pilonidal sinus

What is pilonidal sinus

A pilonidal sinus is a small hole or tunnel in the skin at the top of the buttocks (natal cleft), where they divide. This is the cleft between the buttocks just below the base of the spine in the sacrococcygeal region. Pilonidal sinus disease is a chronic skin problem that it is characterized by one or more sinus tracts; these are cavities with a narrow opening on the skin surface (pilonidal sinus). In most cases, the cavity is filled with nests of hair – hence the name pilonidal (“pilus” meaning hair and “nidal” meaning nest). Hairs carry bacteria, which can cause inflammation and infection. A non-inflamed lump is known as a pilonidal cyst. If the pilonidal sinus becomes infected a pilonidal abscess may form or the pus can drain through a tunnel (sinus) out to your skin.

Pilonidal sinus doesn’t always cause symptoms and only needs to be treated if it becomes infected. An infection will cause pain and swelling.

Most people with a pilonidal sinus don’t notice it unless it becomes infected and causes symptoms. An infected pilonidal sinus is red, painful and may bleed or leak pus. These symptoms can develop quickly, often over a few days. They’re signs of pilonidal sinus infection and need treating.

See a doctor if you have a small lump at the top of your bottom (between your buttocks) that’s painful, red, bleeding or leaking pus.

Persistent, complex or recurrent pilonidal sinus disease must be treated surgically. Procedures vary from taking the roof off the sinuses to wide and deep excision (i.e. all affected areas are completely cut out). In all cases, the cavity is scrubbed and scraped out to remove hair and abnormally healing granulation tissue. Several techniques are available for wound healing and closure; these include:

  • Dressing or packing open wounds
  • Marsupialization (forming a pouch), which results in a smaller wound compared to wounds that are left open to granulate
  • Closure using skin flaps for wide excisions.

Figure 1. Pilonidal sinus

Pilonidal sinus home treatment

Washing your natal cleft every day may help to prevent an infection. Use of depilatory creams, laser or frequent shaving of the midline buttock region have all been shown to prevent recurrence of pilonidal sinus in those who have experienced a previous attack.

An occasional discharge can be treated with antibiotics.

It is sometimes possible to have a procedure to drain a pilonidal abscess.

Pilonidal sinus causes

It’s not clear what causes a pilonidal sinus.

Possible causes of pilonidal sinus include:

  • Some people are born with small holes or pits near the base of the spine. These are in fact enlarged hair follicles.
  • Follicular occlusion; some people are genetically prone to this. They may also suffer from hidradenitis suppurativa, acne conglobata and dissecting cellulitis (follicular occlusion syndrome or tetrad).
  • When subjected to friction and motion, the follicles are injured and disrupted so the hair pokes through the wall of the follicle into the surrounding skin setting up a foreign body reaction.
  • Neighboring hairs or free hairs from other parts of the body collect in the pit and invade the small opening created by the distorted hair follicles.
  • Skin and perineal bacteria such as Staphylococcus aureus and Bacteroides species invade the opening and cause infection.

A skin problem, pressure or friction may cause hair between the buttocks to be pushed inwards.

This may either be hair growing around the buttock area, or loose hair shed from the buttocks or elsewhere that gathers around the buttock cleft and enters the pilonidal sinus.

Pilonidal sinuses are more common in men because they tend to be hairier.

Sitting for long periods can also increase your chances of getting a pilonidal sinus.

Pilonidal sinus disease risk factors

Pilonidal sinus disease affects both men and women usually between the ages of 20–40 years. Pilonidal sinus disease is 2–3 times more common in men than women. Other factors that increase the risk of pilonidal sinus disease include:

  • Coarse, curly or crinkly hair
  • Obesity
  • Family predisposition
  • Poor hygiene
  • Prolonged sitting or buttock friction causing increased sweating
  • Repeated local injury (once known as “Jeep rider’s disease” as it hospitalized more than 80,000 US soldiers in WWII)
  • Co-existing hidradenitis suppurativa

Pilonidal sinus signs and symptoms

Signs and symptoms of pilonidal sinus can vary from a small painless pit or dimple at the base of the spine to a large painful abscess. Most patients have progressive tenderness, particularly after prolonged periods of sitting, such as during a long drive. Signs and symptoms include:

  • Pain, redness and swelling
  • Small hole or holes draining fluid that may be clear, cloudy or bloody
  • If infected, the draining pus may have a foul odor
  • Fever, malaise or nausea
  • Visible or lumpy tracts 2–5 cm long in chronic or recurrent pilonidal sinus disease

Pilonidal sinus diagnosis

The clinical features of pilonidal sinus is usually straightforward. If necessary, skin biopsy can be undertaken. The histopathological features of pilonidal sinus characteristically show foreign body reaction.

