So, independent of suction or friction being the main force of hair movement inward, hair orientation plays a major role in smaller tracts. In larger-diameter sinus tracts, scale effects may be diminished because of reduced scale-to-wall contact surface. In a recent study, we examined the hair in the sinus.6 We found that more than two thirds of the hair in the sinus was without root. The average length of the <400 hair particles in the sinus was 0.9 ± 0.7 cm. We did not count the one side cut hair to both side cut hair, but it can be estimated that between half and two thirds of hair has been cut at both ends.6 Because of the missing root and the small diameter differences in short cut hair fragments, we often could not tell the orientation of distal and proximal hair ends.7
Hair of larger diameter and larger axial strength is most likely to exert larger scale effects, promoting forced hair insertion. Because most hairs are sharp cut on both sides, the initial injection into the skin surface is possible on both sides. However, only the now-rootless proximal side (root first) will be the ruthless one and will be propelled much deeper and faster. Drs. Gosselink and Ctercteko can be congratulated. They add another important piece to the puzzle that fits convincingly into the pathomechanism of pilonidal sinus.