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Pilonidal sinus

A pilonidal sinus is a small hole, tunnel or pit that develops at the top of the buttocks where they meet at the bottom of the coccyx (tailbone). This can cause an abscess called a pilonidal abcess also known as a pilonidal cyst.

The word 'sinus' is usually associated with the nasal cavity but it also describes features that can appear elsewhere on the body. As well as the buttocks, pilonidal sinus has been known to affect the gaps between fingers and the belly button, although this is very rare.

What is a pilonidal abscess?

If pilonidal sinus holes get infected they can turn into a pilonidal abscess (pilonidal cyst) that looks like a boil.

Illustration of pilonidal abscess

Pilonidal sinus symptoms

The symptoms of pilonidal sinus and pilonidal abscess include:

  • Boil-like lump
  • Tender lump
  • Pain
  • Swelling
  • Redness
  • Smelly pus
  • Bleeding
  • Fever.

Pilonidal sinus causes

It isn't clear why some people develop a pilonidal sinus, but abnormal hair growth is usually blamed.

Hairs may push into the skin, or hair follicles get blocked and eventually rupture.

Other factors may include:

  • Sitting for long periods, such as when driving
  • Tight clothing
  • Friction
  • Personal hygiene problems
  • Obesity
  • Being hairier than normal
  • Coarser, curlier body hair type
  • Injury.

During the Second World War pilonidal sinus was known as 'Jeep disease' or 'Jeep seat' due to the number of cases among people driving military vehicles.

How common are pilonidal sinuses?

Pilonidal sinuses are relatively rare and affect around 26 in 100,000 people in the UK every year.

They are more common in men than women and usually appear in the late teens and early 20s.

When to seek medical care

If you find a pilonidal sinus or abscess, or experience symptoms, seek medical advice.

Earlier diagnosis and treatment can help avoid further symptoms, infection and complications.

Diagnosis of pilonidal sinus

Pilonidal sinus will be diagnosed based on symptoms and a physical examination.

Self-care at home

A pilonidal sinus should be kept dry and clean, and the area around it should be kept hair-free by shaving or using suitable hair removing products.

If an abscess has developed, seek medical advice. To avoid spreading bacteria, don’t try to squeeze or burst this yourself .

Medical treatment

Antibiotics may be recommended if there is pus present but no abscess, but surgical treatment is usually needed for an abscess.

Surgical treatment includes:

Incision and drainage. Under general anaesthetic, doctors make an incision in the abscess and drain out the pus. This is usually done as a day-case procedure. The wound will be dressed and wound care instructions given with advice on when to get dressings changed and any follow-up appointments.

Excision. A surgeon will remove the area of skin around the pilonidal sinus. The gap may be left open until it heals over naturally (wide excision), closed with stitches (excision and primary closure) or sealed with special fibrin glue.

The risks and benefits of these surgical procedures will be explained before they go ahead. This will include recovery times, infection risk and the chances of another pilonidal sinus developing.

Wound care instructions will vary depending on the procedure carried out.

Instructions will be given to seek medical advice if there's more pain, pus, fever or other concerns after going home from surgery.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on August 23, 2016

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