Pain When You Sit and Repeated Infection Near the Tailbone: Is It Pilonidal Sinus?

Written by Dr. Ashutosh A Shah, M.B.B.S., M.S., M.Ch., D.N.B., Board Certified Plastic and Reconstructive Surgeon, Elegance Clinic, Surat. Reg. no. [REG NO]. 22+ years in reconstructive surgery. Qualifications and certificates.

Medically reviewed by Dr. Ashutosh A Shah · Published 23 September 2026 · Last reviewed 23 September 2026

Pilonidal sinus symptoms are pain on sitting, a tender lump near the tailbone, and discharge of pus or blood that settles and comes back. The sinus itself is a small tunnel in the skin at the top of the buttock cleft. It is commonly mistaken for a recurring boil.

Most people arrive at this question the same way. There was a painful swelling near the tailbone. It burst, or was drained, and it got better. Everyone called it a boil. Then it came back, in the same place, and now there is a small opening that leaks something onto your underwear every few weeks.

Boils do not do that. A boil is a one-off infection of a single hair follicle, and once it has drained, that is usually the end of it. Something that returns to the exact same spot again and again is not a run of bad luck, it is a structure that is still there in between. This page explains what that structure is, how to tell it from the things it gets confused with, and what to do next.

What is a pilonidal sinus, and where exactly is it?

A pilonidal sinus is a small tunnel, or tract, that runs from the skin surface into the fatty tissue at the top of the cleft between the buttocks. It contains trapped hair and debris, which the body treats as a foreign object, so it becomes inflamed and infected repeatedly.

The name is literally a description. It comes from the Latin pilus, meaning hair, and nidus, meaning nest. A nest of hair, under the skin.

The location is specific and worth being precise about, because it is how the condition is separated from several others:

• At the top of the natal cleft, which is the groove between the buttocks, in the midline, usually over or just above the tailbone.
• Several centimetres away from the anus, not next to it. This distance is the single most useful thing for telling it apart from an anal fistula.
• Usually with one or more tiny openings, called pits, sitting exactly in the midline. These are often no bigger than a pinhole and are easy to miss.
• Often with a second, larger opening off to one side, which is usually the one people actually notice, because that is where the discharge comes out.

The two-opening pattern is characteristic. Hair works its way in through the midline pit, the body walls it off into a cavity, and the cavity finds a way to drain, generally sideways. That is why the hole you can see and the hole that caused the problem are often not the same hole.

What are pilonidal sinus symptoms, and how do they differ from a boil?

The distinguishing feature is not any single symptom, it is the pattern. A boil appears once, drains and resolves. Pilonidal sinus symptoms recur in the same midline spot over months or years, with quiet periods in between, and there is usually a small permanent opening left behind after each flare.

The symptoms themselves, in the order most people notice them:

• Pain on sitting, especially on a hard chair, in a car or on a two-wheeler. Often the first complaint, and often dismissed as a bruise from sitting too long.
• A tender lump or swelling at the top of the buttock cleft, which may feel firm or fluid-filled.
• Discharge, pus, blood or a clear fluid, onto underwear. It may have a smell.
• A small opening or dimple in the skin that does not go away between flares.
• Redness and heat over the area during a flare.
• Itching or a pricking sensation, sometimes with a visible hair emerging from an opening.
• Pain on standing up after sitting for a while, or on bending.

Now the comparison, because at least four other things present in roughly this area:

Two rows in that table deserve a sentence of their own. If you also get painful lumps in your armpits or groin, mention it, because that points toward hidradenitis suppurativa, which is a chronic skin condition managed quite differently and not a one-off surgical problem. And if the opening is close to your back passage rather than up at the tailbone, or you have diarrhoea, blood in your stool, abdominal pain or unexplained weight loss, say that too, because an anal fistula linked to inflammatory bowel disease is a completely different diagnosis with a completely different treatment. Both of these sit in the published differential diagnosis for pilonidal disease set out in the StatPearls clinical review of pilonidal cyst and sinus, and both are missed regularly. The NHS page on hidradenitis suppurativa describes what that condition looks like if the description above sounds familiar.

Why does it keep coming back when a boil does not?

Because a boil is an event and a pilonidal sinus is a structure. Once the infection in a boil clears, there is nothing left. With a pilonidal sinus, the tunnel and its hair-filled cavity are still sitting there after the flare settles, so the next hair that works its way in starts the whole process again.

The cycle, which is what makes the pattern recognisable:

1. Loose hair collects in the cleft. It comes from the back and scalp, and gathers in the groove.
2. Movement and sitting drive it point-first into the skin, through a midline pit or a stretched follicle.
3. The body treats the hair as a foreign body and walls it off, creating a cavity.
4. The cavity gets infected, swells and becomes painful. This is the flare you notice.
5. It drains, either on its own or with medical help, and the pain settles. You feel better and assume it is over.
6. The tunnel remains. Nothing has removed it. The cycle restarts.

