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Pilonidal sinus

Pilonidal sinus

A pilonidal sinus is a small cyst that occurs in the cleft, the top part of the buttocks. Usually, a pilonidal sinus consists of hair, debris and dirt. It can catch infections and cause severe pain. With infection, it can ooze pus, blood and have foul odor.


When the process begins, there might not be any noticeable symptom but for a small dimple near the top part of the buttocks. If it gets infected, the depression might turn into a cyst or an abscess. A cyst is a closed sac filled with fluid, whereas an abscess is a swollen and inflamed tissue where pus gets collected. If you have an infection, the symptoms are:

  • Low grade fever
  • Swelling of cyst
  • Pain while sitting or standing
  • Reddened and sore skin around the depression
  • Pus or blood oozing out from the depression
  • Foul odor in the sac
  • Hair protruding from the area
  • Holes in the skin
  • More sinus tracts over a period of time


Activities like sitting cause friction and prompt the growing hair in the buttocks, into going back into the skin. When hair retracts back to the skin, the body considers hair as foreign particles and launches an immune response against the hair. Because of this immunization process, a cyst gets formed around the hair. Although the root cause for pilonidal sinus has not been established for certain, the factors that contribute to it are:

  • Changing of hormones after puberty
  • Growth of hair
  • Friction from clothes
  • Spending a lot of time sitting


The ways to prevent pilonidal sinus are:

  • Maintaining cleanliness and hygiene
  • Staying fit and active
  • Avoiding sitting for long hours at a stretch