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 odour.
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.
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 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 odour
- hair protruding from the lesion
formation of more than one sinus tract, or holes in the skin