Hidradenitis affecting the perineum

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Hidradenitis suppurativa is a chronic inflammatory disorder centred on the hair follicle. Recurrent painful nodules and abscess-like lesions can evolve into draining tunnels and scars in the axillae, groin, inframammary region, buttocks and perineum. It is not caused by inadequate washing and is not a sexually transmitted infection. Odour, leakage, friction and pain may nevertheless create profound embarrassment and avoidance. Ask about other affected folds, previous episodes, family history and the effect on daily living; otherwise, years of repeated treatment for isolated boils can pass before the inflammatory pattern is recognised.

Two related treatment problems must be separated. Active inflammation can improve with medication, but established tunnels and fibrotic damage may require a surgical procedure. The European treatment guideline therefore relates medical treatment to inflammatory activity and surgery to local structural disease. The August 2026 diagnostic guideline recommends dynamic IHS4 assessment and refined staging, while limiting classic Hurley staging to particular uses such as selecting a regional surgical approach. A meaningful review combines lesion counts with pain, discharge, function and the patient’s priorities, rather than assuming that a single severity label captures every aspect of disease.

Key points

HS combines typical recurrent inflammatory nodules, abscesses or tunnels with a typical flexural distribution; the 2026 guideline uses at least two lesions or episodes in six months as the recurrence criterion.
Assess acute infection separately and arrange urgent source control when needed; do not start anti-TNF treatment through uncontrolled local infection, abscess-related sepsis or active TB.
IHS4 equals inflammatory nodules plus twice the abscess count plus four times the draining-tunnel count: at most 3 is mild, 4–10 moderate and at least 11 severe.
Use dynamic inflammatory counts to monitor medical response and local tunnel/scar anatomy to choose surgery; classic Hurley stage alone is not a sensitive treatment-response measure.
Topical clindamycin is a selected off-label option for limited disease without draining tunnels; oral tetracyclines require a defined course and review rather than repeated unmeasured short prescriptions.
Adalimumab has a distinct adult HS loading schedule and a NICE 12-week response gate after inadequate conventional systemic therapy; do not substitute Crohn dosing.
Deroofing or excision can address persistent tunnels and damaged tissue; repeated incision and drainage relieves an acute collection but does not provide durable control of the underlying disease.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Follicular inflammatory disease

Follicular occlusion and rupture contribute to an inflammatory process in predisposed skin. Genetic, immunological and environmental factors interact; poor personal hygiene is not its cause.

Associated susceptibility

Family history, smoking, obesity and mechanical stress can accompany disease. Their contribution varies between individuals, and associations do not establish a single necessary trigger in every patient.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Inflammatory lesion formation
Follicular disruption promotes deep local inflammation, producing tender nodules and abscess-like lesions. Repeated activity can occur close to previous sites rather than as isolated unrelated infections.
2
Tunnel and scar evolution
Recurrent inflammation damages tissue and creates epithelialised tunnels and fibrosis. Structural lesions can persist after active inflammation declines, separating anatomical damage from current disease activity.
3
Microbial contribution
Colonisation and biofilms may complicate chronic tunnels, while secondary infection can add acute illness. The inflammatory disorder is not explained by a positive swab alone.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Recognise the recurring distribution

Look for deep tender nodules, recurrent abscesses, paired comedonal openings, tunnels and characteristic scars in typical folds. The 2026 clinical criterion combines characteristic lesions, location and recurrence of at least two lesions or episodes over six months. Inspect other sites with consent; a patient presenting with perineal pain may not volunteer a long history of axillary lesions.

Count current inflammation

Record the number of inflammatory nodules, abscesses and draining tunnels across the affected sites. IHS4 weights these by 1, 2 and 4 respectively. For example, two nodules and one draining tunnel yield 6, which is moderate even without an abscess. Non-draining scars are important structurally but are not counted as draining tunnels in this calculation.

