Pilonidal cysts form when hair becomes trapped beneath the skin near the tailbone, triggering an inflammatory reaction in the tissue underneath. They develop in the natal cleft (the crease between the buttocks), typically starting as a blocked or irritated hair follicle that ruptures below the skin’s surface. The condition overwhelmingly affects young people, with an average onset around age 15 in females and 17 in males, and it’s roughly twice as common in males as females.
How a Pilonidal Cyst Actually Forms
The process starts with the hair follicles in the natal cleft. After puberty, hormonal changes cause these follicles to produce more keratin, a protein that can clog and distend the follicle. When a follicle becomes blocked, a localized infection develops, causing swelling that further traps the follicle. Eventually, the infected follicle ruptures into the deeper tissue beneath the skin, forming a pocket (the cyst) that fills with hair, debris, and pus.
Once this pocket exists, loose hairs can continue to work their way into it. The motion of walking, sitting, and general friction in the area acts like a drill, pushing shed hairs downward through the skin. The cyst can then develop into a sinus, which is a tunnel-like tract that may open to the skin’s surface through one or more small pits along the midline of the cleft. These openings sit about 4 to 5 cm from the anus, which is one way doctors distinguish pilonidal disease from other conditions like perianal abscesses.
Risk Factors That Make It More Likely
Not everyone who has hair in their natal cleft develops a pilonidal cyst. Several factors raise the risk significantly:
- Thick or coarse body hair. More hair means more raw material to become trapped. Conditions that increase body hair growth, such as polycystic ovary syndrome (PCOS), have been linked to higher rates of pilonidal disease in at least two studies.
- Obesity. Excess weight deepens the natal cleft, increases moisture and sweating, and adds pressure to the area when sitting.
- A deep natal cleft. A naturally deeper crease creates a warmer, more enclosed environment where hair and sweat accumulate.
- Sedentary lifestyle or prolonged sitting. Extended time in a chair increases pressure and friction against the tailbone. The condition was so common among World War II soldiers who spent long hours in bumpy Jeep seats that it earned the nickname “Jeep seat disease.” More than 80,000 U.S. soldiers were hospitalized for it during the war.
- Family history. Genetics play a role, likely through inherited traits like hair type, cleft depth, and skin characteristics.
Poor hygiene in the area can also contribute, since sweat and bacteria compound the irritation. The bacteria most commonly found in pilonidal abscesses are a mix of anaerobic species (the kind that thrive in low-oxygen environments like deep skin folds), which were present in 77% of cases in one study. Other research points to staph bacteria as the most common single culprit.
What It Feels Like
A pilonidal cyst that isn’t infected may cause no symptoms at all, or just mild tenderness near the tailbone. You might notice a small dimple or pit in the skin at the top of your buttock crease without thinking much of it.
When infection sets in, the area becomes painful, swollen, red, and warm to the touch. Sitting can become genuinely difficult. The cyst may drain on its own, producing pus or blood-tinged fluid that often has a foul smell. Some people develop a low-grade fever. The pain tends to build over several days before either resolving or worsening enough to need medical attention.
Pilonidal disease often becomes a recurring problem. After an initial episode, the sinus tracts remain in the tissue, creating a pathway for future infections. This cycle of flare-ups and temporary improvement is one of the most frustrating aspects of the condition.
How It Differs From Other Conditions
The location of a pilonidal cyst is its most distinguishing feature. It sits along the midline of the natal cleft, near the tailbone, several centimeters away from the anus. Perianal abscesses, by contrast, form right at the edge of the anus and originate from infected glands inside the anal canal. If swelling or drainage is closer to the anus than the tailbone, it’s more likely a different condition entirely.
Reducing Your Risk
Since trapped hair is the central problem, keeping the natal cleft area free of loose hair is the most effective prevention strategy. Shaving works but is hard to do consistently in such an awkward spot, and razor irritation can sometimes make things worse. Waxing and depilatory creams offer temporary results but tend to have poor long-term compliance.
Laser hair removal has the strongest evidence behind it. Studies in adults show it can reduce pilonidal recurrence rates by 10 to 40%. One study found a dose-response relationship: patients who achieved 50% hair reduction saw recurrence drop by 78%, and those who reached 75% hair reduction had no recurrences at all. The more hair you remove, the better the protection.
Beyond hair removal, practical steps that reduce friction and moisture help. Avoid sitting for long uninterrupted stretches. If your job requires extended sitting, take regular breaks to stand and walk. Keep the area clean and dry. Maintaining a healthy weight reduces pressure on the natal cleft and decreases the depth of the crease where hair collects.
Treatment Options
An actively infected pilonidal cyst usually needs to be drained. This is a relatively quick procedure where the abscess is opened and the pus is released, providing near-immediate pain relief. The cavity is then packed with gauze and allowed to heal from the inside out over several weeks.
For recurring pilonidal disease, surgery to remove the entire sinus tract is the more definitive option. Several techniques exist, ranging from simple excision (cutting out the affected tissue and leaving the wound open to heal gradually) to flap procedures that close the wound with nearby skin. Recovery times vary from a few weeks to a couple of months depending on the approach. Open wounds heal more slowly but tend to have lower recurrence rates than wounds that are stitched closed immediately.
After any surgical treatment, hair removal around the area is strongly recommended to prevent new hairs from re-entering the healing wound and restarting the cycle.