When Symptoms “on the Backside” Are Not Clear-Cut
Pain, dischargeDischarge / Exudate: Fluid coming from an Acne Inversa lesion or tunnel. Can be clear (serous), bloody (sanguineous), pus-like (purulent), or a mix., or an 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. on the buttocks is often quickly filed away under a single umbrella term in everyday life. For a medical classification, however, it makes a difference whether mainly the tailbone and gluteal cleft region is affected or whether a broader recurring HS pattern is present.
What Is More Consistent with a Pilonidal Sinus
A pilonidal sinus, often also referred to as a tailbone fistulaFistula: 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., typically affects the region of the gluteal cleft near the tailbone. It can remain symptom-free, develop an acute abscess, or chronically discharge secretion.
If symptoms repeatedly occur in exactly this region, a pilonidal sinus definitely belongs in a medical evaluation.
What Is More Suggestive of Acne Inversa
HS can occur on the buttocks, perianally, or perineally. The suspicion grows stronger when other typical HS features are also present:
- recurring deep 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. or abscesses,
- additional affected regions such as the armpits, groin, or skin folds under the breasts,
- scars, indurations, or tunnelsSinus 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 tracts) following repeated inflammation,
- a course that is not limited to a single spot in the gluteal cleft.
Overlaps are also possible. For this reason, “either/or” is not always the best initial assumption.
A previous pilonidal sinus is also worth remembering even after it has healed: research shows it is strongly associated with HS and can precede an HS diagnosis, which makes it useful history to mention if a recurring HS-type pattern shows up elsewhere later.
Why the Exact Location Helps
For the consultation, “on the backside” is often too imprecise. It is more helpful to consider:
- Is the spot in the central gluteal cleft near the tailbone?
- Is it more toward the side of the buttocks, perianal, perineal, or in several regions?
- Are there similar lesions in the armpits, groin, or under the breasts?
- Do openings, scars, or recurring weeping areas remain?
These questions do not replace an examination. They make the findings more precise for the examination.
Who Should Classify This?
Recurring symptoms in the tailbone region may require surgical or coloproctological evaluation. If an HS pattern is also possible at the same time, dermatological classification is important. In the case of severe pain, fever, or rapidly increasing inflammation, the area should be medically assessed promptly.
Terms explained in this article
Quick definitions of the key medical terms. Select any term for its full glossary entry.
- Discharge / Exudate
- Fluid coming from an Acne Inversa lesion or tunnel. Can be clear (serous), bloody (sanguineous), pus-like (purulent), or a mix.
- Abscess
- 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.
- Fistula
- 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.
- Nodule
- 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.
- Sinus 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.
FAQ
Can acne inversa and a pilonidal sinus occur in the same person?
Yes, overlap is possible, and a past pilonidal sinus is associated with a higher likelihood of HS. Having one condition does not rule out the other, which is why both should be considered during a medical evaluation.
What is the main location difference between the two conditions?
A pilonidal sinus typically centers on the gluteal cleft near the tailbone. Acne inversa can also affect this area but often involves additional sites such as the armpits, groin, or skin folds under the breasts.
Does a healed pilonidal sinus still matter for future HS evaluation?
It can be useful history to mention. Research suggests a previous pilonidal sinus is strongly associated with HS and may precede a later HS diagnosis, so it is worth raising if new recurring symptoms appear elsewhere.
Who should assess recurring symptoms near the tailbone?
Recurring tailbone-region symptoms may call for surgical or coloproctological assessment, while a possible HS pattern warrants dermatological input. Severe pain, fever, or rapidly worsening inflammation should be evaluated promptly.
References
- S2k-Leitlinie zur Therapie der Hidradenitis suppurativa / Acne inversa AWMF, 2024
- S3-Leitlinie Sinus pilonidalis, Version 3.0 AWMF, 2026
- North American clinical management guidelines for hidradenitis suppurativa, Part I Journal of the American Academy of Dermatology, 2019
