Pilonidal sinus (hair cyst)
A pilonidal sinus is a small channel in the cleft at the top of the buttocks, near the tailbone, that sometimes becomes infected. This page explains the symptoms, that not everyone needs an operation, and what the treatments and aftercare are.
What is a pilonidal sinus?
A pilonidal sinus is a small hole or channel under the skin in the cleft between the buttocks, near the tailbone. Many people do not notice it until it becomes infected. ASCRS calls it a chronic skin disease in this area and says it is more common in men, usually between puberty and age 40, and that being overweight and having thick, stiff hair raise the risk.
Symptoms
- A small dimple or pit at the top of the cleft
- Suddenly a painful, red, swollen lump that makes sitting hard (an abscess)
- Clear, cloudy or bloody discharge; with infection, foul-smelling pus and sometimes fever, nausea and feeling unwell
ASCRS says most patients first come with an acute abscess. After that, many develop a sinus, a cavity under the skin that connects to the surface through one or more openings.
Who needs an operation?
Not everyone. If there are no symptoms and no infection, the NHS says no treatment is needed, only care and regular washing. If you have an abscess or repeated infections, treatment is needed. Exactly which method depends on the size of the sinus, the symptoms, and whether it is the first time or a repeat (NHS).
Treatment options
1. Care and pain relief
Wash the area regularly and use simple pain relief such as paracetamol or ibuprofen. Do not shave without a doctor’s advice (NHS).
2. Draining an abscess
If you have an abscess, the pus is usually drained through a small cut, sometimes under local anesthesia in the office or on the same day. Antibiotics and daily dressings may be needed. ASCRS also says drainage is usually done in the office under local anesthesia.
3. Surgery (for a chronic or recurrent sinus)
The sources name these options:
- Wide excision with an open wound: the channel and a little of the surrounding skin are removed and the wound heals from the base by itself. The NHS says it has the lowest chance of recurrence but needs regular dressings.
- Excision with the wound closed, or a flap: the edges are stitched. Healing is faster but the risk of infection is higher and the wound sometimes has to be reopened. Stitches come out after about 10 days (NHS).
- Unroofing: opening the roof of the channel, for complex or repeated infections, without removing it completely.
- Endoscopic method: a thin camera is used to remove hair and infected tissue and clean the channel without a large cut. The NHS says it has few complications and healing takes about a month, sometimes less.
- Reconstructive surgery (for a very large lesion) and, in some centers, fibrin glue (NHS).
Which method suits you or is available is explained by the surgeon after an examination.
After treatment
According to the NHS:
- Keep the area clean and dry and wear loose cotton underwear
- Eat enough fiber so you do not strain
- Avoid heavy lifting and strenuous exercise for about the first week
- No cycling for 6 to 8 weeks; do not swim until fully healed
- Most people return to work within about 2 weeks (depending on the operation and job)
- A follow-up visit is usually about 6 weeks later
ASCRS says a closed wound should be kept clean, dry and hair-free, and an open wound is dressed or packed so that drainage can come out and it heals from the base. See also the guide “Wound care and warm sitz baths”.
Risks
- Wound infection and a closed wound opening
- Recurrence. ASCRS says it can be chronic and recurrent; no source gives a definite figure
- Long healing time with an open-wound excision
When to call
- A painful, hot lump at the top of the buttock cleft with discharge or blood (the NHS says to book soon)
- After an operation: fever, increasing redness and swelling, a bad smell or pus, stitches opening, severe pain
- A lot of fluid or blood from the wound
A high fever with chills and feeling very unwell means you should be seen the same day or call 115 (Iran’s emergency number). Every patient’s treatment plan is different; ask your doctor about your own situation.
Frequently asked questions
Is this caused by poor hygiene?
No. The exact cause is not clear. The sources say hairs growing in the buttock cleft, or collecting there from outside, may push under the skin and cause irritation and infection. Pressure, friction and long periods of sitting raise the risk. Anyone can get it and it is not the patient's fault.
Does a sinus without infection need an operation?
According to the NHS, if there are no signs of infection no treatment is needed and "watchful waiting" is usually advised, with regular washing and no shaving unless a doctor says so. ASCRS says some sinuses heal without intervention, but most need a small operation. The decision is made by the doctor after an examination.
Does removing or shaving the hair help?
The sources do not agree. ASCRS treats keeping hair away (hair removal cream, shaving or laser) as the main long-term measure, and writes every 2 to 3 weeks until about age 30. The NHS advises not to shave the area without a doctor's advice. Ask your own doctor before doing anything.
Does it come back after an operation?
It can. The disease can be chronic and recurrent. The NHS says wide excision with an open wound has the lowest chance of recurrence but takes longer to heal and needs regular dressings; closing the wound heals faster but carries a higher risk of infection and of the wound opening. The NHS and ASCRS do not give a recurrence percentage. ASCRS says after about age 30 the hair is softer and the cleft shallower.
When can I cycle or go back to work?
The NHS says to avoid heavy lifting and strenuous exercise for about a week, no cycling for 6 to 8 weeks, and most people return to work within about 2 weeks. These periods depend on the operation and your job; the surgeon will set your own times.