The Hair in the Sinus: Sharp-Ended Rootless Head Hair Fragments can be Found in Large Amounts in Pilonidal Sinus...

Hair has been identified as the causative agent of Pilonidal Sinus Disease (PSD). Stiffer, dark hair as well as hairiness has been postulated as causative factors. Astonishingly, despite the early clinical significance of this condition (Hodges in Boston Med Surg J 2:485-486, 1880), macroscopic and microscopic examinations of hair inside pilonidal sinus cavities have been scarce. The purpose of this study was to study the morphological aspects of the hair found in PSD in order to determine the origin of the hair.

Hair from inside pilonidal sinus cavities was collected intraoperatively from 20 PSD patients. Additionally, occipital, lumbar and intergluteal hair was harvested from the same patients and compared to the hair of volunteer-matched pair patients admitted to the hospital at the same time for non-PSD surgery. Intra- and intergroup variations of hair length were characterized with analysis of variance. Numbers and lengths of pilonidal sinus nest hair were recorded. Hair was examined clinically and with light and scanning electron microscopy using surface enhancing gold and carbon dust coating techniques.

Analysis of 624 pilonidal sinus nest hair samples from 20 independent sinus cavities revealed that hair within pilonidal sinus nests is rootless in 74%. Shorter hair was found inside the pilonidal sinus compared to other sites (length 0.9 ± 0.7 cm p < 0.0001). Furthermore, hair found inside of the sinus was significantly shorter than hair protruding from pores (p < 0.000). Hair samples show razor sharp but no broken or split ends. On electron microscopy, these spiky hair ends resemble cut hair ends. Pilonidal hair nests contained between 1 and over 400 hair fragments.

Short hair fragments with rootless sharp cut ends were found within pilonidal sinus cavities. Morphologically, these fragments resemble short cut rather than intact body hair. Since short cut hair, e.g., derived from the head potentially enters the pilonidal cavity more easily than longer hair, the source of these cut hair fragments needs to be eliminated when aiming to prevent Pilonidal Sinus Disease.