Pilonidal Sinus and Hidradenitis Suppurativa: What a Past Tailbone Cyst Can Mean

If you have ever had a painful cystCyst: A fluid- or keratin-filled sac under the skin. In Acne Inversa some lesions resemble epidermoid cysts but differ histologically. The term is used loosely in clinical practice.CystA fluid- or keratin-filled sac under the skin. In Acne Inversa some lesions resemble epidermoid cysts but differ histologically. The term is used loosely in clinical practice.Read more in the glossary, abscessAbscess: An inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.AbscessAn inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.Read more in the glossary, or draining tunnelDraining Tunnel: A sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Draining TunnelA sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Read more in the glossary near your tailbone, you may have been told it was a pilonidal sinus — sometimes called a pilonidal cyst. It may have been drained once, years ago, and never come back. Or it may have needed surgery.

Either way, it is worth remembering — because if you later develop recurring painful lumps in your armpits, groin, under your breasts, or elsewhere on your buttocks, that old pilonidal history can be a genuinely useful thing to mention.

Research shows a strong association between pilonidal sinus diseasePilonidal Sinus Disease: Chronic inflammation, abscesses, and tunnels at the top of the buttock crease, often triggered by an ingrown hair. Frequently co-exists with Acne Inversa.Pilonidal Sinus DiseaseChronic inflammation, abscesses, and tunnels at the top of the buttock crease, often triggered by an ingrown hair. Frequently co-exists with Acne Inversa.Read more in the glossary and hidradenitis suppurativa (HS). That does not mean everyone with a pilonidal sinus has HS, or ever will. It means a previous pilonidal sinus is relevant medical history when the rest of the picture also fits HS — and current evidence suggests it can sometimes show up before HS is recognised, not just alongside it.

Educational content only. This article explains the association between pilonidal sinus disease and HS, and what it does and does not mean. It cannot tell you whether you have either condition — only an examination can do that — and it does not replace pilonidal-specific surgical or coloproctological advice.

Key takeaways

• Pilonidal sinus disease and HS are strongly associated — a 2023 meta-analysis of five controlled studies put the pooled odds at roughly 6.5 times higher in people with HS than in people without.
• A single pilonidal sinus, on its own, is not evidence of HS. The association only becomes clinically useful when other HS-type symptoms are also present.
• Pilonidal disease can precede an HS diagnosis. Researchers studying an HS cohort proposed it as a possible sentinel event — a clue worth acting on, not proof of anything.
• The two conditions are anatomically and clinically distinct enough that current guidelines manage them separately, even when they occur in the same person.
• The single most useful thing you can do with this information is simple: mention both histories in the same appointment, rather than treating them as unrelated events.

What a pilonidal sinus actually is

A pilonidal sinus is a small pit, tunnelSinus Tract: A tunnel-like channel under the skin that forms between abscesses or nodules. Sinus tracts indicate more advanced disease and can chronically drain fluid. They are associated with Hurley Stages II and III.Sinus TractA tunnel-like channel under the skin that forms between abscesses or nodules. Sinus tracts indicate more advanced disease and can chronically drain fluid. They are associated with Hurley Stages II and III.Read more in the glossary, or cavity that typically develops in the upper part of the cleft between the buttocks, near the coccyx. Hair and mechanical friction in that area are thought to play a central role. Some pilonidal sinuses stay symptom-free for years. Others become inflamed and produce swelling, an abscess, pain, bleeding, or drainage, and some go on to recur or dischargeDischarge / Exudate: Fluid coming from an Acne Inversa lesion or tunnel. Can be clear (serous), bloody (sanguineous), pus-like (purulent), or a mix.Discharge / ExudateFluid coming from an Acne Inversa lesion or tunnel. Can be clear (serous), bloody (sanguineous), pus-like (purulent), or a mix.Read more in the glossary chronically.

