A Buttock Cyst That Keeps Growing: Why It Flares Up and When to Remove It

"Doctor, it was the size of a bean. I left it alone for two years, then last month it swelled up, and now it hurts to sit down."

I hear that sentence often, and the people saying it are almost always pointing at the same place: the buttock.

A cyst on the buttock (an epidermal cyst, also called an epidermoid cyst, a closed sac lined with skin cells and filled with keratin) is pathologically the same thing as one behind your ear or on your back. What differs is where it lives. You sit for hours a day, the gluteal muscles move with every step, and from the day you first noticed it, that sac has been getting compressed and rubbed.

So of all the cysts a person has, the one on the buttock is usually the first to cause trouble.

Why a buttock cyst tends to get worse the longer you wait

Think of a cyst as a sealed pouch under the skin. Its lining keeps producing keratin, so it slowly enlarges and does not resolve on its own. That is true of every cyst, wherever it sits.

What the buttock adds is pressure, and it works in three directions.

When you sit, your body weight bears down on that spot, so the wall of the sac takes sustained shear. Daily movement and clothing rub the small surface opening (the punctum, the tiny pore you can often see on top of a cyst) and keep it irritated. On top of that, this area traps heat and moisture, so bacteria have an easier time settling in.

Put those three together and the usual result is that the cyst gets inflamed sooner. Growth speed barely differs. And once it has been inflamed even once, the sac wall starts sticking to the tissue around it, which makes each later flare easier to trigger and slower to settle.

Most of the people I see in clinic didn't come because it got bigger. They came on the third flare, when sitting had become unbearable, having toughed out the first two.

Key point: The risk with a buttock cyst isn't its size. It's that the location makes it flare repeatedly, and repeated flares make the eventual surgery harder.

First, is it a cyst or a pilonidal sinus?

Most articles skip this step, but it decides the whole treatment plan.

A painful lump around the buttock or tailbone can be an epidermal cyst, or it can be a pilonidal sinus (a tract that forms when hair works its way under the skin near the tailbone). Both go red, both swell, both can discharge. They are not the same disease.

Getting this wrong has real consequences. Treat a pilonidal sinus like a cyst, clear only the surface portion, and the tract underneath is still there, so it comes back. That is why I don't like to settle the question with eyes and fingers alone.

Ultrasound helps here. It shows whether you are dealing with a bounded, round sac or a tract heading deeper, and how close it sits to the fascia below. I wrote more about the role of imaging in reading subcutaneous lumps in ultrasound diagnosis of subcutaneous tumors.

When should it come out? I don't go by size

Plenty of articles give you a number in centimetres and tell you that anything larger needs surgery. That is not how I look at it.

A cyst sitting quietly, not painful, not often pressed on, is reasonable to monitor. What I do want to treat is any of the following.

It has been inflamed at least once. That tells me the sac wall and the surrounding tissue have already changed, and the next flare will come more easily.

It sits exactly where your weight lands when you sit down. Size doesn't matter much here, because the daily load isn't going to ease off by itself.

It has visibly grown over weeks to months, or it has gone from movable to tethered to the tissue underneath.

Your work or your sport leaves you no room for a flare. If you run, lift, drive long hours or sit all day, one episode costs you several days, and it tends to happen at the worst possible time.

It has started changing how you sit or what you can wear. Once your posture and your clothes have to accommodate it, that is a quality-of-life problem.

Key point: What sets the timing is its history of inflammation and how often it gets compressed, not the number on a ruler.

There is a more important consequence of waiting. Leaving it late changes the whole approach, not just the size of the operation. A cyst that has never been inflamed has a clean plane around the sac and can be lifted out whole. One that has flared several times and scarred in needs more dissection and a longer incision. I go into that in more depth in why cysts come back.

It's flaring right now. Drain it, or remove it?

This is the classic buttock-cyst emergency: swollen like a small ball, red, hot, impossible to sit on.

A cyst in acute inflammation, with pus, is usually not the right moment for a complete excision. The tissue is swollen and the planes are blurred, so hunting for the sac in that state tends to fragment the wall and leave remnants behind, which raises the chance of recurrence rather than lowering it.

The sensible sequence is to bring the pressure and infection down first: usually 2 to 4 weeks of oral antibiotics, with drainage if needed, and once the inflammation has shrunk to a mild level at follow-up, the complete removal of the sac can be scheduled. It does not have to settle completely. A cyst that is only mildly inflamed can usually be removed directly.

So if yours is swollen as you read this, the thing to do is get the inflammation treated, not search for somewhere that will operate tonight. I've covered home care during a flare, and why squeezing is a bad idea, in what to do when a cyst gets inflamed. If you have already squeezed it, or it has burst on its own, read next steps for a cyst you've already squeezed.

A buttock cyst that has been squeezed is harder to operate on

I'll be honest: cysts in this location have an unusually high rate of having been dealt with at home. You can't see it, you can feel it, and it happens to be swollen, so people try.

