Sucking on the end of the thumb is a "phase" encountered by countless millions of American children. In fact, most parents regard it as simply a benign, if juvenile, part of the process of growing up. In some rare cases, however, sucking the thumb constitutes a problem to the child's developmental health.

What causes thumb sucking?

Children suck their thumb to accommodate a natural sucking instinct that commonly begins when they're still very small. Experts believe as many as 90% of all children will pass through the thumbsucking phase.

When does the phase stop?

Most children spontaneously stop sucking their thumbs around the age of five or six months. However, the sense of relaxation and security it affords can take some children months or even years longer to fully outgrow.

Older children suck their thumbs as a way to cope with feeling tired, restless, bored, sleepy, or when they experience other unpleasant feelings. In some cases, children suck their thumbs to provide comfort after a traumatic or unsettling event.

When should the thumb sucking stop?

As a guideline, children over the age of three years old should have already stopped sucking their thumb on a routine basis. Child psychologists have also found that once the thumb sucking continues past that point, it becomes harder to quit.

What damage comes from too much thumb-sucking?

Extended thumb sucking can lead to severe dental and jaw problems. Dentists believe thumb sucking often leads to a poor alignment of the upper and lower levels of teeth called malocclusion.

Thumb sucking is also shown to create speech impediments such as lisps and trouble pronouncing many consonant sounds.

How parents can help their kids break the habit.

Pulling the thumb out of the child's mouth will only encourage the habit when parents are not around. Instead, many child psychology professionals recommend distracting the child with conversation or encouraging them to make hand gestures.

Painting clear nail polish on the child's thumb works in some cases and not in others. Many times the child simply grows used to the polish's taste.

Finally, asking a trusted authority figure, such as a teacher or doctor, to encourage the child to break the habit is also successful.