Describe irreversible regional disease

Classic Hurley I describes abscesses without tunnels or scarring; II describes recurrent abscesses with separated tunnels and scars; III describes diffuse or near-diffuse interconnected disease across a region. These regional structural descriptions help a surgical discussion, but a fixed scar can persist while inflammation improves. Do not use an unchanged Hurley label to conclude that a medical treatment has failed.

Distinguish an anorectal communication

Superficial skin tunnels can be difficult to distinguish from a true fistula-in-ano around the anal verge. Ask about Crohn symptoms, examine the anal and rectal context when appropriate and involve colorectal expertise if the course suggests a sphincter-related tract. HS and IBD can coexist, so the presence of a convincing HS pattern elsewhere does not settle every perianal opening.

Measure the wider burden

Ask directly and without blame about pain, sleep, dressing requirements, odour, intimacy, work and mental health. Review smoking, weight and cardiometabolic risk, and enquire about bowel and inflammatory joint symptoms. The new guideline recognises important comorbidities but does not show that addressing every associated factor necessarily changes the HS course; offer support for its own health value as well.

Recognise a lesion that has changed

New focal induration, persistent ulceration, bleeding or a growing mass within longstanding perineal disease warrants specialist assessment for squamous malignancy. Ordinary recurrent inflammation and scarring can make a new lesion harder to appreciate. Record its location and evolution, and do not simply prescribe another antibiotic without examination.

Red flags requiring action

Rapidly progressive pain or systemic illness can represent superimposed infection rather than an ordinary inflammatory flare.
A persistent ulcer, enlarging mass or new bleeding in a chronically affected perineal area requires assessment and possible biopsy.
Perianal tunnels accompanied by diarrhoea, weight loss or rectal inflammation require assessment for coexisting Crohn disease.
Severe distress, hopelessness or suicidal thoughts need direct assessment and appropriate urgent support.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Clinical examination and a repeatable lesion mapFirst step
Why
Confirm the pattern and establish an objective inflammatory and structural baseline.
Interpretation and limitations
Diagnosis is usually clinical. Record lesion type and site, IHS4, pain and quality-of-life burden so that later improvement can be calculated from comparable observations. A skin culture does not diagnose HS and cannot replace the pattern of recurrence and typical morphology.
02
Microbiology when secondary infection is suspected
Why
Guide treatment of an unusually acute or infective presentation.
Interpretation and limitations
A rapidly expanding inflammatory area, fever or systemic illness raises concern for infection. Culture may guide targeted antibiotics, but colonisation in chronic drainage does not prove that bacteria are the primary cause of every flare. A fluctuant collection may still need drainage irrespective of a pending culture result.
03
Pelvic MRI and colorectal assessment when anatomy is uncertain
Why
Distinguish a deep anal fistula or Crohn-associated tract from skin-limited tunnels.
Interpretation and limitations
Imaging is selected for suspected sphincter involvement, deep extension, recurrent perianal abscess or conflicting clinical findings. It is not required to confirm every typical superficial HS lesion. Luminal assessment follows bowel symptoms and specialist judgement rather than an automatic colonoscopy for all patients with HS.
04
Biopsy of a suspicious persistent lesion
Why
Exclude malignancy or an alternative inflammatory diagnosis in atypical tissue.
Interpretation and limitations
Sample the lesion that is clinically concerning through the appropriate specialist pathway. A nonspecific inflammatory result from another site should not falsely reassure about a new ulcer or mass. Histology is particularly useful when morphology or evolution no longer fits the established pattern.
05
Treatment safety and comorbidity assessment
Why
Identify organ, infection and medication risks before systemic or biological treatment.
Interpretation and limitations
Review pregnancy potential, current medicines and relevant blood counts, renal and liver function. Before adalimumab, assess TB, HBV, vaccination, active infection, heart failure and neurological or malignancy history. Cardiometabolic and psychological assessment addresses common associated burden alongside the skin treatment.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Cryptoglandular fistula-in-ano

A tract related to an anal gland may connect the anal canal with perianal skin and cross sphincter tissue, unlike typical skin-centred HS tunnels.

