To understand pilonidal sinus disease, it helps to break down its name. Pilo- comes from the Latin word for hair (pilus), and -nidal comes from the word for nest (nidus). So, a “pilonidal sinus” is literally a “nest of hair” under the skin. It is a condition that occurs almost exclusively in the natal cleft (the crease of the buttocks).

The condition begins when one or more hair follicles in the natal cleft become stretched and open. A sinus (a small channel or tract) then forms, leading from the surface of the skin down into the deeper fatty tissue. This tract can become blocked with loose hairs and other skin debris. This debris, combined with the warm, moist, and low-oxygen environment of the deep natal cleft, creates a perfect breeding ground for bacteria.

• A pilonidal cyst refers to the encapsulated cavity under the skin that contains this hair and debris.
• A pilonidal abscess is what happens when this cyst becomes acutely infected with bacteria, filling with pus and causing a painful, swollen lump.
• Pilonidal sinus disease is the chronic condition, characterized by one or more sinus openings and a tendency for recurrent inflammation and abscess formation.

In the clinic, I often see this misdiagnosed as a simple boil. But when symptoms recur in the same spot near the tailbone, especially with visible hair inside, pilonidal sinus disease is usually the culprit.

For many years, it was believed that pilonidal cysts were a congenital condition, something a person was born with. However, the modern understanding is that pilonidal disease is an acquired condition that develops after puberty.

The primary cause is the penetration of loose, stiff hairs into the skin of the natal cleft. The process is thought to occur as follows:

1. Hair Collection: Loose hairs, often from the head, back, or buttocks, fall and collect in the natal cleft.
2. Follicle Entry: The friction and pressure from sitting and movement drills these stiff hairs, tip-first, into the openings of the hair follicles.
3. Foreign Body Reaction: The body treats this embedded hair as a foreign object, creating an inflammatory reaction around it.
4. Sinus Tract Formation: This chronic inflammation leads to the formation of a sinus tract around the hair shaft, leading from the skin surface down into the subcutaneous tissue.
5. Cyst and Abscess: This tract can become blocked, creating a cyst that fills with more hair, skin debris, and bacteria. If this cyst becomes acutely infected, it evolves into a painful abscess.

What surprises many is that this isn’t a birth defect, it develops over time due to friction, hair growth, and pressure. I tell patients it’s more mechanical than genetic in most cases.

A person develops pilonidal disease due to a combination of anatomical features and environmental factors that promote the burrowing of hair into the skin. It is not contagious and is not caused by poor hygiene alone, although keeping the area clean and dry can help in prevention.

The key risk factors for developing pilonidal sinus disease include:

• Age and Gender: It is most common in young men, typically from puberty to age 40. It is rare in children and adults over 40.
• Hair Characteristics: Abundant, coarse, stiff body hair.
• Anatomy: A deep natal cleft, which creates more friction and traps more debris and moisture.
• Lifestyle:
  • Prolonged sitting (e.g., truck drivers, office workers). The condition was famously nicknamed “Jeep Driver’s Disease” during World War II because it was so common among soldiers who spent long hours driving on bumpy roads.
  • Obesity, which can deepen the cleft and increase sweating.
• A Family History: While not directly inherited, a family history can be a risk factor, likely due to inheriting similar traits like hair type and body conformation.

I’ve seen this occur in athletes and office workers alike. It’s less about hygiene and more about friction, sweat, and trapped hair. Preventive care like shaving or laser hair removal can really help in chronic cases.

The signs and symptoms of pilonidal disease vary depending on whether the sinus is inflamed, infected, or draining.

Asymptomatic Pilonidal Sinus

In its mildest form, a person may be completely unaware they have the condition. The only sign might be one or more small, pit-like openings (sinus tracts) in the skin in the midline of the buttock crease.

Acute Pilonidal Abscess

This is often the first time a person seeks medical attention. The presentation is sudden and painful.

• Rapid onset of a painful, swollen, red, tender lump.
• May drain pus or bloody fluid with a foul odor.
• Fever and malaise (feeling unwell).

Chronic Pilonidal Sinus

• Characterized by recurrent episodes of mild to moderate pain or swelling.
• Persistent drainage of fluid or pus from the sinus openings.
• Itching and discomfort.

