A lateral lisp is a speech pattern where air escapes over the sides of the tongue instead of flowing down the center, producing a “slushy” or “wet” quality on certain sounds. Unlike the more common frontal lisp, where the tongue pushes forward between the teeth, a lateral lisp involves sideways airflow that gives speech a distinctive mushy quality. It is not considered a normal part of speech development at any age, and it typically requires speech therapy to resolve.
How a Lateral Lisp Sounds
Parents and listeners often describe a lateral lisp as making speech sound “slushy,” “wet,” or “mushy.” The distortion happens because air is spilling out over the sides of the tongue and mixing with saliva in the cheeks, rather than being directed in a focused stream out the front of the mouth. The result is a heavy, imprecise quality that can make certain words hard to understand clearly.
A lateral lisp doesn’t just affect the “s” sound. It can distort a whole family of sounds that rely on the same central airflow pattern: /s/, /z/, “sh,” “ch,” “zh” (the middle sound in “beige”), and “j” (as in “judge”). All of these sounds require the tongue to form a narrow groove along its center to channel air forward. When the tongue sides drop or lose contact with the upper teeth, that channel collapses and the air takes the path of least resistance, spilling sideways.
How It Differs From a Frontal Lisp
The frontal (interdental) lisp is the one most people picture when they hear the word “lisp.” With a frontal lisp, the tongue pushes forward between the front teeth, turning an “s” into something closer to a “th” sound. Many children go through this as a perfectly normal phase and outgrow it by around kindergarten age. A frontal lisp that persists past that point can be corrected with therapy, but it’s not a red flag in a toddler.
A lateral lisp is different in both mechanism and developmental significance. The tongue is actually close to the correct position for an “s,” but the sides aren’t elevated enough to seal against the upper teeth. Air leaks laterally rather than streaming forward. This pattern is never a normal developmental stage. Children with lateral lisps do not typically outgrow them on their own.
There’s also a less common type called a dentalized (or addental) lisp, where the tongue presses against the back of the front teeth without poking through. This produces a muffled “s” rather than a slushy one. It’s a subtler distortion than either the frontal or lateral type.
What Causes a Lateral Lisp
There’s no single cause, but several structural and functional factors increase the likelihood. The tongue, jaw, teeth, and palate all work together to shape speech sounds, and disruption in any of these can contribute.
Dental alignment plays a role. Research published in the Journal of Applied Oral Science found that children with a posterior crossbite (where upper back teeth sit inside the lower back teeth) were about 1.8 times more likely to have speech distortion compared to children with typical alignment. Posterior crossbite was the only bite problem in that study linked to both altered tongue positioning and speech distortion. Anterior open bite, where the front teeth don’t overlap when the jaw is closed, was strongly associated with abnormal tongue posture (about 2.4 times more likely) but wasn’t directly linked to distorted speech on its own.
Breathing patterns matter too. Children who habitually breathe through the mouth or through a mix of mouth and nose were roughly 2.5 times more likely to have altered tongue positioning than nasal breathers. Chronic mouth breathing changes the resting posture of the tongue, which can carry over into how the tongue moves during speech.
In many cases, though, no obvious structural cause is found. Some children simply develop an incorrect motor pattern for directing airflow, essentially learning the wrong “route” for these sounds from the start. Because a lateral lisp is never part of typical development, early intervention tends to produce better outcomes than waiting.
How Speech Therapists Identify It
A speech-language pathologist listens for the characteristic wet or slushy quality and checks which sounds are affected. They’ll test sounds like “s,” “z,” “sh,” “ch,” and “j” in different positions within words: at the beginning, middle, and end. A child with a lateral lisp will typically show the distortion across all of these sounds and in all word positions, because the underlying problem is the same tongue posture for every one of them.
The therapist also looks at tongue placement directly, sometimes using a mirror or asking the child to hold their tongue in position while they observe. The key question is whether the sides of the tongue are making firm contact with the upper teeth and whether a central groove is forming along the midline. With a lateral lisp, the tongue edges tend to be “floppy,” allowing air to escape sideways instead of being funneled forward.
How Therapy Works
Correcting a lateral lisp means retraining the tongue to seal its edges against the teeth and direct air through a narrow central groove. One widely used approach is called the butterfly technique, named for the tongue shape it aims to create.
The method starts from a sound the child already makes correctly. Therapists first confirm that the child produces “t” and “d” normally, because those sounds place the tongue tip in roughly the right spot. Therapy generally isn’t attempted with children under four, since they need to be able to follow specific instructions about tongue placement.
Here’s the core idea: when you say “ee” as in “been” or the short “i” in “bin,” the sides of your tongue lift slightly and press against your upper teeth while a groove forms along the center. This is the “butterfly position,” with the raised tongue edges acting as wings and the central groove representing the butterfly’s body. The child learns to hold this shape and then direct a stream of air straight down that groove.
The therapist uses vivid, kid-friendly language to make the concept stick. “Wings up, pressed firmly against the teeth” keeps the air from leaking sideways. “Floppy wings let the air escape; strong wings keep it in.” The child practices “shooting” air straight forward through the groove. Once they can produce a clean airstream in isolation, therapy gradually moves the sound into syllables, then words, then sentences, and eventually into everyday conversation.
Therapists may also use physical tools to help a child feel where the air should go. Straws, for example, can give sensory feedback about central airflow. The child blows through a thin straw to experience what a focused, forward air stream feels like, then tries to recreate that sensation without the straw.
How Long Correction Takes
There’s no fixed timeline. Some children pick up the new tongue position quickly and spend most of therapy practicing it in increasingly complex speech contexts. Others need more time at the foundational stage, especially if the lateral pattern is deeply ingrained or if structural factors like a crossbite are contributing. In general, the earlier therapy begins after the pattern is identified, the fewer habits need to be unlearned.
Adults can also correct a lateral lisp through the same principles, though the process often takes longer because the motor pattern has been reinforced over many more years of speaking. The techniques are essentially the same: learning the correct tongue posture, practicing central airflow, and gradually transferring the new sound into spontaneous speech. Consistency with home practice between sessions makes a significant difference in how quickly progress sticks.