Thumb sucking is a natural behavior that can be seen in most babies. It's the result of a normal drive that compels newborns to suck in order to get milk from their mothers' breasts. In fact, it isn't uncommon for thumb sucking to begin in the womb. Some babies do it only occasionally and stop at a young age, while others continue into early childhood. Adult thumb sucking is less common, and it usually happens because the natural habit was never broken.
The reasons for adult thumb sucking vary, but most do it simply out of habit. Because they didn't stop as children, the behavior became more ingrained over time. These individuals tend to report that they get a strong sense of calmness and a soothing effect from sucking their thumbs. It is often used as a coping mechanism for stress, occurring more frequently during difficult periods of life. They may also use it as a sort of natural sleep aid. Like other similar habits, it can be triggered by certain places or things. A small percentage of adult thumb sucking is related to the effects of a serious psychiatric illness.
There are no serious medical concerns associated with thumb sucking until a child reaches six to eight years of age. This is when permanent teeth begin to come in. The habit can potentially lead to dental malformations such as a cross bite or buck teeth, and these problems may range from mild to very severe. However, many people who continue sucking their thumbs into adulthood experience no related dental problems. Whether they occur is dependent on how much pressure there is on the teeth during sucking as well as how long and how often it's done. There's also an increased risk of illness associated with thumb sucking, unless hands are washed frequently.
Because it gives them a positive feeling and can usually be done in privacy, many individuals don't have a desire to stop thumb sucking. However, others do decide to quit, sometimes because they find that the behavior lowers their self-esteem. Cognitive behavioral therapy and a special dental device can help those who are having trouble giving it up. If the thumb sucking is related to underlying anxiety issues, psychiatric drugs may be prescribed.