On its own, that description already sounds similar to HS — both involve hair folliclesHair Follicle: The tube-shaped pocket in the skin from which a hair grows. In Acne Inversa, the follicle becomes plugged and eventually ruptures, spilling its contents into surrounding tissue and triggering the inflammatory cascade that defines the disease.Hair FollicleThe tube-shaped pocket in the skin from which a hair grows. In Acne Inversa, the follicle becomes plugged and eventually ruptures, spilling its contents into surrounding tissue and triggering the inflammatory cascade that defines the disease.Read more in the glossary, friction-prone skin, and can produce abscesses and chronic drainage. The similarity is real. It is also not the whole picture.

How pilonidal disease and HS actually differ

The clearest starting distinction is where symptoms occur and how they spread.

Pilonidal disease is typically centred on the upper intergluteal cleft, close to the tailbone. It usually presents as one or more small midline pits, an acute abscess, or a sinus that drains from roughly the same spot.

HS is a chronic inflammatory follicular condition. It tends to produce recurring nodulesNodule: A firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.NoduleA firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.Read more in the glossary, abscesses, tunnels, and scarring across several typical fold sites — armpits, groin, inner thighs, under the breasts, buttocks, and the perianal region — rather than staying confined to one midline point.

A single pilonidal sinus with no other symptoms does not, by itself, point to HS. Our comparison of Acne Inversa and pilonidal sinus walks through that anatomical distinction in more detail, including where symptoms on the buttocks specifically can go either way. This article covers different ground: not “which one is it,” but “does having had one matter for the other.”

How strong is the association, really?

According to PubMed, a 2023 systematic review and meta-analysis by Wark and colleagues, published in the British Journal of DermatologyDermatology: The medical specialty concerned with diagnosing and treating skin conditions. Acne Inversa is often managed by dermatologists, although surgery and other specialties may also be involved.DermatologyThe medical specialty concerned with diagnosing and treating skin conditions. Acne Inversa is often managed by dermatologists, although surgery and other specialties may also be involved.Read more in the glossary, pooled five controlled studies comparing pilonidal sinus disease in people with HS against people without it (DOI: 10.1093/bjd/ljac166). Pilonidal disease occurred significantly more often in the HS group, with a reported pooled odds ratio of 6.54 (95% CI 4.73–9.03).

That figure is worth reading carefully. An odds ratio compares two groups — it is not an individual’s personal risk. “6.5 times higher odds” does not mean “a 6.5-fold chance of developing HS if you’ve had a pilonidal sinus.” It means that, across the pooled studies, pilonidal disease was considerably more common among people who already had HS than among people who did not.

A separate, earlier cross-sectional study of 2,465 HS patients across multiple centres found that 27% reported lesions in the intergluteal fold, and that this group tended to have smokers and more severe HS overall (Benhadou et al., British Journal of Dermatology, 2019). Different study design, same direction of signal: the overlap is consistent, not a one-off finding.

Does a pilonidal sinus mean I have HS?

No — and this is the limit that matters most.

Pilonidal disease is common enough on its own that most people who have had one will never develop HS. A single pilonidal sinus is not an HS diagnostic criterion, and this article is not suggesting it should be treated as an early-warning test.

What changes the picture is context. A previous pilonidal sinus becomes more relevant when you also have:

• recurring painful nodules in typical HS locations (armpits, groin, under the breasts, buttocks)
• lesions that keep returning to the same folds
• tunnels under the skin, or characteristic scarring
• repeated drainage that isn’t explained by a single acute event

None of those, individually, proves HS either. The pattern across all of them — including the pilonidal history — is what’s worth describing in full during an assessment.

Can pilonidal disease appear before HS is diagnosed?

Yes, and this is the part of the evidence that makes the topic worth a dedicated page rather than a footnote.

