Evidence that supports the theory of the origin of pilonidal sinuses as acquired, can be summarised as follows: ● Interdigital pilonidal sinus is an occupational disease of hairdressers, the hair within the interdigital cleft or clefts being the customers’. Pilonidal sinuses of the axilla and umbilicus have also been reported. ● The age incidence of the appearance of pilonidal sinus (82% occur between the ages of 20 and 29 years) is at variance with the age of onset of congenital lesions. ● Hair follicles have almost never been demonstrated in the walls of the sinus. ● The hairs projecting from the sinus are dead hairs, with their pointed ends directed towards the blind end of the sinus. ● The disease mostly affects men, in particular hairy men. ● Recurrence is common, even though adequate excision of the track is carried out.