Thumbsucking

Thumb sucking is a behavior found in humans, chimpanzees, and other primates. It usually involves placing the thumb into the mouth and rhythmically repeating sucking contact for a prolonged duration. It can also be accomplished with any piece of skin within reach (such as the big toe) and is considered to be soothing and therapeutic for the person.

At birth, babies will reflexively suck any object placed in its mouth; this is the sucking reflex responsible for breastfeeding. This reflex disappears at about four months of age; thumb sucking is not purely an instinctive behavior and therefore can last much longer. Moreover, ultrasound scans have revealed that thumb sucking can start before birth, as early as 15 weeks from conception; whether this behavior is voluntary or due to random movements of the fetus in the womb is not conclusively known.

Children suck on objects (including pacifiers) to soothe themselves; sucking is one of a baby’s natural reflexes and completely typical for babies and young children. As a child develops the habit, they will usually develop a "favorite" finger to suck on, in much the same way they develop a favorite hand to write with. It is not known if the preference for a hand to suck on affects handedness in any way, or vice versa.

Thumb sucking can start as early as 15 weeks of growth in the uterus or within months of being born. Prior to 12 weeks, the fetus has webbed digits. Most thumb-suckers stop gradually by the time they are five years old. Nevertheless, many older children will retain the habit, some into adulthood. Habitual thumb sucking in adults may be due to stereotypic movement disorder or another psychiatric disorder.

Dental problems
Thumb-sucking can cause problems for dental development. To prevent their children from sucking their thumbs some parents put hot sauce or bitter-tasting chemicals such as thiomersal on their child's hands — although this is not a procedure encouraged by the American Dental Association : or the Association of Pediatric Dentists. During the 1950s, parents could get a series of sharp prongs known as "hay-rakes" cemented to a child's teeth to discourage sucking.

Most children stop sucking on thumbs, pacifiers or other objects on their own between two and four years of age. No harm is done to their teeth or jaws until permanent teeth start to erupt. The only time it might cause concern is if it goes on beyond 6 to 8 years of age. At this time, it may affect the shape of the oral cavity or dentition.

Tips from the American Dental Association :
 * Praise children for not sucking, instead of scolding them when they do.
 * If a child is sucking their thumb when feeling insecure or needing comfort, focus instead on correcting the cause of the anxiety and provide comfort to your child.
 * If a child is sucking on their thumb because of boredom, try getting a child's attention with a fun activity.
 * Involve older children in the selection of a means to cease thumb sucking.
 * The pediatric dentist can offer encouragement to a child and explain what could happen to their teeth if they do not stop sucking.
 * Only if these tips are ineffective, remind the child of their habit by bandaging the thumb or putting a sock/glove on the hand at night.

Summary of Best Practices Recommendations:
 * American Academy of Pediatrics : Most children suck their thumbs or fingers at some time in their early life. The only time it might cause concern is if it goes on beyond 6 to 8 years of age or affects the shape of the child's mouth and the position of teeth.
 * American Dental Association : Children suck on objects as a natural reflex; however, during and after the eruption of the permanent teeth, such sucking may cause problems with the skeletal development of the mouth and alignment of the teeth.

Oral imprinting
Researcher Elsie Mobbs in her study Thumbsucking and Mammalian One-Teat Preference  writes: "The logical flaws in the current explanations of fixated thumbsucking are:
 * The need to suck: This does not explain why infants fixate on one sucking object, one digit out of ten, and will refuse replacement sucking objects.
 * Hunger: there is no nutrition in thumbs and thumbsucking will also occur after feeds.
 * It is necessary normal development: Margaret Mead, anthropologist, noted that in societies where babies have free access to the breast then thumbsucking does not occur.
 * It does no harm: Skin excoriation and facial malocclusions which occur are not uncommon problems resulting from thumbsucking, *
 * It occurs as part of learning: The emotional fixation on the one chosen sucking object, self-sucking, is mirrored across the mammalian spectrum if animals are human reared... The phenomenon of mammalian oral imprinting is a better explanation for thumbsucking."

Homeopathy
A hypothesis exists among homeopathic doctors which suggests that children who suck their thumbs are subconsciously working to strengthen the jaw, tongue and facial muscles. The muscles associated with the mouth are often underdeveloped at birth and possible benefits of thumb sucking may exist, including but not limited to increased nervous activity in the orbicularis oris (or smile) muscle and the flexibility of the pterygoid muscles. The latter must be relaxed in order to avoid biting the thumb, and without the ability to relax the pterygoids a person could develop jaw tension or might be improperly diagnosed with temporomandibular joint disorder. A documented strong correlation exists between those who are predisposed to but forced to stop sucking their thumb and those who need extensive orthodontia to straighten the teeth. Unfortunately, little data exists as to the long term benefits of thumb sucking primarily because few children are able to overcome the social stigmas associated with its practice.

Freudianism
Sigmund Freud considered thumb sucking a form of sexual expression and used it to study infantile sexuality. Passionate sucking can consume all of a child's attention, leading either to sleep or even in some cases to a motor reaction in a kind of orgasm. Furthermore, the rubbing of certain sensitive parts of the body (such as the genitals) is often combined with sucking. In 1919, in issue 20 of Neurologisches Zentralblatt Dr. Galant published the confession of a young woman who had not given up this activity as a child in which she described the satisfaction derived from it as analogous to sexual satisfaction.