How related are hair pulling disorder (trichotillomania) and skin picking disorder? A review of evidence for comorbidity, similarities and shared etiology.

Hair pulling disorder (HPD; trichotillomania) and skin picking disorder (SPD) are relatively common and potentially severe psychiatric conditions that have received limited empirical attention. Researchers are increasingly recognizing the similarities and co-occurrence of HPD and SPD, and several authors have suggested that the two disorders should be categorized together in the DSM-5. In the present article, we critically examined the evidence for comorbidity of HPD and SPD, and reviewed a diverse literature pertaining to shared risk factors and similarities in clinical characteristics. Evidence suggests that the two disorders co-occur more often than can be expected by chance, have substantial similarities in a variety of clinical characteristics (e.g., symptom presentation and course of illness) and may have some distal risk factors in common (e.g., genetic vulnerabilities). Implications for classification in the DSM-5, clinical management and research on etiology were discussed.