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Thumb Sucking Research: How Old is Too Old?

Research Summary

Thumb sucking has long been a focus of clinical study. Early psychoanalysts posed a relationship between thumb sucking and later masturbatory behavior, linked by underlying psychopathology. However, time hasn’t proved this belief, and with little evidence to support this idea clinicians and researchers now believe it’s more appropriate to classify it as a simple habit instead of a psychological disorder. In most cases, thumb sucking is a natural product of early childhood with no real lasting implications on a child’s psychology. The DSM-IV, the psychology handbook for classifying mental conditions, has no diagnosis for for it or related behaviors, such as nail biting. As such, research is aimed on recognizing when thumb sucking becomes something more than a simple habit. For most children, this behavior ends around 4 years old as they develop more self-management skills. Thumb sucking deserves serious attention when the duration and/or the intensity extends beyond these boundaries.

Thumb Sucking Facts

Thumb sucking is normally a harmless product of child development. In fact, babies have been observed thumb sucking in the womb, suggesting that the behavior is biologically rooted.

However, research has found thumb sucking to be related to some serious conditions, also known as comorbidity. For example, several studies have been able to reduce chronic hair pulling (trichotillomania) through targeting thumb sucking behavior.

Conclusions made in a 1991 study estimated that 95% of newborns are observed thumb sucking. This statistic drops to approximately 50% in 2-4 year olds, and down to 25% in 5 year olds. Thumb sucking in school aged children ranges from 5.9% to 28%, according to estimates from three separate studies.

For the majority of children, thumb sucking begins in the first few months of life. Thumb sucking only becomes a serious concern when it is a chronic behavior that occurs in two or more settings (such as at home and at school) after the age of 5. Studies have found that females are also more likely to suck their thumbs throughout all ages.

Chronic thumb sucking does lead to some known negative medical and dental outcomes. Malocclusion (overbite/underbite), crossbite, increased overjet (upper teeth extend out of mouth), and anterior openbite (large gap between upper and lower teeth) are all problems that may not self-correct if chronic thumb sucking occurs beyond age 4. Hand to mouth behavior is also believed to be a primary cause of lead poisoning in children.

There are possible negative social outcomes of chronic thumb sucking. Some research has found that thumb sucking children may be looked down upon by their young peers. Research in 1993 found that first grade students viewed thumb sucking peers as less likable than their other peers.


As discussed in this article, thumb sucking behavior is most likely harmless. However, if your child falls into the problem categories discussed above then it’s advised that you seek help from a pediatrician.  If you see chronic issues developing it is extremely important to nip them in the bud before serious negative impacts occur. When your child continues to thumb suck after age 4, and does so in multiple settings, its time to talk to a professional.

Research Quality Indicators


The lead author is a professor in the Psychology Department at Eastern Michigan University.


Title: Practitioner’s Guide to Evidence-Based Psychotherapy

Publisher: Springer

Article Type: Article or Chapter in an Edited Book

Peer-Reviewed: No

Impact Factor: n/a


Study Design: n/a


Byrd, M. R., Nelson, E. M., & Manthey, L. M. (2006). Oral-digital habits of childhood: Thumb sucking. In Practitioner’s guide to evidence-based psychotherapy (pp. 718-725). Springer US.


By | 2017-08-27T22:59:36+00:00 March 28th, 2016|Health, Parenting|0 Comments

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