Can thumb sucking cause a lisp?

The need for sucking usually disappears by 12 months of age.
The need for sucking usually disappears by 12 months of age.  Photo: Shutterstock

Sucking is a natural reflex in the newborn. It is very normal for some babies to suck their thumbs, fingers or a pacifier to soothe and comfort them. Sucking may also help them to fall asleep. This natural reflex begins to diminish around six months of age - the same time they usually start solids. 

The need for sucking usually disappears by 12 months of age. However, for many reasons some toddlers and children may continue to suck their thumbs beyond this age.

Thumb sucking, if stopped in the early years, will not have a significant effect on the development of the oral muscles (lips, tongue, cheeks), on the teeth or on speech development. Prolonged, persistent thumb sucking beyond four years of age may cause the teeth to become misaligned.

Pressure created by the thumb in the front part of the mouth may cause a "maloclussion" where the top and bottom front teeth cannot meet properly. There may be a gap called an open bite. This gap is where the tongue is able to protrude forward in speech, causing an interdental lisp.

An open bite can be corrected if the child stops sucking their thumb. Once the thumb is removed from the mouth the teeth are able to grow normally and eventually this gap will close. Once this gap closes the tongue will have a barrier to stop it coming forward.

The age of the child is very important in determining whether the thumb sucking is causing a problem with speech. There are two types of lisps, an interdental lisp and a lateral lisp.

A lateral lisp is where the air is released out of the sides of the tongue rather than through the middle.  When the child says the sounds /s, z ,ch, j/  they appear distorted and "slushy". This type of lisp is not normal at any age and you should see a speech pathologist as soon as possible.

An interdental lisp is an articulation (speech) difficulty where the tongue protrudes forward between the front teeth. When saying sounds such as /s/ and /z/ it may be produced as a 'th' sound. If a child has an interdental lisp the tongue may also protrude forward for other sounds such as /l, t, d, n, sh, ch, j/. All children develop certain sounds at particular ages. It is very normal for a child even up to 4.5 years of age to talk with an interdental lisp even if they do not suck their thumbs.

There are many reasons why children develop a lisp in their speech. Thumb sucking may be a risk factor but we cannot say for certain that all children who suck their thumbs will develop an interdental lisp.  There is still controversy over the implications of thumb sucking so parents need to be cautious of the advice they may receive.  


Prolonged and persistent thumb sucking can also cause the tongue to constantly move forward and backwards in the mouth, thereby creating a tongue thrust swallow pattern. This swallow pattern should disappear by 12 months of age. If a child is sucking their thumb for a prolonged period of time this tongue thrust swallow pattern can affect their ability to swallow efficiently. This can also effect dentition as well as speech.

The effect of thumb sucking is also dependent on the frequency and duration during the day. Therefore, the more a child sucks their thumb, the greater the impact on dentition, oral muscles and speech. It is recommended that your child removes anything from their mouth when they are talking as this will encourage normal speech patterns.

In my clinical experience I have seen children who were and are still sucking their thumbs and have a lisp. The need for treatment will depend on their age and the type of lisp. 

It is highly recommended that parents seek advice regarding prolonged thumb sucking from an experienced health professional. This may be your General Practitioner, Dentist or Speech Pathologist. The Speech Pathologist is trained to assess speech difficulties and ascertain the causative factors.  It is very important to seek professional opinion as early as possible.

Thumb sucking is one risk factor associated with speech difficulties. Prolonged, persistent thumb sucking may affect dentition, oral musculature and speech.

Find a health practitioner near you with Healthshare and Melissa Compton's (Paediatric Speech Pathologist at Westmead Doctors) profile here.