Pilonidal Sinus

A pilonidal sinus is an infected tract under the skin between the buttocks. Treatment commonly involves an operation.


Incidence of pilonidal disease is about 26 per 100,000 population. Pilonidal disease occurs predominantly in males, at a ratio of about 3-4:1. It occurs predominantly in white patients, typically in the late teens to early twenties, decreasing after age 25 and rarely occurs after age 45. One publication listed local irritation to the sacrococcygeal site, positive family history of pilonidal disease, sedentary life style, and obesity as occurring in notable percentages of patients with pilonidal sinus (all factors between 34-50% occurrence in pilonidal sinus). This condition used to be called ‘jeep disease, as it was common in army jeep drivers during World War II. This was probably a result of many hours driving and ‘bouncing’ on a hard seat, which caused irritation, minor injury and pressure around the natal cleft.

What is a pilonidal sinus?

  • Pilonidal means a ‘nest of hairs’.
  • A sinus tract is a narrow tunnel (a small abnormal channel) in the body. A sinus tract typically goes between a focus of infection in deeper tissues to the skin surface. This means that the tract may discharge pus from time to time on to the skin.

A pilonidal sinus is a sinus tract which commonly contains hairs. It occurs under the skin between the buttocks (the natal cleft) a short distance above the back passage (anus). The sinus track goes in a vertical direction between the buttocks. Rarely, a pilonidal sinus occurs in other sites of the body.

Pilonidal Sinus

Causation of Pilonidal Sinus

Patey and Scarf hypothesized the origin of pilonidal disease was acquired by penetration of hair into the subcutaneous tissue with consequent granulomatous reaction, basing this theory on the high incidence of recurrence, as well as occurrence of disease in other areas of the body, such as the hands of a barber or sheep shearer. Other authors have followed this emphasis of hair as disease origin, and, in fact, an acquired aetiology of the disease is now the prevailing theory in the medical world.

Therefore three pieces are instrumental in producing pilonidal sinus:

  • The invader, hair;
  • The force, causing hair penetration; and
  • The vulnerability of the skin.

Symptoms of pilonidal sinus

A pilonidal sinus may not cause any symptoms at first. You may not be aware that you have one. Some people notice a painless lump at first in the affected area when washing. However, in most cases, symptoms develop at some stage and can be ‘acute’ or ‘chronic’.

Rapid-onset (acute) Symptoms

You may develop increasing pain and swelling over a number of days as a ball of pus with surrounding skin infection (an infected abscess) develops in and around the sinus. This can become very painful and tender.

Persistent (chronic) Symptoms

Around 4 in 10 people have a recurrence of their pilonidal sinus. You may develop some pain which is less intense than the acute symptoms. Usually the sinus discharges some pus. This releases the pressure and so the pain tends to ease off and not become severe. However, the infection never clears completely. This can mean that the symptoms of pain and discharge can last long-term, or flare up from time to time, until the sinus is treated by an operation.


If you have no symptoms

If you have no symptoms then you will normally be advised to clear the affected area of hairs (by shaving, etc) and to keep the area clean with good personal hygiene.

If you have rapid-onset (acute) symptoms

If you have an infection then you may be treated with short period of antibiotics. Painkillers including anti-inflammatory may be very helpful to improve the pain. It may be that you need to have an emergency operation to puncture (incise) and drain the ball of pus with surrounding skin infection (abscess). This is usually done in hospital.

If you have persistent (chronic) symptoms

In most cases, an operation will be advised. There are various operations which are done to cure this problem. Your surgeon will be able to give the details and the pros and cons of each operation. The options include the following:

Wide Excision and Healing by Secondary Intention: This operation involves cutting out (excision of) the sinus but also cutting out a wide margin of skin which surrounds the sinus. The wound is not closed but just left open to heal by natural healing processes (healing by ‘secondary intention’). This usually requires several weeks of regular dressing changes until it heals fully. The advantage of this method is that all inflamed tissue is removed and the chance of the condition coming back (recurrence) is low.

Excision and Primary Closure: This means taking out the section of skin which contains the sinus. This is done by cutting out an oval-shaped (ellipse) flap of skin either side of the sinus, which takes out the sinus, and stitching together the two sides of the ellipse. The advantage for this is, if successful, the wound heals quite quickly. The risk of a recurrence or of developing a wound infection after the operation is higher than the above procedure. This risk may be reduced by using a wound technique in which the line of stitches was moved away from between the buttocks.

Incision and Drainage of Acute Pilonidal Abscess

Incision and Drainage of Acute Pilonidal Abscess: This requires in an emergency situation. Simple incision and drainage will evacuate the pus and therefore pressure which relieves patient’s symptoms of pain and swelling. The cavity is packed with keltostat (sea weed dressing) for the next few days until it is fully healed. A definite procedure later may be required to excised the pilonidal sinus

After any operation

Your surgeon will usually advise that the wound should be kept clean and any hair growing near it be shaved or removed by other means. Some surgeons recommend that, even when the wound is healed, you should keep the area free of hair growing by shaving every few weeks, or by other methods to remove the hair. This reduces the chance of the problem coming back (recurring)