Copyright © The American Society of Colon & Rectal Surgeons, Inc. Unauthorized reproduction of this article is prohibited. 1 DISEASES OF THE COLON & RECTUM VOLUME XX: XXX (2017) BACKGROUND: Pilonidal sinus disease is thought to be caused by intrusion of hair into healthy skin; loose hair in the intergluteal fold is thought to promote disease. However, compelling evidence to support these postulates is lacking; the cause of pilonidal sinus disease remains uncertain. OBJECTIVE: To determine whether particular properties of hair are associated with susceptibility to pilonidal sinus disease, we compared physical properties of hairs of patients with pilonidal sinus disease with hairs from control subjects who were matched for sex, BMI, and age. DESIGN: This was an experimental study with establishment of a mechanical strength test for single hairs to quantify the maximum vertical force that a hair could exert, following tests of strength of occipital, lumbar, and intergluteal hair. SETTINGS: Hair from patients with pilonidal sinus disease and matched control subjects were harvested from patients of the St. Marienhospital Vechta Department of Procto-Surgery. PATIENTS: A total of 17 adult patients with pilonidal sinus disease and 217 control subjects were included. MAIN OUTCOME MEASURES: ANOVA and intraclass and interclass variations of data gained from mechanical strength tests of occipital, lumbar, and intergluteal hair were included. RESULTS: Vertical hair strength was significantly greater in patients with pilonidal sinus disease. Occipital hair exhibited 20% greater, glabella sacralis 1.1 times greater, and intergluteal hair 2 times greater strength in patients with pilonidal sinus disease than in matched control subjects (all p = 0.0001). In addition, patients with pilonidal sinus disease presented with significantly more hair at the glabella sacralis and in the intergluteal fold. LIMITATIONS: The study was limited by its relatively small number of patients from a specific cohort of European patients. CONCLUSIONS: Occipital hair exhibited considerable vertical strength. Because occipital hair exerted the greatest force and cut hair fragments were found in the pilonidal nest in large quantities, these data suggest that pilonidal sinus disease is promoted by occipital hair (see Video Abstract, http://links.lww.com/DCR/A329). KEY WORDS: Hair; Karydakis; Pilonidal sinus; Scalp; Vertical strength. D ifferent theories regarding the etiology of pilo- nidal sinus disease (PSD) have been postulated. Although familial clustering of pilonidal disease is common, hereditary factors have not been identified. 1 Bascom 2 and others argued that midline pits occurred as a Strength of Occipital Hair as an Explanation for Pilonidal Sinus Disease Caused by Intruding Hair Dietrich Doll, M.D., Ph.D. 1,7 ฀•฀Friederike D. Bosche, M.D. 1 ฀•฀ Verena K. Stauffer , M.D. 2 Inga Sinicina, M.D., Ph.D. 3 ฀•฀Sebastian Hoffmann, M.D., Ph.D. 4 Dominic van der Zypen, Ph.D. 5 ฀•฀Markus M. Luedi, M.D., M.B.A. 6 1 Department of Procto-Surgery, St. Marienhospital Vechta, Academic Teaching Hospital of the Medizinische Hochschule Hannover, Vechta, Germany 2 Department of Surgery, Luzerner Kantonsspital Sursee, Sursee, Switzerland 3 Institute of Forensic Medicine, Technical University Munich, Munich, Germany 4 Marien-Krankenhaus Bergisch Gladbach, Bergisch Gladbach, Germany 5 Swiss Federal Office of Social Insurance, Bern, Switzerland 6 Department of Anesthesiology and Pain Therapy, Bern University Hospital Inselspital, University of Bern, Bern, Switzerland 7 Department of Surgery, Medical School, University of the Witwatersrand, Johannesburg, Soweto, South Africa Dis Colon Rectum 2017; XX: 00–00 DOI: 10.1097/DCR.0000000000000795 © The ASCRS 2017 Supplemental digital content is available for this article. Direct URL ci- tations appear in the printed text, and links to the digital files are pro- vided in the HTML and PDF versions of this article on the journal’s Web site (www.dcrjournal.com). Financial Disclosure: None reported. Correspondence: Dietrich Doll, M.D., Ph.D., Department of Procto- Surgery, St. Marienhospital Vechta, Academic Teaching Hospital of the Hannover University, Marienstr 6–8, D-49377 Vechta, Germany. E-mail: ddoll@gmx.de LWW 02/3/17 4 Color Fig(s): F1-4 16:55 Art: DCR-D-16-00724 <zjs;ORIGINAL CONTRIBUTION> • <zjXXX> • <zdoi;10.1097/DCR.0000000000000795> ORIGINAL CONTRIBUTION