What Is a Pilonidal Dimple and How Is It Treated?

A pilonidal dimple is a small depression or pit in the skin at the top of the cleft between the buttocks, near the tailbone. On its own, it is not a disease. But this seemingly minor skin feature can become the entry point for loose hair fragments that burrow into the tissue beneath, triggering a painful condition called pilonidal sinus disease. Most people with a shallow dimple in this area never develop problems, yet for those who do, the condition brings recurring infections, abscesses, and sometimes a surprisingly large toll on daily life. Understanding when a dimple is harmless and when it signals trouble is the practical question most people searching this term are trying to answer.

What a Pilonidal Dimple Actually Is

The word “pilonidal” comes from Latin roots meaning “nest of hair,” and the name is apt. The dimple itself is just a shallow pit in the natal cleft, the crease between the buttocks just above the coccyx. Many people have one from birth or develop one during puberty. The dimple becomes medically relevant when hair, dead skin cells, and debris get trapped inside it. Over time, this material can form a sinus, which is a small tunnel or tract beneath the skin. When bacteria colonize that tunnel, the result is an abscess: a swollen, red, painful lump that often drains pus.

It is worth knowing that a pilonidal dimple and a sacral dimple are not the same thing, though the terms get confused. Sacral dimples are typically noticed in newborns during routine examinations, and the main concern with those is whether they signal an underlying spinal abnormality. A pilonidal dimple, by contrast, is the starting point for an acquired condition that overwhelmingly affects teenagers and young adults. The distinction matters because the medical workup and implications are completely different.

How Hair Gets Involved

The prevailing explanation for pilonidal disease centers on loose hair fragments penetrating the skin. Researchers have found that cut hair with sharp, rootless ends collects inside pilonidal sinus cavities in large quantities, and these fragments look morphologically like short head hair rather than body hair from the surrounding area.¹ This finding surprised many clinicians, who had long assumed the problem was caused by the patient’s own local body hair growing inward.

Further research measured the physical strength of hair in patients with pilonidal disease compared to matched controls. Occipital hair (from the back of the head) showed about 20% greater vertical penetrating force in affected patients, while hair in the intergluteal fold itself was roughly twice as strong as in controls.² Because occipital hair exerted the greatest force and cut fragments were found abundantly in pilonidal nests, the data suggest that hair falling from the back of the head during haircuts or daily shedding plays a bigger role than many people realize. This is one reason barbers and hairdressers are sometimes advised to clear cut hair from the neck and upper back promptly.

Who Gets Pilonidal Disease and Why

Pilonidal disease is not equally distributed across the population. It peaks in people between their late teens and early thirties, is more common in men, and has well-documented links to a few modifiable risk factors. Being overweight is one: studies consistently show a higher body mass index raises the odds, with one large case-control analysis finding an adjusted odds ratio of about 1.3 per unit increase in BMI.³ Excess weight deepens the natal cleft, increases moisture and friction, and creates a more hospitable environment for hair entrapment.

Prolonged sitting is the other major culprit. In that same study, people who sat for more than six hours a day had about four times the odds of developing the disease compared to those who sat less.⁴ A separate analysis found that roughly half of pilonidal disease patients held seated occupations.⁵ The condition was famously nicknamed “jeep disease” during World War II because so many soldiers developed it after spending long hours sitting in military vehicles. That association has held up: military populations still show high rates, with one modern military cohort reporting overall recurrence and comorbidity rates above 27% and 34% respectively after treatment.

Other factors include having thick or coarse body hair, a deep natal cleft, poor local hygiene, and excessive sweating in the area. Family history matters too, though no single gene has been pinpointed. If you have a combination of these factors, keeping the area clean, dry, and free of loose hair is the most practical preventive step.

What Happens When It Gets Infected

An uninfected pilonidal dimple can sit quietly for years. The trouble starts when bacteria colonize the trapped hair and debris. The resulting infection is typically polymicrobial, meaning multiple types of bacteria are involved. Anaerobic bacteria (those that thrive without oxygen) dominate, particularly species of Bacteroides and anaerobic cocci. Among the aerobic bacteria, E. coli, Proteus, and Streptococcus species are the most commonly isolated.⁶ The mix of gut-associated organisms reflects the proximity to the perianal region.⁷

An acute pilonidal abscess is hard to miss. The area becomes swollen, hot, exquisitely tender, and often drains foul-smelling fluid. Some people spike a fever. The initial treatment is usually incision and drainage, which provides immediate relief but does not address the underlying sinus. Without further treatment, the cycle of infection, drainage, and reinfection is common, and this is where chronic pilonidal disease begins.

