CHAPTER 54

Thumb-sucking and Other Habits

Carol D. Berkowitz, MD, FAAP

Habits are defined as somewhat complicated, repetitive behaviors that become automatized, fixed, and carried out easily and effortlessly. They are different from tics, which are rapid, repetitive muscle twitches involving the head, face, or shoulders. Tics are also referred to as habit spasms (see Chapter 130). Children have many habits that are characteristically discouraged, such as thumb-sucking, nail-biting, skin picking, nose picking, hairpulling (trichotillomania), rocking, biting other children, and teeth grinding (bruxism). Some habits, such as pica (the ingestion of nonfood substances), are potentially harmful. Children engage in most of these habits because of their soothing potential. In recent years, cutting, a form of self-injury in adolescents, has received attention. While not a habit in a traditional sense, cutting is described by teenagers as a way of dealing with stress and alleviating anxiety. One-third of children use transitional objects for comfort. Blankets or favorite toys are traditional transitional objects that represent an age-appropriate coping strategy. Most transitional objects are stroked, and the stroking often occurs in association with thumb-sucking. Transitional objects sometimes present a problem because children experience distress if these objects are lost or misplaced or need cleaning.

Epidemiology

Thumb-sucking probably represents the most common habit of children and is also reported in other primates, including chimpanzees. Up to 90% of children engage in this habit at some point. Prenatal ultrasonography has demonstrated in utero thumb-sucking in some fetuses. The median age for the onset of hand sucking is 54 minutes after birth, and 90% of newborns show hand-sucking behavior by the age of 2 hours. Forty percent of children between the ages of 1 and 3 years, 33% of children between the ages of 3 and 5 years, and 25% of children at the age of 5 years still suck their thumbs. Some children suck fingers rather than thumbs. Other oral behavior may involve lip sucking, lip biting, and toe sucking. Lip sucking and biting begin at about 5 to 6 months of age and occur in about 90% of infants. It is unusual for these actions to persist as habits. Toe sucking is noted in infants who are 6 to 7 months of age and is reported in 80% of typically developing infants.

Trichotillomania is a disorder once believed to be uncommon but now thought to affect 8 million Americans (about 5 in 1,000). The term, first coined in 1889 by French dermatologist Hallopeau, is derived from the Greek thrix (hair), tillein (pull), and mania (mad-ness). The condition is an impulse control disorder in which alopecia develops from compulsive hairpulling. Hairpulling may involve hair from the head, eyebrows, eyelashes, or pubic area. Trichotillomania is reported from infancy into adulthood. In young children, boys and girls are equally affected, but in older children and adolescents, females outnumber males. In preschool-age children, trichotillomania is viewed as benign, similar to thumb-sucking. When the condition appears in older children (most common age of onset is between 9 and 13 years) the condition is more likely to persist into adulthood. The disorder is not associated with comorbid psychopathology, but there may be some association with mood disorders or attention-deficit/hyperactivity disorder. There is a condition in infants, called “baby trich,” in which infants pull their mother’s hair when they are being held or nursed. This is considered typical exploratory behavior.

Rhythmic movement habits are stereotypical, repetitive behaviors that usually occur in infants younger than 1 year. Based on parental reporting, rhythmic movements are noted in up to 15% to 20% of the population. Rhythmic movements include rocking (about 19% of infants), when infants rock back and forth; jouncing (5%– 10%), when they move in an up-and-down manner on their hands and knees so that the whole crib rocks; head rolling (8%); and head banging (5%). Rhythmic movements are seen more commonly in boys; the male to female ratio is 3:1. These habits usually occur with a frequency of 60 to 80 movements per minute, often when infants are tired, and last for less than 15 minutes before they fall asleep. In a recent study that used home videosomnography to assess the occurrence of sleep-related rhythmic movements in more than 700 infants and toddlers, the prevalence was significantly less, at only 2.87%.

Rhythmic movements have sometimes been referred to as sleep tics. These tics are reported in 20% of children, most often between the ages of 6 and 10 years. As a rule, tics are 3 times more common in boys than girls. They tend to be noted with increased frequency in children who are shy or overly self-conscious or have obsessive-compulsive tenden-cies. Tics usually occur when children are under stress.