Pilonidal sinus treatment

Pilonidal sinus treatment without surgery

Pilonidal sinus treatment isn’t needed if there are no signs of infection. A “watch and wait” approach will be recommended.

It’s very important to keep the area between your buttocks clean by showering or bathing regularly. You should keep the area free of hair by shaving or using a hair removal agent every 2–3 weeks. The pilonidal cyst may resolve itself. Persistent and inflamed pilonidal cysts (acute pilonidal abscess) are incised (cut into) and drained out to reduce inflammation and pain. Occasionally the pilonidal abscess cavity may be cut out completely to remove hair nests and skin debris; this reduces the rate of recurrence to about 15%.

Treatment for an infected pilonidal sinus will depend on:

  • your symptoms
  • the size of the sinus
  • whether it’s your first sinus or a recurring problem

A pilonidal sinus abscess will need treatment with antibiotics. The pus inside will also probably need to be drained.

There are a number of treatment options for a recurring pilonidal sinus that’s painful, bleeding or leaking discharge. Your doctor will discuss these with you.

In most cases you’ll be offered painkillers, such as acetaminophen (paracetamol) and anti-inflammatories to help reduce pain and swelling.

Pilonidal sinus surgery

Surgery is indicated for recurrent pilonidal sinus and surgery is the most dependable way to remove the pilonidal sinus and pockets of infection. The surgery is performed under a general anesthetic and usually takes about 30 minutes. Your surgeon will remove the pilonidal sinus and infected tissue.

There are many operations for pilonidal sinus, indicating that none are 100% effective. Most have a success rate of greater than 90%, with wound breakdown occurring in up to 5-10% of cases. Excision of the pilonidal sinus with repair by Rhomboid flap is ideal for large pilonidal sinuses, with the lowest recurrence rate.

Figure 2. Pilonidal sinus surgery

Pilonidal sinus surgery

Minor operation to drain pus from sinus

Incision and drainage

Hospital procedure for an uncomplicated abscess. A small hole is made in the abscess so the pus can be drained.

  • general anesthetic or local anesthetic, depending on the size of the abscess
  • hospital stay: you can leave the same day
  • regular (daily) dressing changes
  • recovery time: 4 to 6 weeks

Surgery to remove sinus – wound left open

Wide excision and open healing

Surgery for a large or repeatedly infected sinus. The sinus is cut out and some surrounding skin removed. The wound is left open to heal naturally.

  • general anesthetic
  • hospital stay: you can usually leave the same day
  • regular (daily) dressing changes
  • lowest risk of sinus coming back
  • recovery time: 6 to 12 weeks

Surgery to remove sinus – wound closed

Excision and wound closure, often with flattening of the groove between the buttocks

Surgery for a large or repeatedly infected sinus. The sinus is removed and an oval-shaped flap of skin cut out on either side of it. The two sides are stitched together.

  • general anesthetic
  • hospital stay: you can usually leave the same day
  • stitches removed about 10 days after operation
  • quicker recovery time than wide excision and open healing
  • higher risk of infection (the wound may need to be opened and dressings changed regularly)

Plastic surgery is sometimes used if the area being treated is particularly large. The sinus is removed and the surrounding skin reconstructed.

Less invasive procedures, like injection with fibrin glue, are also available in some places.


You’ll have a follow-up appointment with your specialist after your surgery. This is usually about 6 weeks later but may be slightly longer.

Pilonidal sinus surgery complications

General complications

  • pain
  • bleeding
  • unsightly scarring
  • blood clots

Specific complications:

  • partial breakdown of your wound
  • slow healing
  • numbness around your wound.

Pilonidal sinus surgery recovery

You should be able to go home the same day after your surgery.

What to do after your operation:


  • keep the affected area clean
  • wear comfortable, loose-fitting cotton underwear
  • eat plenty of fiber to make going to the toilet easier and avoid straining


  • do not lift heavy objects or do strenuous exercise for the first week or so
  • do not ride a bike for 6 to 8 weeks
  • do not go swimming until your wound has completely healed

Pilonidal sinus surgery recovery time

How soon you can return to work depends on:

  • the procedure you had
  • how quickly you recover
  • the type of job you do

Most people are able to return to work within 2 weeks of surgery.

Your surgeon will be able to give you more advice about your recovery.

You should be able to return to work after 2 to 3 weeks.

Regular exercise should help you to return to normal activities as soon as possible. Before you start exercising, ask the healthcare team or your doctor for advice.

The pilonidal sinus can come back.