Thumb-sucking is a childhood habit that often begins before a child is even born and continues for several years afterward. It tends to bring a soothing effect to children, particularly during the first few months or years of life.

All babies are born with a sucking reflex, and thumb-sucking is a habit that grows out of this reflex. Habits are patterns of behavior that are repeated, often without the person realizing it. Like many other childhood habits – including fingernail-biting, nose-picking and hair-twirling – thumb-sucking appears to have a calming effect in some children. In particular, thumb-sucking is believed to have pleasant associations with feedings and the end of hunger. This may explain in part why some children find the habit so hard to break.

Some children may suck their thumbs purely for entertainment. Children who are older may return to sucking their thumb whenever they are under stress or experience other anxieties. Thumb-sucking in response to obsessive thoughts may be an indication that the child has obsessive-compulsive disorder.

The reason why the thumb is sought out more than other digits is a mystery. It appears that random movements by a fetus or infant simply cause the thumb to come into contact with the mouth more than the other fingers. However, some children do go on to suck other fingers, or even their entire fists.

Contrary to common belief, thumb-sucking usually does not harm the development of a child’s teeth or cause an overbite during the child’s first three years of life. In cases of premature birth, there is evidence that thumb-sucking actually helps a child gain weight and reduces a child’s crying.

Thumb-sucking tends to peak around age 2, and most children stop sucking their thumbs by 4 years of age. However, other children may continue to suck their thumbs when they are bored, stressed or otherwise upset.

In most cases, a parent’s best approach to a child’s thumb-sucking is to ignore it. Most children eventually outgrow the habit on their own. However, thumb-sucking can become a problem when it continues past the age of 4 years, especially after permanent teeth begin to come in around age 6. Teasing and peer pressure from friends or siblings eventually convinces many of these children to stop, but others cannot seem to break the habit. Some may quit during the day but still suck their thumbs at night or in private. Children who continue to suck their thumbs for longer periods of time are at risk of developing an overbite if they suck vigorously or press against the roof of the mouth (palate).

Some parents prefer that their child suck on a pacifier rather than sucking their thumbs. A pacifier is a rubber or plastic nipple or teething ring. Pacifiers can be useful tools for young children who have a desire to continue sucking beyond nursing or bottle-feeding.

Parents who use pacifiers should only use them when they are sure their baby is not hungry. Children who are hungry and who receive a pacifier may become upset, which can interfere with feedings. Parents know their children best and are urged to use their judgment about whether or not a child is hungry.

The chief advantage of pacifiers is that many children find it easier to give up the habit of sucking on a pacifier than they do quitting thumb-sucking. There is also some evidence that pacifiers may help prevent sudden infant death syndrome (SIDS).