The Old Theory: Hair Tunneling
For many years, doctors thought pilonidal disease occurred when loose hairs drilled into the skin, like splinters. This idea seemed logical because something similar can happen with a barber’s hair sinus. Still, it never explained why the disease nearly always appears in the same place — the upper buttock crease (natal cleft) — or why 50% of Pilonidal cases lack hair. So, something else was going on.
Dr. John Bascom’s Discovery: The Pit Theory
In the 1980s, surgeon Dr. John Bascom examined hundreds of pilonidal tissue samples under the microscope. He noticed something others had missed:
- Tiny openings in the skin, which he called pits
- Hair and skin debris collected inside these pits, setting off inflammation
- The body reacted just as it does to a splinter — with swelling, infection, and sometimes abscess formation
This proved that pilonidal disease is not congenital and not caused by hair tunneling inward. Instead, it’s acquired, starting with small pits that serve as entry points for debris.
Why This Matters for Patients
- You weren’t born with this — pilonidal disease develops over time.
- It’s not your fault: the shape of your cleft, hair type, and sitting pressure all contribute.
- Treatments focus on removing pits and, in many cases, flattening the cleft so new pits can’t form.
The Role of Blocked Pores: The Follicular Occlusion Tetrad
Pilonidal disease is part of a group of skin conditions called the follicular occlusion tetrad, which includes:
- Pilonidal disease
- Hidradenitis suppurativa
- Dissecting cellulitis of the scalp
- Acne conglobata
All four conditions start when pores or hair follicles get blocked. Once blocked, they can rupture, trigger inflammation, and allow infection. In pilonidal disease, this explains why pits form in the midline cleft and why blocked pores, pressure, and trapped hair are the perfect recipe for flare-ups.
Why This Matters for Medical Professionals
- Bascom’s pit theory replaced the discredited “hair penetration” model.
- Disease origin is follicular occlusion in the midline, not foreign-body penetration.
- Modern procedures — pit picking, Bascom cleft lift, Karydakis, off-midline flaps — all aim to remove or bypass midline pits and flatten the cleft.
- Histology shows epithelial invagination with secondary hair entrapment, consistent with occlusion disease models.
- This aligns pilonidal disease with other occlusion disorders, reinforcing that it is a disease of skin physiology + anatomy, not hygiene.
Clinical takeaway: Eradicate midline pits, avoid midline closures, and flatten the cleft whenever possible.
Everyday Questions
Did this happen because I wasn’t clean enough?
No. Hygiene can help reduce flare-ups, but the root cause is blocked pores and pits, not cleanliness.
If hair is a problem, can shaving cure it?
Shaving may lower risk, but it doesn’t remove existing pits. Also, hair isn’t always the problem; 50% of abscesses lack hair. Medical treatment is usually needed to remove the pits.
Why does it sometimes come back after surgery?
If pits aren’t fully removed, or if the incision is made down the midline (where pits reform easily), recurrence is common. Off-midline approaches are safer.
If this is a skin problem, why is it a Colon & Rectal specialty?
Your skin is your body’s largest organ and acts as a protective barrier against bacteria and parasites. Pilonidal disease is mainly a skin problem because the abscess forms when bacteria breach the protective layer in the cleft between your buttocks. However, due to proximity to the anus, it falls under the Colon & Rectal spectrum.
Does Pilonidal run in families?
Pilonidal disease often runs in families, likely because people inherit the shape and depth of their buttock cleft and a tendency for skin problems caused by blocked pores.
Can I get a Pilonidal from a tailbone injury?
Some people develop pilonidal disease after a tailbone injury, which raises questions. Our Medical Advisers speculate that a pimple or pit may already exist in the buttock’s midline before the injury. The body’s immune system usually handles minor ruptured follicles, but trauma disrupts its defenses, causes swelling, and breaks down tissue walls that keep pimples or pits isolated. As a result, bacteria invade the area and form an abscess.
How the Pores Got Stretched
When standing up, gravity pulls the tissues in the buttock midline downward while the body moves upward. This force, along with slouching when sitting, stretches the pores in the buttock midline. Although our “sit bones” are designed for proper sitting, many people tend to slouch forward in their chairs, which widens these pores more than they should be. They might look like this:
How They Got Full of Gunk
Once the follicles stretch out, they easily collect debris like dead skin cells, sweat, lint, and hair. This buildup blocks the pores, preventing natural oils (sebum) from flowing. The trapped oil causes the follicle to stretch further. As debris accumulates, the follicle becomes inflamed and eventually ruptures, spilling its contents and triggering an inflammatory response. Here in the Pilonidal world, we now call this a “pit”. Pits are bad.
How They Got Infected
The pit marks the start of a Pilonidal abscess. Once the skin’s natural barrier breaks, anaerobic bacteria—those that thrive without oxygen—can invade the fatty tissues of your buttocks and go off exploring. These bacteria multiply rapidly, causing a secondary infection. They invite friends, throw wild parties, and reproduce with abandon. Infections caused by anaerobic bacteria are characterized by abscess formation, foul-smelling pus, and tissue destruction. For those of you reading this right now with an ache at the top of your buttock cleft, this should be starting to sound very familiar…
Key Takeaway
Pilonidal disease starts with blocked pores and pits in the midline cleft — not hairs tunneling inward. Dr. Bascom’s discovery transformed our understanding, aligning pilonidal with the follicular occlusion tetrad of skin disorders. This shift in knowledge explains why modern pit-based and cleft-flattening surgeries work best.
For Medical Professionals: Further Reading
- Bascom J. Pilonidal disease: origin from follicles of hairs and results of follicle removal as treatment. Surgery. 1980;87(5):567–572.
- Bascom J. Pilonidal disease: long-term results of follicle removal. Dis Colon Rectum. 1983;26(12):800–807.
- Vasanth, Vani & Chandrashekar, Byalakere. (2014). Follicular occlusion tetrad. Indian Dermatology Online Journal. 5. 491-3. 10.4103/2229-5178.142517.
Go Here Next:
Now that you know what a Pilonidal is, you’re probably wondering if that’s what is causing your tailbone pain. Start here, then see a doctor to be sure.
Start here to learn about Pilonidals! Who is at risk? Why does your tailbone hurt? Get the facts and be in the know.
Do you have a Pilonidal?
Check your symptoms here.