Trichotillomania
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Trichotillomania is characterized by recurrent pulling out of one's hair resulting in noticeable hair loss. The individual typically experiences an increasing sense of tension immediately before pulling out the hair or when attempting to resist the behavior, and he or she may experience pleasure, gratification, or relief when pulling out the hair. Hair pulling may occur in states of relaxation and distraction (e.g., when reading a book, driving, or watching television), but may also occur during stressful circumstances.

Common sites of hair pulling may include the scalp, eyebrows, eyelashes, pubic region, or any other region of the body in which hair may grow.
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References:

Treating trichotillomania: A meta-analysis of treatment effects and moderators for behavior therapy and serotonin reuptake inhibitors.
McGuire, Joseph F.; Ung, Danielle; Selles, Robert R.; Rahman, Omar; Lewin, Adam B.; Murphy, Tanya K.; Storch, Eric A.; Journal of Psychiatric Research, Vol 58, Nov, 2014 pp. 76-83. 

Early childhood trichotillomania: Initial considerations on phenomenology, treatment, and future directions.
Park, Jennifer M.; Rahman, Omar; Murphy, Tanya K.; Storch, Eric A.; Infant Mental Health Journal, Vol 33(2), Mar-Apr, 2012 pp. 163-172.