This is why "it got better on its own last time" is not reassurance. Getting better is part of the pattern, not the end of it. In our practice in Surat, the most common history we hear is three or four episodes over two or three years, each one treated as a separate boil, before anybody used the word pilonidal.

Who gets pilonidal sinus?

It is most common in young adults, and roughly twice as common in men as in women. Published figures put the incidence at around 26 per 100,000 people, with men affected about 2.2 times more often than women. Body hair, prolonged sitting and a deep cleft all increase the risk.

The recognised risk factors:

• Being male. The NHS puts this down largely to men tending to be hairier.
• Being a young adult. It typically starts after puberty and is unusual to begin in later life.
• Sitting for long periods. Drivers, desk workers, students and anyone with a long commute. The NHS names prolonged sitting directly.
• Coarse or plentiful body hair, particularly over the lower back and buttocks.
• A deep natal cleft, which traps more hair and holds more moisture.
• Being overweight, which tends to deepen the cleft.
• A family history. It runs in families more often than people expect.
• Friction, sweating and local irritation in the area.

A word about hygiene, since it appears on every risk factor list including the published ones and causes a lot of unnecessary shame. Poor hygiene is a contributing factor, but this condition occurs constantly in scrupulously clean people, and the primary drivers are hair, anatomy and friction rather than washing habits. If you have been told this happened because you are not clean, that is not a fair account of the disease.

What does an infected flare feel like, and what happens in between?

A flare is obvious: increasing pain, a hot tender swelling, and often discharge when it bursts or is drained. The quiet phase is the part that confuses people, because most of the time a pilonidal sinus causes few or no symptoms at all. The NHS puts it plainly, that most people do not notice it unless it becomes infected.

During an acute flare you would typically notice pain that builds over a day or two, a swelling that becomes tense and tender, redness and warmth over it, difficulty sitting or lying on your back, and sometimes a discharge of pus or blood with sudden relief of the pressure. You may feel generally unwell.

In the quiet phase there may be nothing at all, or only a small opening that occasionally leaks a little fluid, mild discomfort on long sitting, a dimple or pit you can see if you look, and an occasional twinge. Many people go months between episodes.

That alternation is the trap. Each recovery feels like a cure, so nothing gets done, and the next flare arrives as a surprise. If you can look back and count two or more episodes in the same spot, the quiet phase you are currently in is not a resolution. It is an interval.

How is pilonidal sinus diagnosed?

It is a clinical diagnosis, made by a doctor looking at the area. In a straightforward case, no blood tests, scans or other investigations are needed. The finding that confirms it is one or more midline pits at the top of the buttock cleft, usually with a track running upward or off to one side.

What the examination actually involves, since the anticipation is worse than the event:

• You lie on your front, or on your side with your knees drawn up. It takes a minute or two.
• The doctor looks for midline pits, the pinhole openings that make the diagnosis. Good lighting matters more than anything else here.
• The surrounding skin is examined for secondary openings, scarring from previous episodes, redness and any current collection of pus.
• The area near the anus is checked to make sure this is not an anal fistula. This is a look, and it is the reason the examination extends further than you might expect.
• Other areas may be asked about or examined, such as the armpits and groin, if hidradenitis suppurativa is a possibility.

Imaging such as an ultrasound or MRI is reserved for cases where the diagnosis is unclear or the tract system appears complicated, usually after previous surgery. If you are offered a scan straight away for a simple, typical presentation, it is entirely reasonable to ask what question it is meant to answer.

One more thing to raise without being asked: if there has been an opening or wound in this area that has never fully healed over a period of years, say so specifically. Long-standing non-healing wounds occasionally need a different kind of assessment, and it is a question worth answering early rather than assuming.

What should you not do at home?

Do not squeeze it, do not try to drain it yourself, and do not shave the area unless a doctor has specifically advised it. Squeezing pushes infection deeper into the tissue rather than out of it, and shaving creates short, sharp-tipped hairs that penetrate skin more easily than untouched hair does.

The list of things that make this worse:

• Squeezing or pressing a swelling to make it burst. The tissue here is loose and the infection spreads sideways and deeper. This is the single most common self-inflicted worsening we see.
• Opening it with a needle or blade. An abscess needs draining properly, under proper conditions, by someone who can see what they are doing.
• Shaving or waxing the area on your own initiative. The NHS advice is explicit: keep the area clean, and do not shave it unless a doctor advises you to.
• Applying strong antiseptics, spirit or home remedies into an open sinus. They damage healing tissue and do not clear a tract.
• Taking leftover antibiotics from a previous course. Antibiotics do not drain an abscess, and a partial course selects for resistance. If antibiotics are appropriate, a doctor decides that.
• Hot packs applied for days while it gets worse. Warmth may ease discomfort, but a swelling that is growing and increasingly painful needs to be seen, not waited out.
• Ignoring it because the last one settled. Covered above. Settling is part of the pattern.

