Trichotillomania (hair-pulling disorder) is characterized by the persistent and excessive pulling of one’s own hair, resulting in noticeable hair loss. [1, 2, 3, 4] Hair pulling can occur in any area of the body where hair grows. The scalp is the most common area, followed by the eyelashes and eyebrows.  The alopecia that results from hair pulling can range from small undetectable areas of hair loss to total baldness.
Trichotillomania is 7 times as prevalent in children as in adults, with the peak prevalence between the ages of 4 and 17 years.  It can cause a child to experience distress and may result in moderate impairment in social or academic functioning.  Additionally, trichotillomania may result in impairment in other important areas of functioning, such as family relationships.
Far more articles on trichotillomania are found in behavioral and psychiatric journals than in dermatologic journals. However, dermatologists are more likely to see these patients before psychiatrists, and the number of trichotillomania patients seen in dermatologic clinics seems to be far greater than the number seen in psychiatric clinics.
Regardless of its pathogenesis, trichotillomania is a kind of alopecia that must be differentiated from other kinds of alopecia (eg, alopecia areata, traction alopecia, androgenetic alopecia, alopecia mucinosa) and is diagnosed primarily by behavioral and mental health providers and psychologists. Physicians and dermatologists are also professionals involved in the diagnosis of trichotillomania. Because earlier treatment yields a better prognosis and prevents complications such as trichobezoar, psychologists, physicians, and dermatologists all play an essential role in the diagnosis of trichotillomania. 
Diagnostic criteria (DSM-5)
The American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), places trichotillomania in the category of obsessive-compulsive and related disorders and notes that it is characterized by recurrent body-focused repetitive behavior (hair pulling) and repeated attempts to decrease or stop the behavior. The behavior can occur during both relaxed and stressful times, but there is often a mounting sense of tension before hair pulling occurs or when attempts are made to resist the behavior.
The specific DSM-5 criteria for trichotillomania (hair-pulling disorder) are as follows  :
Recurrent pulling out of one’s hair, resulting in hair loss
Repeated attempts to decrease or stop the hair-pulling behavior
The hair pulling causes clinically significant distress or impairment in social, occupational, or other important areas of functioning
The hair pulling or hair loss cannot be attributed to another medical condition (eg, a dermatologic condition)
The hair pulling cannot be better explained by the symptoms of another mental disorder (eg, attempts to improve a perceived defect or flaw in appearance, such as may be observed in body dysmorphic disorder)
From a dermatologic standpoint, trichotillomania is a form of traumatic alopecia. The trauma to the hair occurs as a result of the patient’s repetitive hair-pulling behavior. The hair pulling may be one of several phenomenologically related grooming behaviors, such as nail biting and skin picking.
Trichotillomania results in highly variable patterns of hair loss. The scalp is the most common area of hair pulling, followed by the eyebrows, eyelashes, pubic and perirectal areas, axillae, limbs, torso, and face. The resulting alopecia can range from thin unnoticeable areas of hair loss to total baldness in the area(s) being plucked.
In addition, trichophagia (ie, mouthing or ingesting hair) is common in persons who pull out their hair. This chewing or mouthing behavior can frequently lead to the formation of trichobezoars (ie, hair casts) in the stomach or small intestines. Trichobezoars can result in anemia, abdominal pain, hematemesis, nausea or vomiting, bowel obstruction, perforation, gastrointestinal (GI) bleeding, acute pancreatitis, and obstructive jaundice.
