research on pacifiers is weak. S is simply a hard sound that some children are still learning until about age 5.

Can an app tell me what's causing a lisp?＋

No. Working out what contributes to a lisp needs an assessment by a speech-language pathologist, which can include checks of mouth structure, bite and hearing. SpeechStep offers practice and a preliminary listening screen only. It doesn't diagnose or identify a cause.