A small hole or pit in the skin above your anus, typically in the crease between your buttocks, is most likely a pilonidal sinus. This is a common inflammatory condition where a tiny opening forms in the skin of the natal cleft, the groove that runs from the base of your tailbone down to your anus. It can sit there quietly for months or years, or it can become infected and painful. Less commonly, what you’re seeing could be a sacral dimple you were born with or, rarely, a fistula tract connected to the anal canal.
What a Pilonidal Sinus Actually Is
A pilonidal sinus is a small tunnel or pit that develops in the skin at the top of your buttock crease, near the tailbone. The exact cause isn’t fully settled, but the leading explanation is that loose hairs in the gluteal cleft get pushed into the skin, either by friction, pressure, or a slight vacuum effect created when the skin lifts off the tissue underneath during movement. Once hair or skin debris gets trapped beneath the surface, your body treats it as a foreign object and triggers inflammation. That inflammation creates a small cavity, and more hair can work its way in over time, making the problem worse.
Another theory focuses on the hair follicles themselves. A follicle in the natal cleft becomes clogged with keratin (the protein your skin and hair are made of), swells, and eventually ruptures under the skin. The resulting pocket then collects loose hairs secondarily. Either way, the end result is the same: a pit in the skin that may connect to a deeper tract or cavity underneath.
Pilonidal disease affects men roughly four times more often than women. It most commonly shows up in people between their late teens and early thirties, especially those who sit for long periods, have thick or coarse body hair, or carry extra weight. Occupations that involve prolonged sitting, like truck driving, are well-known risk factors.
When the Pit Stays Quiet
Many people discover the pit by accident, in the shower or while drying off, and it causes no symptoms at all. An asymptomatic midline pit doesn’t necessarily require treatment. German national guidelines, for instance, don’t recommend surgery on pits that aren’t causing problems, since operating on a painless pit doesn’t lower the chance of future issues compared to waiting and treating only if symptoms develop.
If you have a painless, non-draining pit, the main thing you can do is keep the area clean and dry. Removing hair from the natal cleft through shaving or other methods can reduce the chance of hair working its way into the opening. Avoiding prolonged pressure on the area (taking breaks from sitting, for example) also helps.
Signs of Infection
The trouble starts when the sinus becomes infected, which can happen quickly, sometimes over just a few days. The first thing most people notice is pain, particularly when sitting. The severity varies widely. Some people feel mild discomfort; others have pain intense enough to make sitting nearly impossible.
Other signs of an infected pilonidal sinus include:
- Swelling and redness around the pit, sometimes forming a visible lump
- Pus or blood draining from the opening
- A foul smell from the drainage
- Warmth and tenderness in the surrounding skin
If you develop these symptoms, you need medical attention. An infected pilonidal sinus won’t typically resolve on its own. Left untreated, the infection can form an abscess, a painful, pressurized pocket of pus that may need to be drained.
How It’s Treated
For an acute infection or abscess, the first step is usually incision and drainage, a minor procedure where a doctor opens the abscess, drains the pus, and cleans out any hair and debris. This provides quick relief but doesn’t always prevent the problem from coming back.
For recurrent or complex pilonidal disease, surgical options aim to remove the sinus tract entirely. The wound can either be left open to heal from the inside out, or closed with stitches. Leaving the wound open tends to have a lower recurrence rate, though it takes longer to heal. Recovery from pilonidal surgery generally takes about three weeks on average, with published timelines ranging from 13 to 30 days depending on the procedure and the individual.
Even after surgery, pilonidal disease comes back in roughly 7% of cases. Procedures that close the wound along the midline of the crease carry a higher recurrence risk than techniques that shift the closure off to one side, away from the deepest part of the cleft where hair accumulates most easily.
Could It Be Something Else?
A sacral dimple is the main alternative. These are congenital, meaning you’re born with them. They sit in the same general area (lower back, just above the buttock crease) and are usually shallow, small, and completely harmless. If you’ve had this dimple for as long as you can remember and it has never been painful, red, or draining, a sacral dimple is a strong possibility. The key difference: sacral dimples are present from birth, while pilonidal sinuses develop later, typically in adolescence or early adulthood.
A perianal fistula is less likely but worth knowing about. This is an abnormal tunnel that connects the inside of the anal canal to an opening in the skin near the anus. Fistulas tend to sit closer to the anus itself (often within a few centimeters) rather than higher up in the buttock crease. They’re usually accompanied by pain, swelling, and a palpable tract you can feel running toward the anus. If the hole you’re noticing is very close to your anal opening and drains intermittently, a fistula is worth considering, though it’s much less common than a pilonidal sinus.
What to Do Next
If the pit is painless, not draining, and not red or swollen, you can reasonably keep an eye on it while maintaining good hygiene in the area. Keep the cleft clean, dry, and as hair-free as practical. If you notice any pain, swelling, drainage, or odor developing, those are signs of infection that call for a medical visit sooner rather than later. Early treatment of an infected sinus is simpler and heals faster than dealing with a full-blown abscess.