Pilonidal Dimples Versus Sacral Dimples in Babies

Parents who notice a small pit near their baby’s tailbone often land on the term “pilonidal dimple” while searching online, but what they are usually looking at is a sacral dimple. These are extremely common in newborns. The concern is not hair entrapment but whether the dimple connects to the spinal canal, which could indicate a condition called occult spinal dysraphism.

The reassuring news is that a simple, shallow sacral dimple located within the gluteal crease, with no other skin abnormalities nearby, carries a very low risk. A meta-analysis in JAMA Network Open found the pooled rate of occult spinal dysraphism was under 1% in infants with a simple dimple, compared to nearly 9% when the dimple was atypical (larger, higher on the back, or accompanied by other skin markers like a tuft of hair or a skin tag).⁸ Other research has confirmed that isolated simple dimples or pits are not useful markers of spinal abnormalities.⁹

When additional skin markers are present alongside the dimple, the calculus changes. Infants with two or more markers, such as a dimple combined with a subcutaneous lump or a patch of discolored skin, show considerably higher rates of tethered cord and other abnormalities that sometimes require surgical release.¹⁰ Ultrasound is the standard first-line screening tool for babies under about six months, when the spine’s bony window is still open. If ultrasound shows anything suspicious, MRI follows.¹¹ For a baby with a lone, shallow, low-positioned dimple and no neurological symptoms, most pediatric guidelines recommend watchful observation rather than imaging.

Treatment Options for Pilonidal Disease

Once a pilonidal dimple has progressed to chronic or recurrent disease, treatment aims to eliminate the sinus tracts, remove trapped hair, and prevent recurrence. The options range from office-based procedures to major reconstructive surgery, and the right choice depends on how complex the disease has become.

Minimally Invasive Pit-Picking

For straightforward cases with one or a few sinus pits, pit-picking (sometimes called Bascom’s procedure) is often the first step. The surgeon excises the tiny pit openings and makes a small lateral incision to drain the sinus cavity. It can be done under local anesthesia in an office setting. In a study of adolescents, about 92% were symptom-free at an average follow-up of five months.¹² A randomized trial comparing pit-picking to radical excision found that pain levels in the first postoperative week were significantly lower with pit-picking, and wounds healed in a median of 17 days versus 60 days for excision.¹³ The trade-off is that pit-picking works best for less extensive disease and has a somewhat higher chance of needing a repeat procedure for complex cases.¹⁴

Endoscopic Treatment

A newer approach uses a small camera inserted into the sinus tract to visualize and destroy the cavity from the inside. One prospective series reported a median operative time of 18 minutes, a median hospital stay under seven hours, and a return to work within about five days.¹⁵ A systematic review found good healing rates, low recurrence, high patient satisfaction, and little time off work.¹⁶ As surgeons gain experience, outcomes improve further: one center’s recurrence rate dropped from about 23% in their early cases to around 5% as they moved past the learning curve.¹⁷

Phenol Injection

For patients who want to avoid surgery entirely, phenol injection is a chemical option. Crystallized phenol is applied directly into the sinus tract, destroying the lining tissue and causing the cavity to scar shut. Reported success rates range from about 60% to 95%, with complication rates under 2%.¹⁸ A meta-analysis comparing phenol to surgery found no significant difference in recurrence rates, but phenol had far fewer wound complications, shorter operating times, and a faster return to daily activities.¹⁹ Multiple applications are sometimes needed, but the procedure is quick and involves minimal downtime.

Flap Reconstruction for Complex or Recurrent Disease

When disease is extensive or has failed simpler treatments, surgeons may excise the entire affected area and close the wound using a tissue flap. The Karydakis flap and the Limberg (rhomboid) flap are the two most common techniques. Both shift the wound closure away from the midline, which flattens the natal cleft and removes the conditions that allowed hair to accumulate in the first place. In a study of 200 military patients, the Karydakis flap had a recurrence rate under 5%, compared to about 18% for standard midline closure.²⁰ A larger comparative study confirmed the pattern, with midline closure showing about 11% recurrence versus 3% for Karydakis flap and 8% for Limberg flap.²¹ The downside is a bigger operation with a longer recovery.

