Trichotillomania is defined as a self-induced and recurrent loss of hair.  It includes the criterion of an increasing sense of tension before pulling the hair and gratification or relief when pulling the hair.  However, some people with trichotillomania do not endorse the inclusion of “rising tension and subsequent pleasure, gratification, or relief” as part of the criteria; because many individuals with trichotillomania may not realize they are pulling their hair, patients presenting for diagnosis may deny the criteria for tension prior to hair pulling or a sense of gratification after hair is pulled. 3] Trichotillomania may lie on the obsessive–compulsive spectrum, also encompassing obsessive–compulsive disorder, nail biting (onychophagia) and skin picking (dermatillomania), tic disorders and eating disorders.
These conditions may share clinical features, genetic contributions, and possibly treatment response; however, differences between trichotillomania and OCD are present in symptoms, neural function and cognitive profile. 1] In the sense that it is associated with irresistible urges to perform unwanted repetitive behavior, trichotillomania is akin to some of these conditions, and rates of trichotillomania among relatives of OCD patients is higher than expected by chance.  However, differences between the disorder and OCD have been noted, including: differing peak ages at onset, rates of comorbidity, gender differences, and neural dysfunction and cognitive profile. 
When it occurs in early childhood, it can be regarded as a distinct clinical entity. 1] Because trichotillomania can be present in multiple age groups, it is helpful in terms of prognosis and treatment to approach three distinct subgroups by age: preschool age children, preadolescents to young adults, and adults.  Trichotillomania is often not a focused act, but rather hair pulling occurs in a “trance-like” state; hence, trichotillomania is subdivided into “automatic” versus “focused” hair pulling.  Children are more often in the automatic, or unconscious, subtype and may not consciously remember pulling their hair.
Other individuals may have focused, or conscious, rituals associated with hair pulling, including seeking specific types of hairs to pull, pulling until the hair feels “just right”, or pulling in response to a specific sensation.  Knowledge of the subtype is helpful in determining treatment strategies.  Signs and symptoms Trichotillomania is usually confined to one or two sites, but can involve multiple sites. The scalp is the most common pulling site, followed by the eyebrows, eyelashes, face, arms, and legs.  Some less common areas include the pubic area, underarms, beard, and chest. 5] The classic presentation is the “Friar Tuck” form of vertex and crown alopecia.  Children are less likely to pull from areas other than the scalp.  People who suffer from trichotillomania often pull only one hair at a time and these hair pull episodes can last for hours at a time. Trichotillomania can go into relapse-like states where the individual may not experience the urge to “pull” for days, weeks, months, and even years.  Individuals with trichotillomania exhibit hair of differing lengths; some are broken hairs with blunt ends, some new growth with tapered ends, some broken mid-shaft, or some uneven stubble.
Scaling on the scalp is not present, overall hair density is normal, and a hair pull test is negative (the hair does not pull out easily). Hair is often pulled out leaving an unusual shape. Individuals with trichotillomania may be secretive or shameful of the hair pulling behavior.  An additional psychological effect can be low self-esteem, often associated with being shunned by peers and the fear of socializing due to appearance and negative attention they may receive. Some people with trichotillomania wear hats, wigs, false eyelashes, eyebrow pencil, or style their hair in an effort to avoid such attention.
There seems to be a strong stress-related component. In low-stress environments, some exhibit no symptoms (known as “pulling”) whatsoever. This “pulling” often resumes upon leaving this environment.  Some individuals with trichotillomania may feel they are the only person with this problem due to low rates of reporting.  Other medical complications include infection, permanent loss of hair, repetitive stress injury, carpal tunnel syndrome, and gastrointestinal obstruction as a result of trichophagia. 1] In trichophagia, people with trichotillomania also ingest the hair that they pull; in extreme (and rare) cases this can lead to a hair ball (trichobezoar).
Rapunzel syndrome, an extreme form of trichobezoar in which the “tail” of the hair ball extends into the intestines, can be fatal if misdiagnosed.  Environment is a large factor which affects hair pulling.  Sedentary activities such as being in a relaxed environment are conducive to hair pulling.  A common example of a sedentary activity promoting hair ulling is lying in a bed while trying to rest or fall asleep.  An extreme example of automatic trichotillomania is found when some patients have been observed to pull their hair out while asleep.  This is called sleep-isolated trichotillomania.  Causes and pathophysiology Anxiety, depression and obsessive–compulsive disorder are more frequently encountered in people with trichotillomania.  Trichotillomania has a high overlap with post traumatic stress disorder, and some cases of trichotillomania may be triggered by stress.