A Spanish study examined 839 people already diagnosed with HS at two tertiary HS clinics. According to PubMed, pilonidal sinus disease had occurred in 32.6% of them (269 people), and having had pilonidal disease was associated with an earlier HS onset, a higher Hurley stageHurley Stage: A clinical classification system for assessing the severity of Acne Inversa in three stages: Stage I (single abscesses without sinus tracts), Stage II (recurrent abscesses with isolated sinus tracts), Stage III (extensive sinus tracts and scarring across an entire region). Named after Dr. Helen Hurley.Hurley StageA clinical classification system for assessing the severity of Acne Inversa in three stages: Stage I (single abscesses without sinus tracts), Stage II (recurrent abscesses with isolated sinus tracts), Stage III (extensive sinus tracts and scarring across an entire region). Named after Dr. Helen Hurley.Read more in the glossary, an inflammatory phenotype, and more fistulasFistula: A specific kind of tunnel that connects an inflammatory cavity to the skin surface, allowing chronic drainage. In HS literature, 'draining tunnel' and 'fistula' are often used interchangeably.FistulaA specific kind of tunnel that connects an inflammatory cavity to the skin surface, allowing chronic drainage. In HS literature, 'draining tunnel' and 'fistula' are often used interchangeably.Read more in the glossary and perianal involvement (Ureña-Paniego et al., Acta Dermato-Venereologica, 2023, DOI: 10.2340/actadv.v103.6569). The authors also found that a longer gap between the pilonidal episode and the HS diagnosis was associated with greater disease severity, and they proposed pilonidal sinus disease as a possible sentinel event — an early signal that could prompt closer HS assessment and follow-up in the right context.

Two limits are worth being direct about. First, 32.6% describes a tertiary HS clinic cohort — people already diagnosed with HS at specialist centres — not the general population, and not everyone who has ever had a pilonidal sinus. Second, this is a cross-sectional, observational finding. It cannot prove that recognising pilonidal disease earlier changes how HS is eventually treated, only that the two histories are meaningfully connected.

What it does support is narrower and still useful: if you’ve had a pilonidal sinus and you’re now being assessed for possible HS, that earlier episode is legitimate history to bring up — not an unrelated detail from a different part of your medical file.

Why might the two conditions be connected?

There isn’t one settled mechanistic answer yet. Both conditions involve hair follicles, friction-exposed skin, chronic inflammation, and — once established — tunnel and sinus formation. Historically, pilonidal disease, HS, acne conglobataAcne Conglobata: A severe, scarring form of nodulocystic acne, usually on the back, chest, and buttocks. Shares mechanistic and immunological overlap with Acne Inversa.Acne ConglobataA severe, scarring form of nodulocystic acne, usually on the back, chest, and buttocks. Shares mechanistic and immunological overlap with Acne Inversa.Read more in the glossary, and dissecting cellulitis of the scalp were grouped together as the “follicular occlusion tetradFollicular Occlusion Tetrad: A historical grouping of four conditions thought to share follicular plugging as the underlying mechanism: (1) Acne Inversa / HS, (2) acne conglobata, (3) dissecting cellulitis of the scalp, and (4) pilonidal sinus disease. Patients sometimes have more than one of the four.Follicular Occlusion TetradA historical grouping of four conditions thought to share follicular plugging as the underlying mechanism: (1) Acne Inversa / HS, (2) acne conglobata, (3) dissecting cellulitis of the scalp, and (4) pilonidal sinus disease. Patients sometimes have more than one of the four.Read more in the glossary,” on the idea that they shared an underlying mechanism.

Some researchers have gone further and proposed that pilonidal disease occurring in the intergluteal fold may represent a localised expression of HS itself, within the wider follicular-occlusion spectrum, rather than a fully separate disease. A recent histological comparison found that pilonidal and HS lesions share several immune and epithelial features despite differing in some respects — more intralesional hair and higher iron content in pilonidal tissue, for instance (Lagman & Criswell, Biotechnic & Histochemistry, 2025). That is active research, not a closed question.

For a patient, none of this needs resolving. Current European surgical guidance still manages pilonidal disease as its own distinct clinical problem (Ojo et al., British Journal of Surgery, 2024). You do not need to decide whether your pilonidal sinus “is really HS” — describing both histories accurately is what matters, and the clinical examination determines how each is classified.

What to mention — and how

The relationship works in both directions, so it’s worth thinking about which side you’re on.

If you already have HS: mention any previous tailbone pits, swelling at the top of the buttock cleft, repeated drainage from that same midline area, or previous pilonidal surgery — even if it happened years before your HS symptoms started.

