A lisp is a speech impediment that specifically relates to making the sounds associated with the letters S and Z. It occurs when children do not quite get the tongue and lips in the correct place while they are learning to say the /s/ and /z/ sounds. There are four types of lisps: frontal, lateral, palatal, and dental. The most common type is the frontal lisp, which occurs when the tongue is pushed too far forward, making a "th" sound when trying to say words with S or Z in them. A lateral lisp is where the middle of the tongue hits the palate instead of the tongue tip touching just behind the teeth when the /s/ and /z/ sounds are pronounced. A palatal lisp is where the speaker attempts to make a sibilant while the middle of the tongue is in contact with the soft palate, or with a posterior articulation of the sibilant. A dental lisp is where the tongue protrudes between the front teeth when producing the /s/ and /z/ sounds.

Lisps usually develop during childhood and often go away on their own. However, some children may need professional help if they are still lisping after the age of 4 1/2. Speech-language pathologists are specialists who can help children with lisps. They will evaluate what type of lisp your child has and then help them with it over a period of time. It can take anywhere from a few months to a few years to get rid of a lisp. Successful treatments have shown that causes are functional rather than physical: that is, most lisps are caused by errors in tongue placement or density of the tongue within the mouth rather than caused by any injury or congenital or acquired deformity to the mouth.