Biting, an aggressive habit noted in toddlers, may be related to teething. It occurs more often in children with delayed language development.

Nail-biting (onychophagia) is deemed to be a sign of internal tension and affects 10% to 40% of children. Nail-biting begins between the ages of 3 and 6 years, and the peak age is 13 years. One-third of adolescents bite their nails, but 50% of these adolescents break the habit by the time they reach adulthood. When nail-biting persists into adulthood, it may be considered an oral compulsive disorder and classified under obsessive-compulsive and other disorders in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). The family history for nail-biting is often positive. Identical twins are concordant for the condition in 66% of cases. In contrast, the incidence in dizygotic twins is 34%.

Nose picking, noted in children and adults, is reported in more than 90% of individuals. In general, adults and older children limit nose picking to when they are unobserved, but younger children will pick their noses in public. There are no sex-based differences in the prevalence of nose picking. Nosebleeds are the most common complication of nose picking (see Chapter 90).

Pica is defined as the ingestion of nonfood, nonnutritive products. The peak prevalence of pica is between the ages of 1 and 3 years. The prevalence is increased in children of lower socioeconomic status, and the behavior occurs in 10% of children who present with lead poisoning. To meet the DSM-5 criteria, pica must persist for longer than 1 month at an age when eating such objects is developmentally inappropriate and not part of a culturally sanctioned practice. The word pica is derived from the Latin word for the magpie (picave), a bird attributed with eating anything. Patients with pica may prefer specific substances to ingest, such as ice (pagophagia), soil (geophagy), or stones (lithophagia).

Teeth grinding (bruxism) is reported in 5% to 15% of children and frequently occurs during sleep. Boys are more commonly affected than girls, and the disorder seems to regress later in life. It is reported with increased incidence among children with developmental delays, including those with autism spectrum disorder. The cause is unknown, although it may be associated with malocclusion in some children. There is some evidence that sleep bruxism in childhood is associated with an increased incidence of exposure to secondhand smoke. The disorder may contribute to temporoman-dibular joint dysfunction and pain.

Self-injury has been reported in up to 20% of adults with intellectual disabilities. Autism spectrum disorder and the absence of speech are the highest associated risk factors. Nail-biting, head banging, and self-biting are frequently described associated behaviors. Severe self-injury related to biting is seen in Lesch-Nyhan syndrome.

Clinical Presentation

Children with common habits, such as thumb-sucking or rhythmic movements, may be brought to the physician with these particular complaints because the parent wants advice about stopping the behavior. Other children may present with consequences of habits, such as alopecia (trichotillomania), paronychia (nail-biting), or lead intoxication (pica). Whitlow (infection of the tip of the finger; also called felon) and, rarely, osteomyelitis of the distal phalanx have also been reported with nail-biting. Osteomyelitis should be considered in a nail-biting child who presents with an abscess of the finger. Hairpulling can be associated with hair ingestion, also referred to as trichophagia. Trichobezoars that can complicate trichotillomania associated with trichophagia may present with gastric outlet or bowel obstruction. Symptoms then include abdominal pain, anorexia, early satiety, nausea, vomiting, halitosis, and weight loss (Box 54.1).

Pathophysiology

Children engage in habits to reduce stress and provide comfort. Thumb-sucking is related to nonnutritive sucking. Although the initial purpose of sucking is nutritional, the pleasure associated with sucking reinforces the behavior. Infants who are served from a cup from birth develop no interest in sucking. Humans and other primates spend more time in nonnutritive than in nutritive sucking. Monkeys use a 5-point hold, with 2 hands, 2 feet, and mouth (holding on to their mother’s nipple) for attachment. Universal thumb-sucking is noted even in orphan monkeys, and sucking is thought to be an important aspect of environmental adaptation. Nonnutritive sucking occurs even in the absence of fatigue, hunger, or discomfort and has a purpose in itself—to provide comfort and be self-soothing. The maximum intensity of sucking occurs at 7 months of age. For older children (≥3 years), sucking is also a way of coping with boredom.

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