What is reasonable in the meantime: wash the area gently with plain water or a mild cleanser, dry it thoroughly, wear loose breathable clothing, use a cushion for sitting, and take simple pain relief you already take safely.

When is a pilonidal infection an emergency?

Seek medical care the same day if the pain is severe and increasing, if redness is spreading outward from the area, if you have fever or chills, or if you feel generally unwell. These suggest an abscess that needs draining or an infection spreading beyond the local area, and neither improves with waiting.

Get seen urgently if you have any of the following:

• Severe pain that is getting worse by the hour rather than the day
• Redness spreading out from the swelling, particularly if you can see it advancing
• Fever, chills, shivering or feeling generally unwell
• A swelling that is tense, hot and rapidly enlarging
• Bleeding that does not stop with gentle pressure
• Heavy discharge with a strong smell
• Diabetes, a weakened immune system, or immunosuppressant medication, in which case any infection in this area should be reviewed early rather than watched

The NHS advises an urgent appointment for a small lump at the top of your bottom that is painful, bleeding or leaking pus. Fuller guidance is on the NHS page on pilonidal sinus. An abscess is drained, and that is usually a quick procedure bringing rapid relief. It is not the definitive treatment of the sinus, but it is the right first step when the area is acutely infected.

What does treatment involve once it is diagnosed?

Broadly, an acute abscess is drained first to settle the infection, and the sinus tract itself is dealt with separately once things have calmed down. There is more than one way to treat the tract, they differ considerably in recovery time and in how likely the problem is to return, and the right choice depends on how extensive your disease is and whether you have been operated on before. That decision belongs in a consultation with someone who can examine you, and the options are set out in full in our article on pilonidal sinus that keeps coming back and how it is treated. This page is about working out whether that is what you have.

What can you do right now, before you are seen?

Three things: write down the history, look at the area properly once, and get an appointment rather than waiting for the next flare. The history is genuinely useful to whoever examines you, and almost nobody arrives with it.

What to prepare:

1. Count the episodes. How many times, roughly when, and whether each one was in the same spot. Two or more in the same place is the pattern that matters.
2. Note what was done each time. Whether anything was drained, whether antibiotics were given, whether it burst on its own.
3. Note whether an opening has ever fully closed between episodes, or whether something has been leaking continuously.
4. Check whether you get similar lumps anywhere else, especially the armpits, groin or under the breasts. Mention it either way.
5. Note any bowel symptoms such as diarrhoea, blood in the stool, abdominal pain or weight loss, and any family history of bowel disease.
6. Look at the area once, carefully, with a mirror or with help, in good light. You are looking for tiny midline pits and for any second opening off to the side. Look, do not probe, and do not squeeze.
7. Book the appointment during a quiet phase if you can. The tract is easier to assess properly when the area is not acutely inflamed, and planning is easier than emergency drainage at eleven at night.

In the meantime, keep the area clean and dry, keep sitting time broken up, and do not start shaving it.

How is pilonidal sinus assessed at Elegance Clinic, Surat?

Dr. Ashutosh A Shah holds an M.Ch. in Plastic Surgery with over 22 years of reconstructive practice in Surat, Gujarat. His full qualifications are published on the certificates page.

Assessment here starts with confirming the diagnosis rather than assuming it, which means specifically checking for midline pits, examining near the anus to exclude a fistula, and asking about lumps elsewhere on the body. A meaningful number of people referred with "recurrent pilonidal sinus" turn out to have something else, and finding that out before an operation rather than after is the entire point of the examination.

Patients are also told plainly where they are in the disease: a first isolated episode, an established sinus, or a complex recurrent problem, because those three situations lead to quite different conversations. Reconstructive procedures are described on our reconstructive surgery page, and if you are here after a hand or finger injury instead, see our guide to finger injury recovery.
 

Next step

If you can count two or more painful episodes in the same spot near your tailbone, or you can see a small opening that has never fully closed, that is enough to have it looked at, and the best time is now rather than during the next flare. Book an appointment with Dr. Ashutosh Shah in Surat, call +91 83205 00350, or contact the Elegance Clinic team.

Medical disclaimer: This article is for education only and is not a substitute for professional diagnosis or treatment. Several different conditions cause pain and discharge in this area and they are managed very differently, so a diagnosis needs an examination. A painful, rapidly swelling area with fever may be an abscess and needs urgent medical attention. Please consult Dr. Ashutosh A Shah or a qualified surgeon.

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About the Author

Dr. Ashutosh Shah, MBBS, MS, MCh (Plastic Surgery), DNB, is the Director of Elegance Clinic, Surat, with over 22 years of experience across cosmetic and reconstructive surgery.