Laser Hair Removal as Prevention

Given that hair intrusion drives the disease, removing the hair makes intuitive sense as a preventive strategy. Laser epilation of the skin surrounding the natal cleft has been studied as an add-on treatment after surgery. Early observational work was promising but underpowered.²² A randomized clinical trial published in JAMA Surgery gave more definitive results: among adolescents and young adults, about 10% of those receiving laser epilation had a recurrence within one year, compared to roughly a third in the standard care group.²³ That is a meaningful reduction, and many surgeons now recommend laser treatments as a routine follow-up after pilonidal surgery, particularly for younger patients with thick hair.

Wound Care After Surgery

Pilonidal wounds are notoriously slow to heal, especially when left open to close from the bottom up (a technique called healing by secondary intention). Negative-pressure wound therapy, which involves placing a sealed dressing connected to a gentle vacuum over the wound, has been tested to see if it speeds things up. Results have been mixed. One randomized trial showed faster early healing in the first two weeks with vacuum therapy, but no significant difference in total time to complete wound closure (around 84 days for vacuum versus 93 for conventional dressings).²⁴ A more recent trial in adolescents found essentially equivalent outcomes between negative-pressure and conventional passive dressings for time to heal, return to school or work, and ability to sit normally.²⁵ So while vacuum dressings are not harmful, they do not seem to provide a clear advantage for most patients and add cost and complexity.

Regardless of dressing type, the practical advice is the same: keep the area clean, change dressings regularly, avoid prolonged sitting during recovery, and keep the surrounding skin free of hair (by shaving, depilatory cream, or laser). Wound checks with a clinician help catch early signs of infection or incomplete healing.

When a Pilonidal Dimple Looks Like Something Else

Not every lump or draining lesion near the tailbone is pilonidal disease. Hidradenitis suppurativa, a chronic inflammatory skin condition affecting hair follicles, can produce similar-looking abscesses and sinus tracts in the gluteal region. Ultrasound comparison studies have found that the two conditions share remarkably similar structural features, including saclike formations communicating with widened hair follicle bases. The key distinguishing finding is that pilonidal cysts contain a denser concentration of hair tract fragments within each structure.²⁶ Perianal abscesses and fistulas from other causes can also mimic pilonidal disease, which is why a careful clinical examination (and sometimes imaging) is important before choosing a treatment strategy.

The Mental Health Side

Pilonidal disease hits during some of the most socially sensitive years of life, and its impact goes well beyond the physical. Before treatment, adolescents reported that daily activities, sports participation, and school attendance were moderately or severely affected in a majority of cases. After minimally invasive treatment, those numbers dropped dramatically: the proportion with moderate or severe daily-activity limitations fell from about two-thirds to under 10%.²⁷ Quality of life scores improve significantly after successful surgery across multiple domains, including mood, fitness, social life, work, and sexual function.²⁸

A population-based cohort study took this further, finding a statistically significant association between pilonidal sinus disease and depression over a five-year follow-up. The link was strongest in women and in patients over 45.²⁹ Chronic pain, embarrassment about wound drainage, and repeated surgical procedures all plausibly contribute. If you are dealing with recurrent pilonidal problems and noticing a decline in your mood or social engagement, it is reasonable to bring that up with your doctor alongside the physical symptoms.

Rare but Serious Complications of Chronic Disease

The vast majority of pilonidal disease, even when recurrent and frustrating, remains benign. In exceedingly rare cases, however, long-standing chronic pilonidal sinuses can undergo malignant transformation, most commonly into squamous cell carcinoma. Case reports describe this complication in patients who have had untreated or repeatedly inflamed sinuses for many years, sometimes decades.³⁰ Warning signs include a chronic wound that refuses to heal, persistent foul discharge, and increasingly complex fistula tracts in someone with a long history of disease.³¹ Immunosuppression and human papillomavirus infection have been flagged as possible factors that could accelerate such a transformation.³² This is not something to lose sleep over, but it is a strong argument against simply ignoring a pilonidal sinus that keeps coming back year after year. Getting definitive treatment sooner removes the tissue that chronic inflammation could, in theory, eventually change.