The etiology of trichotillomania is largely unknown, though both environmental and genetic causes have been suspected. Explanations that have been proposed for the onset and maintenance of the hair-pulling behavior include the following:
Coping mechanism for anxiety or stressful events
A benign habit that developed from a sensory event (eg, itchy eyelash) or another event and resulted in trichotillomania
Co-occurring with another habitual behavior (ie, thumbsucking) in young children 
Serotonin deficiency - A link may exist between a deficiency of the neurotransmitter serotonin (5-hydroxytryptamine [5-HT]) and trichotillomania; the hypothesized connection between the two is based on the success of selective serotonin reuptake inhibitors (SSRIs) in treating some people with trichotillomania
Structural brain abnormalities - Magnetic resonance imaging (MRI) studies have demonstrated that some individuals with trichotillomania have abnormalities of the lenticulate
Abnormal brain metabolism - Positron emission tomography (PET) scans have revealed that some individuals with trichotillomania have a high metabolic glucose rate in the global, bilateral, cerebellar, and right superior parietal areas
Genetic susceptibility - DSM-5 notes that there is some evidence that genetic vulnerability plays a role  ; trichotillomania occurs more frequently in people with obsessive-compulsive disorder (OCD) and their first-degree relatives
Disordered reward processing - Preliminary data suggest that trichotillomania may represent a disorder of altered reward processing within the central nervous system; a study by White et al regarding reward processing in trichotillomania patients demonstrated altered nucleus accumbens activations and a decreased functional connection between the dorsal anterior cingulate and nucleus accumbens and basolateral amygdala and reward network; input was through glutamatergic projections, identifying a possible intervention point with agents that modulate glutamate 
United States and international statistics
Although US epidemiologic studies on the prevalence of trichotillomania are rare, estimates indicate that approximately 8 million people have trichotillomania. The overall frequency is probably underestimated, because only persons who present for treatment are counted; denial of the disorder is frequent, and many individuals with the disorder do not seek professional intervention. Further epidemiologic studies are needed.
In a study of college students, approximately 1%-2% had past or current symptoms of trichotillomania.  The rate fell to 0.6% when patients were restricted to the group having related mental tension and relief; without such restrictions, the rate of hair pulling resulting in visible hair loss was 1.5% for males and 3.4% for females. A survey at an African American university (n=248) showed that 6.3% of those surveyed had a history of pulling out their hair. 
In the authors’ experience, the number of the patients with trichotillomania is approximately 5% of the number of patients with alopecia areata. The incidence of alopecia areata is approximately 50% of all patients with different alopecias, and the total number of hair loss patients approximately 2% of all dermatologic patients.
Age-, sex-, and race-related demographics
Trichotillomania is frequently a chronic disorder that lasts weeks to decades, with a variable age of onset. Hair-pulling sites may vary with the age of onset: Patients with a very early onset of trichotillomania are more likely to pull eyelashes, whereas those with a later onset are more likely to pull pubic hair.  In the study by Walther et all, it was reported that the 27 children in the preschool age group (0-5 y) only pulled from the scalp and over half of the 5- to 10-year-age group children pulled from other body areas in addition to the scalp. 
Although empirical data are not available, this condition appears to be substantially more common in children than in adults. In general, prognosis is related to patient age, as follows:
Children typically have a time-limited disorder, with an excellent prognosis
Adolescents have more severe disease, with a guarded prognosis
Adults, many of whom were diagnosed before reaching adulthood, have a poor prognosis
With regard to sex-related differences, the younger the patient, the more equal the sex distribution. However, a recent cross-sectional study of 110 young children (age 0-10 y) demonstrated that a female predominance still exists, even among younger patients.  In adult groups, most patients are women. In adolescents, girls are affected more often than boys. DSM-5 cites an overall female-to-male ratio of 10:1. 
No racial differences in prevalence have been reported; trichotillomania appears to be equally common in whites, blacks, and Asians.
In very young children, the prognosis is excellent; hair pulling that occurs in young children may be described more accurately as a short-term habit disorder. In late childhood and adolescence, the prognosis is usually good but should be considered guarded; the alopecia quite often continues for months or a couple of years and then recurs after a variable time. In adult patients, the prognosis is poor, and permanent recovery is uncommon.
Trichotillomania results in highly variable patterns of hair loss, ranging from small undetectable patches of hair loss to total baldness. Ingestion of the pulled hair can result in trichobezoar formation and subsequent anemia, abdominal pain, hematemesis, nausea or vomiting, bowel obstruction, perforation, GI bleeding, pancreatitis, and obstructive jaundice.
Trichotillomania can become a chronic and persistent condition of hair pulling. Specifically, symptoms of trichotillomania can persist for weeks to decades. Therefore, comprehensive treatment planning is critical and may require consultations with mental health professionals. Treating trichotillomania in children may be difficult because of the low reliability and validity of self-report.
Mortality is not reported with trichotillomania. Most patients with trichotillomania in dermatologic clinics are children and early adolescents. Patients may try to conceal the alopecic area and may have some restrictions in their school activities. In adult patients, trichotillomania may cause distress and impairment in occupational and social or marital relations. 
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