Another school of thought emphasizes hair pulling as addictive or positively reinforcing as it is associated with rising tension beforehand and relief afterward.  A neurocognitive model — the notion that the basal ganglia plays a role in habit formation and that the frontal lobes are critical for normally suppressing or inhibiting such habits —sees trichotillomania as a habit disorder.  Abnormalities in the caudate nucleus are noted in OCD, but there is no evidence to support that these abnormalities can also be linked to trichotillomania.  One study has shown that individuals with trichotillomania have decreased cerebellar volume. 1] These findings suggest some differences between OCD and trichotillomania.  There is a lack of structural MRI studies on trichotillomania.  In several MRI studies that have been conducted, it has been found that people with trichotillomania have more gray matter in their brains than those who do not suffer from the disorder.  It is likely that multiple genes confer vulnerability to trichotillomania.  One study identified mutations in the SLITRK1 gene, another identified differences in the serotonin 2A receptor genes, and mice with a mutation on the HOXB8 gene showed abnormal behaviors including hair pulling.
These data are preliminary, but could indicate a genetic component in trichotillomania.  The more research that surrounds this relatively newly understood phenomenon, the closer that experts come to determining whether or not it is indeed gene linked.  Diagnosis and screening Patients may be ashamed or actively attempt to disguise their symptoms. This can make diagnosis difficult as symptoms are not always immediately obvious, or have been deliberately hidden to avoid disclosure.  If the patient dmits to hair pulling, diagnosis is not difficult; if patients deny hair pulling, a differential diagnosis must be pursued.  The differential diagnosis will include evaluation for alopecia areata, tinea capitis, traction alopecia, and loose anagen syndrome.  In trichotillomania, a hair pull test is negative.  A biopsy can be performed and may be helpful; it reveals traumatized hair follicles with perifollicular hemorrhage, fragmented hair in the dermis, empty follicles, and deformed hair shafts (trichomalacia). Multiple catagen hairs are typically seen.
An alternative technique to biopsy, particularly for children, is to shave a part of the involved area and observe for regrowth of normal hairs.  Treatment Treatment is based on a person’s age. Most pre-school age children outgrow it if the condition is managed conservatively. In young adults, establishing the diagnosis and raising awareness of the condition is an important reassurance for the family and patient. Non-pharmacological interventions, including behavior modification programs, may be considered; referrals to psychologists or psychiatrists are considered when other interventions fail.
When trichotillomania begins in adulthood, it is often associated with other psychiatric disorders, and referral to a psychologist or psychiatrist for evaluation or treatment is considered best. The hair pulling may resolve when other conditions are treated.  Psychosocial Habit Reversal Training (HRT) has the highest rate of success in treating trichotillomania.  HRT has been shown to be a successful adjunct to medication as a way to treat trichotillomania.  With HRT, doctors train the individual to learn to recognize their impulse to pull and also teach them to redirect this impulse.
In comparisons of behavioral versus pharmacologic treatment, cognitive behavioral therapy (including HRT) have shown significant improvement over medication alone.  It has also proven effective in treating children.  Biofeedback, cognitive-behavioral methods, and hypnosis may improve symptoms.  Medication Medications can be used to treat trichotillomania. Treatment with clomipramine (Anafranil), a tricyclic antidepressant, was shown in a small double-blind study to significantly improve symptoms, but results of other studies on clomipramine for treating trichotillomania have been inconsistent. 3] Fluoxetine (Prozac) and other selective serotonin reuptake inhibitors (SSRIs) have limited usefulness in treating trichotillomania, and can often have significant side effects.  Behavioral therapy has proven more effective when compared to fluoxetine or control groups.  Dual treatment (behavioral therapy and medication) may provide an advantage in some cases, but robust evidence from high-quality studies is lacking.  Acetylcysteine treatment stemmed from an understanding of glutamate’s role in regulation of impulse control.  Many medications, depending on individuality, may increase hair pulling.