If you’ve had pilonidal disease: consider raising HS specifically if you also get recurring lumps in the armpits or groin, lesions under the breasts, multiple affected buttock sites, recurring tunnels or drainage, or scarring you can’t otherwise explain.

A useful, low-pressure way to phrase it: “I previously had a pilonidal sinus near my tailbone. I’ve also been getting these recurring painful lumps elsewhere. I understand the two can sometimes be connected — could that be relevant here?” That gives a clinician real information without asking you to self-diagnose either condition.

Treatment stays separate

This is worth being explicit about, because it’s the easiest part of this topic to get wrong.

Having HS does not mean your pilonidal sinus will resolve on HS treatment. There is not enough evidence to support the idea that HS biologicsBiologic: A class of medications derived from living cells that target specific components of the inflammatory process. For Acne Inversa, biologics such as adalimumab and secukinumab are used when other treatments are insufficient.BiologicA class of medications derived from living cells that target specific components of the inflammatory process. For Acne Inversa, biologics such as adalimumab and secukinumab are used when other treatments are insufficient.Read more in the glossary or other systemic HS treatments generally treat pilonidal disease — pilonidal management is decided on its own anatomical and clinical grounds. Likewise, pilonidal surgery treats the pilonidal sinus; it does not treat HS elsewhere on the body.

A few specific things not to assume:

• An asymptomatic pilonidal sinus does not automatically need surgery. Watchful waiting is a reasonable approach when there’s no infection or troubling symptoms.
• An acute, painful pilonidal abscess is usually still drained when clinically needed — that decision is not overridden by an HS diagnosis, and shouldn’t be delayed because you assume a buttock lesion is “just your HS.”
• Recurrent pilonidal disease has more than one accepted surgical approach, and current European guidance reflects a shift toward individualised, sometimes less invasive options rather than one universal operation. That decision belongs with a surgical or coloproctological assessment, not with an HS article.

If you have both conditions, coordinated but distinct care — dermatology for HS, surgery or coloproctology for pilonidal disease — is a reasonable thing to ask for.

What the evidence does not show

It’s worth stating plainly what the research summarised here does not establish, because the association is easy to overstate:

• It does not show that every pilonidal sinus is HS, or vice versa.
• It does not show that pilonidal disease causes HS, or that HS causes pilonidal disease.
• It does not show that someone with a pilonidal sinus will go on to develop HS.
• It does not show that HS medication treats pilonidal disease, or that pilonidal surgery treats HS.
• It does not support screening imaging or a surgical referral for every person with HS who has no pilonidal symptoms.

What to bring to an appointment

You don’t need a long written history — a short timeline is usually more useful than a single photo of today’s lesion:

Age 19 — pilonidal sinus drained surgically near the tailbone. Age 22 — recurring painful lumps began in the groin. Age 24 — similar lesions started appearing in both armpits. Now — some lesions keep recurring and have left scarring.

That sequence gives a clinician more to work with than either event described on its own. Our diagnosis guide walks through how to prepare a fuller version of this, and the symptom tracker can help you keep the locations and dates organised as you go. If perianal symptoms and gastrointestinal symptoms (persistent diarrhoea, abdominal pain, rectal bleeding) occur together, that combination is a separate, important differential covered in our HS and Crohn’s disease guide — worth reading alongside this one rather than instead of it.

The bottom line

Pilonidal sinus disease and hidradenitis suppurativa are strongly associated — a pooled odds ratio of roughly 6.5 from a 2023 systematic review and meta-analysis, and a large HS cohort in which a previous pilonidal sinus tracked with earlier-onset, more severe disease. Neither finding means a pilonidal sinus is an HS diagnosis on its own.

The practical value is in connecting the history. If you’ve had a pilonidal sinus and you also get recurring painful lumps, drainage, or scarring in typical HS locations, say so — together, in the same appointment. An old “cyst near the tailbone” may be more relevant now than it looked at the time.

→ Use the diagnosis guide to prepare for that conversation