The most common cause of a lump in the crease between your buttocks is a pilonidal cyst, a pocket that forms under the skin near the tailbone and fills with hair and skin debris. Other possibilities include a perianal abscess, a thrombosed hemorrhoid, or a benign growth like a lipoma or sebaceous cyst. The location, pain level, and other symptoms can help narrow down what you’re dealing with.
Pilonidal Cyst: The Most Likely Cause
A pilonidal cyst sits right at the top of the buttocks crease, near the tailbone. It starts as a small pocket in the skin, and loose hairs work their way into it over time. Many people have one without knowing it. The cyst only becomes obvious when it gets infected, which can happen suddenly.
Signs of an infected pilonidal cyst include a painful, swollen area near the tailbone, a visible pit or dimple at the top of the crease, and sometimes pus or blood leaking from the skin. Draining pus often has a noticeable odor. Before infection sets in, you might just feel a firm, tender bump that seems to appear out of nowhere.
Pilonidal disease is far more common in younger adults. The highest rates occur in men around age 20 and women around age 18. Overall, about 72% of cases occur in males. People with thick or coarse body hair, those who sit for long periods, and those with deeper buttocks creases are more prone to developing them. Rates of pilonidal disease have been rising steadily: a large Danish study found the incidence climbed from about 26 per 100,000 people in the late 1990s to nearly 40 per 100,000 by 2021.
Perianal Abscess
If the lump is closer to your anus rather than up near the tailbone, it could be a perianal abscess. This is a collection of pus caused by an infected gland just inside the anal canal. It typically feels like a hard, painful lump near the opening, and the skin around it may look red and swollen. You might also notice fever, night sweats, fatigue, or pain during bowel movements.
A perianal abscess needs prompt medical attention. Left untreated, it can develop into a fistula, which is an abnormal tunnel between the inside of the anal canal and the outer skin. Somewhere between 30% and 70% of people with an anorectal abscess already have or will develop a fistula. Fistulas cause recurring cycles of swelling, pain, and spontaneous drainage of pus or blood, and they generally require a procedure to resolve.
Thrombosed Hemorrhoid
A thrombosed hemorrhoid is a blood clot that forms inside an external hemorrhoid, right at the edge of the anus. It shows up as a dark blue or purple lump that you can see or feel. The pain can be intense, especially in the first 48 to 72 hours. Unlike a pilonidal cyst, which sits higher in the crease near the tailbone, a thrombosed hemorrhoid is directly at the anal opening. If you notice a blue-tinted, extremely tender bump in that spot, this is the likely culprit.
Lipomas and Sebaceous Cysts
Not every lump between the buttocks is infected or urgent. Two common benign growths can show up in this area.
A lipoma is a collection of fat cells just under the skin. It feels soft and doughy, moves easily when you press on it, and is typically painless. A sebaceous cyst, on the other hand, is firmer, may feel tender to the touch, and sits within the skin itself rather than beneath it. Neither of these is dangerous, but a sebaceous cyst can become infected over time, at which point it starts to resemble an abscess with redness, warmth, and pain.
The key difference is mobility and texture. If the lump is soft, movable, and painless, it’s more likely a lipoma. If it’s firm and slightly tender, a cyst is more probable.
Sacral Dimple vs. a New Lump
Some people notice a small indentation near the base of their spine and wonder if it’s related to a lump. A sacral dimple is a congenital feature, meaning you’re born with it. A typical sacral dimple sits low on the back near the buttocks crease, has a visible bottom, and has no other skin changes around it. This is harmless and unrelated to pilonidal disease.
An atypical sacral dimple, located higher on the back or accompanied by a tuft of hair, skin discoloration, or a lump, is different and worth having evaluated with imaging. But if you’ve had a dimple in that area your whole life with no changes, it’s not the same thing as a new, painful bump.
Treatment for Pilonidal Cysts
If a pilonidal cyst is infected and forming an abscess, the first step is usually incision and drainage. This can be done as an outpatient procedure, and most people return to work immediately. About 58% of patients heal within ten weeks after a simple drainage, though there is a meaningful chance of recurrence. Simple drainage alone has a recurrence rate of 40 to 60%, which is why follow-up care matters.
For cysts that keep coming back, surgical options include excision with flap closure, where the wound is closed off the midline to reduce the chance of recurrence. Modified flap procedures bring recurrence rates down to as low as 0 to 6%, compared to roughly 15 to 17% for midline closures.
Non-surgical approaches also exist. Injection of a chemical sclerosing agent has shown success rates between 67% and 95% in different studies, with the advantage of no time off work, faster healing (around 16 days on average), and less pain compared to excision. For mild or early-stage disease without an abscess, regular hair removal from the area, either by shaving or laser depilation, can be enough to manage the condition.
Preventing Recurrence
Pilonidal cysts have a frustrating tendency to come back. The most effective prevention strategy targets the root cause: loose hair getting trapped in the skin. Keeping the gluteal cleft free of hair through regular shaving or laser hair removal significantly reduces recurrence. One military medical center study found that weekly shaving of the area, combined with basic hygiene education, decreased the need for surgery and allowed patients to maintain near-normal activity levels.
Laser hair removal offers a more permanent solution and is now recommended as a routine part of post-treatment care. Beyond hair removal, keeping the area clean and dry, avoiding prolonged sitting when possible, and wearing loose-fitting clothing can all help reduce pressure and friction in the crease.
Red Flags That Need Prompt Attention
Some symptoms suggest the lump has progressed beyond something you can wait out. Fever, night sweats, spreading redness around the lump, worsening pain, or pus draining from the area all point to an active infection that needs medical treatment. Pain during bowel movements, pain in the lower abdomen, or a lump that’s growing rapidly are also reasons to be seen quickly. An anorectal abscess in particular can worsen fast and lead to complications if drainage is delayed.