What I always look for is a dimple or opening near the midline of the lower back. If it’s draining pus and tender, it’s likely a pilonidal sinus and not just a skin infection.

Diagnosis is usually clinical, based on patient history and physical examination.

• Medical History: The doctor will ask about the onset of pain, swelling, or drainage.
• Physical Examination: This is the key to diagnosis. The doctor will examine the skin in the natal cleft.
  • They will look for the characteristic sinus pits in the midline.
  • If an acute abscess is present, it will be a red, swollen, tender mass.
  • In chronic disease, the doctor may be able to probe the sinus tract gently to determine its depth and direction.

Imaging studies like an MRI or CT scan are almost never needed unless the disease is extremely complex or there is a concern for a deeper infection.

If a patient comes in with recurrent drainage or pain near the tailbone, I check for tiny sinus openings, usually that’s all I need to confirm the diagnosis.

Treatment depends on the severity and recurrence of the condition. Options range from conservative management to surgical intervention.

1. Treatment of an Acute Abscess

The urgent and necessary treatment for a painful pilonidal abscess is a procedure called incision and drainage (I&D).

• This is often performed in an emergency department or a doctor’s office under local anesthesia.
• The doctor makes a small incision into the abscess to allow all the pus and debris to be completely drained out. This provides immediate pain relief.
• The wound is then cleaned and often packed with gauze. The packing may need to be removed and replaced over the next few days as the cavity heals from the inside out.
• While I&D effectively treats the acute infection, it is important to understand that it does not cure the underlying pilonidal sinus disease. The recurrence rate after I&D alone is very high.

2. Definitive Surgical Treatment (for chronic or recurrent disease)

For chronic or recurrent pilonidal disease, surgery is the only definitive cure. The goal of surgery is to completely remove all the sinus tracts and the underlying cyst cavity to prevent future infections. There are many different surgical techniques, and the best option depends on the extent of the disease and the surgeon’s preference.

• Excision with Primary Closure: The surgeon cuts out the entire diseased area and stitches the wound closed directly. Higher risk of infection but faster healing if successful.
• Excision with Healing by Secondary Intention: The surgeon cuts out the diseased area but leaves the wound open to heal from the bottom up. This requires extensive wound packing and dressing changes but has a lower risk of infection.
• Flap Procedures (Advanced Reconstruction): For complex or recurrent disease. Describe procedures like the Limberg flap or Karydakis flap. The surgeon removes the diseased tissue and then mobilizes a flap of healthy skin and fat from the side of the buttock to cover the defect and flatten the natal cleft, which significantly reduces the chance of recurrence (American Society of Colon and Rectal Surgeons [ASCRS], 2020).

Prevention of Recurrence

After surgery, preventing recurrence is key. This involves keeping the area clean and dry and, importantly, keeping the area free of hair. Methods like regular shaving or, more permanently, laser hair removal in the natal cleft can dramatically reduce the chance of developing a new pilonidal sinus.

I always stress the importance of aftercare. Even after surgery, daily hygiene and hair control are key to prevent recurrence which is frustratingly common if the area isn’t cared for properly.

Pilonidal disease is a common skin condition caused by hair burrowing into the skin of the buttock cleft, leading to chronic infection and abscesses. It is linked to factors like hair type and prolonged sitting, and it is not a dangerous condition but can be very painful and recurrent. While an acute abscess requires urgent drainage, the definitive treatment for chronic disease is surgery. What I always tell patients is this: pilonidal disease is like a bad habit, it keeps coming back if ignored. But with the right treatment plan and consistent aftercare, you can break the cycle and move on comfortably.

American Society of Colon and Rectal Surgeons (ASCRS). (2020). Pilonidal disease. Retrieved from https://fascrs.org/patients/diseases-and-conditions/a-to-z/pilonidal-disease-expanded-version

Cleveland Clinic. (2022). Pilonidal Disease (Pilonidal Cyst). Retrieved from https://my.clevelandclinic.org/health/diseases/15400-pilonidal-disease

Mayo Clinic. (2024). Pilonidal cyst. Retrieved from https://www.mayoclinic.org/diseases-conditions/pilonidal-cyst/symptoms-causes/syc-20376329