Pilonidal Sinus

A pilonidal sinus (PNS) is a small hole or tunnel in the skin. It may fill with fluid or pus, causing the formation of a cyst or abscess. It occurs in the cleft at the top of the buttocks. A pilonidal cyst usually contains hair, dirt, and debris. It can cause severe pain and can often become infected. If it becomes infected, it may ooze pus and blood and have a foul odor.

  • A PNS is a condition that mostly affects men and is also common in young adults. It’s also more common in people who sit a lot, like cab drivers.
  • Pictures of pilonidal sinus

What are the causes of pilonidal sinus disease?

The exact cause of this condition isn’t known, but its cause is believed to be a combination of changing hormones (because it occurs after puberty), hair growth, and friction from clothes or from spending a long time sitting.

Activities that cause friction, like sitting, can force the hair growing in the area to burrow back under the skin. The body considers this hair foreign and launches an immune response against it, similar to how it would react when dealing with a splinter. This immune response forms the cyst around your hair. Sometimes a person may have multiple sinuses that connect under the skin.

Identifying a pilonidal sinus and recognizing signs of infection

You may not have any noticeable symptoms at first other than a small, dimple-like depression on the surface of your skin. However, once the depression becomes infected, it will quickly develop into a cyst (a closed sac filled with fluid) or an abscess (a swollen and inflamed tissue where pus collects).

The signs of an infection include:

  • pain when sitting or standing
  • swelling of the cyst
  • reddened, sore skin around the area
  • pus or blood draining from the abscess, causing a foul odor
  • hair protruding from the lesion
  • formation of more than one sinus tract, or holes in the skin
  • You may also experience a low-grade fever, but this is much less common.