Unlocking the Thumb-sucking mystery: A dive into the neurochemistry of non-nutritive sucking
Thumb-sucking is a common childhood habit that typically begins in infancy as a natural reflex for self-soothing. However, when this behaviour persists beyond the age of four, it can raise concerns among parents and caregivers. Prolonged thumb-sucking can result in a number of structural changes that impact a child’s health, swallowing and speech. Understanding the underlying reasons why some children continue to suck their thumbs can provide valuable insights for intervention strategies. In this blog post, we will explore the origins of thumb-sucking and delve into the intricate role of neurotransmitters like dopamine, serotonin and endorphins in sustaining this behaviour.
Typical sucking development 
Firstly, let’s examine why infants start sucking in the first place. Babies are born with a rooting and sucking reflex. The rooting reflex is seen when the corner of the baby’s mouth is stroked or touched. The baby will turn his/her head and open his/her mouth to follow and root in the direction of the stroking. This helps the baby find the breast or bottle to start feeding. This reflex lasts about 4 months. The sucking reflex is seen when the roof of the baby’s mouth is touched which causes the baby to start sucking. This reflex develops between 32-36 weeks gestation. Because babies also have a hand-to-mouth reflex that goes with rooting and sucking, they often suck on their fingers or hands. Babies find comfort and security in the rhythmic sucking motion, which helps regulate their emotions and provides a sense of familiarity. As children grow, most naturally outgrow this habit as they develop alternative coping mechanisms and self-regulation skills.
However, for some children, thumb-sucking persists well into the primary school years and beyond. Understanding the neurochemical factors contributing to this behaviour can shed light on why certain children find prolonged comfort in thumb- and finger-sucking.
The Role of Dopamine
Dopamine often referred to as the “feel-good” neurotransmitter, plays a crucial role in reward and pleasure pathways within the brain. When a child sucks their thumb, the repetitive motion triggers the release of dopamine, creating a pleasurable sensation. This positive reinforcement strengthens the association between thumb- or finger-sucking and a sense of comfort or satisfaction. In children who continue to suck their thumbs past the age of four, there may be a heightened sensitivity or reliance on the dopamine release associated with this habit.
The Influence of Serotonin
Serotonin, another neurotransmitter, is closely linked to mood regulation and emotional well-being. Thumb-sucking can act as a self-soothing mechanism that temporarily boosts serotonin levels, providing a sense of calm and relaxation. Children who struggle with emotional regulation may turn to thumb-sucking as a means of stabilising their mood.
Endorphins and Stress Reduction
Endorphins, often associated with pain relief and stress reduction, play a role in reinforcing habits that provide a sense of comfort. Thumb-sucking, particularly during stressful or anxiety-inducing situations, may trigger the release of endorphins, helping the child cope with overwhelming emotions.
Addressing Emotional Needs
Speech pathologists can collaborate with other healthcare professionals to explore strategies that support the development of emotional regulation skills and self-soothing in children who excessively engage in thumb-sucking. As a child develops these other skills, they won’t need to rely on the non-nutritive sucking as much and this behaviour will be easier to address. It’s important to consider why a child may be relying on thumb-sucking, as removing the child’s primary coping mechanism before supporting them to develop other ways of self-soothing, will only make the situation even more stressful.
In conclusion, by understanding the role of neurotransmitters like dopamine, serotonin and endorphins in sustaining non-nutritive sucking behaviours, we have a deeper understanding of why some children continue with this behaviour beyond the age of 4. We need to collaborate with parents, caregivers and other professionals to address the underlying emotional needs of the child, as well as to understand other physiological reasons why a child relies on finger- or thumb-sucking. This holistic approach aims to support the child’s overall development, fostering healthier habits and prevent long term impacts on the oral structures.