What comes out when you squeeze is the keratin inside the pouch. The pouch itself stays. And the act of squeezing ruptures the wall, spilling contents into the surrounding tissue, which the body walls off as a foreign body. A clearly bounded sphere turns into a mass of scarred tissue stuck to everything around it.

That is still treatable. It just means I spend longer finding the edges, and the incision can't be as small as it would have been. Which is why I keep telling patients the same thing: resist it, don't squeeze.

If you sit all day or train hard, plan the recovery first

The hard part of buttock surgery comes afterwards: you have to go on living in a seated position.

This area takes two kinds of load at once: compression when you sit, traction when you walk. So recovery planning for the buttock looks nothing like it does for an arm, and you can't just copy one across. I've laid out the timelines by body region, in a table, in how soon you can exercise after cyst surgery.

In practice, before we book anything, think through a few things: whether you have a long flight or a full day of driving coming up, whether there's an important competition or exam, and whether your job lets you stand up and walk around now and then. Scheduling surgery in a gap between those commitments beats taking the next available slot.

How we approach it: see it clearly, then keep the incision small

Our approach to subcutaneous tumours comes down to two sentences.

The first is to see it clearly before anything else. Ultrasound guidance tells me how deep the sac sits, what shape it is, whether it has more than one chamber, and how far it is from the structures underneath. Fat is thick over the buttock, and judging depth by palpation alone is often well off, so being able to see it is what lets me put the incision exactly where it needs to be.

The second is to keep the incision as small as possible. Our aim is to hold the incision within 20% of the diameter of the lesion, rather than laying the lump open along its long axis. Going in through a small opening and lifting the entire sac out with its wall intact is what keeps recurrence low, and it also means the healed mark tends not to stand out (results still vary with your skin, the site, and whether it had been inflamed before).

For anaesthesia we use tumescent local anaesthesia together with gentle pain-relief anaesthesia, not general anaesthesia. You can talk to me throughout, and discomfort is kept well down, so being worried about pain shouldn't be the reason you keep putting this off (sensation still varies between people).

Some suitable cases can be handled with laser treatment for cysts, but a site like the buttock, repeatedly compressed and often previously inflamed, needs an in-person assessment of the sac before we can say whether that fits. The full explanation of complete sac excision is on our cyst treatment page, and other subcutaneous tumours are covered under skin tumour treatment.

Common questions

What happens if I leave a buttock cyst alone?

It won't disappear. The usual course is slow enlargement, followed by a flare at some point when you are run down or the area has had more friction than usual. The more flares it has had, the more tightly the sac adheres to the tissue around it, and the more work a complete removal becomes.

How large does a buttock cyst have to be before it needs surgery?

There is no single measurement that applies to everyone. What I look at is whether it has been inflamed, whether it sits where your weight lands when you sit, and whether it has grown noticeably of late. A small one that gets pressed every day has a better case for removal than a large one that never bothers you.

How do I tell a cyst from a pilonidal sinus near the tailbone?

Location and appearance are the first clues. Cysts are usually off to one side with a single central punctum; a pilonidal sinus sits near the midline of the natal cleft, often with small pits and visible hair. The two do overlap in appearance, so an in-person assessment with ultrasound is more reliable, because the treatment paths differ.

Can it be excised while it's swollen and painful?

During acute inflammation the tissue is swollen and the planes are unclear, and a complete excision attempted then tends to leave sac wall behind. When it is badly swollen, oral antibiotics come first for 2 to 4 weeks, and the excision can be scheduled once it has shrunk to a mild level, without waiting for it to settle completely. A mildly inflamed cyst can usually be removed directly.

Will I have to lie down and avoid sitting for days afterwards?

You don't have to avoid sitting altogether, but for the first few days you should avoid holding one position for long stretches and keep your weight off the wound. The exact timeline depends on the size of the incision and whether it had been inflamed before, and I'll go through it with you at your consultation.

Will the mark on my buttock be obvious?

Incision size is the biggest variable, which is why we hold it within 20% of the lesion diameter. For most people the healed mark is not conspicuous, though skin tension over the buttock and your own healing tendencies both affect the result. A cyst that has been inflamed needs a wider dissection, so the mark is usually more noticeable than with one that never flared.

Next step

If the lump on your buttock has already flared a second time, or if you press on it every time you sit down, it isn't going to improve by waiting another three months.

Bring it in and let me look at it. We'll scan it, and I'll tell you whether it's a cyst or something else, whether now is the right time to treat it, and how small an incision can get the whole sac out. You can arrange a consultation here.

Further reading

• What to do when a cyst gets inflamed
• Why cysts come back
• How soon you can exercise after cyst surgery
• Next steps for a cyst you've already squeezed
• Ultrasound diagnosis of subcutaneous tumors