Perianal Crohn disease

Penetrating inflammatory bowel disease can cause complex tracts, abscesses and rectal inflammation. It may coexist with HS and produce overlapping symptoms at the anal margin.

Recurrent bacterial abscesses

Staphylococcal infection can cause repeated boils, but the distribution, comedonal changes, tunnels and scarring of HS create a broader recurring inflammatory pattern.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Worked caseMeasured response after a conventional courseFirst stepA 29-year-old woman has recurrent painful groin and perineal nodules without draining tunnels.

1Examination finds three inflammatory nodules and no abscess or draining tunnel, giving IHS4 = 3, mild inflammatory disease. She reports repeated flares despite an adequate topical course. There is no spreading infection, bowel symptom or suspicious ulcer; the clinician records pain at 6/10 and the effect on sitting at work.
2After confirming no tetracycline allergy, pregnancy or breastfeeding, reviewing hepatic risk and interacting medicines, she chooses the PCDS July 2025 adult regimen: doxycycline 200 mg orally once daily, using two selected 100 mg capsules, initially for three months. She takes it upright with plenty of water, well before bedtime, and receives explicit advice on sun reactions, swallowing pain and significant diarrhoea.
3At the three-month review there is one inflammatory nodule and no abscess or draining tunnel, so IHS4 falls from 3 to 1. Pain is 2/10, she can sit through a working morning and has had no significant adverse effect. The observed response supports a treatment break, with a recorded plan to reassess recurrent flares rather than automatically renew antibiotics indefinitely.
4At the next agreed review she still has one intermittent small nodule and no new tunnel. Her dressing needs are minimal and she knows to return for two further flares, deteriorating control or new deep anal symptoms. The outcome is improved inflammatory control, not permanent eradication of a relapsing disorder; support for smoking or weight concerns remains available without making care conditional on either.

02EscalationPersistent moderate or severe inflammatory diseaseEscalationPainful lesions or draining tunnels remain despite an adequate conventional systemic treatment trial.

1Recheck diagnosis, actual adherence, treatment duration, lesion counts and whether an undrained infection or structural tunnel dominates. Refer to dermatology while continuing appropriate supportive care, especially with severe disease, scarring or substantial psychological effects. Avoid cycling through short empirical antibiotic courses without a measured endpoint.
2For eligible adults with active moderate or severe HS that has not responded to conventional systemic therapy, consider adalimumab through the specialist pathway. The HS regimen is 160 mg subcutaneously on day 1, 80 mg on day 15 and then 40 mg weekly or 80 mg every other week from day 29. Screen and control infection before initiation; use a suitable daily antiseptic wash on affected external skin as recommended by the product, with attention to tolerability and mucosal avoidance.
3At 12 weeks apply NICE TA392: continue only with at least a 25% reduction in the combined abscess and inflammatory-nodule count and no increase in either abscesses or draining fistulas. A total lesion reduction does not pass this gate if a draining-fistula count increases. Record pain, function and adverse effects alongside that count-based decision.
4If response is inadequate, review the next medical or surgical option in the specialist team. Other advanced treatments exist, including IL-17-directed agents, but suitability and evidence differ, particularly when IBD coexists. Do not extrapolate the selected adalimumab prescription to another product or treat all advanced agents as interchangeable.

03Structural treatmentPersistent tunnels or an acute collectionRegional tissue damage or a new fluctuant painful lesion becomes the dominant problem.

1DefinitiveAssess a tense acute collection for drainage and concurrent infection treatment. Incision and drainage can relieve immediate pain but leaves the underlying inflammatory tendency and tunnel architecture, so arrange a continuing medical or definitive surgical plan rather than presenting drainage as a cure.
2For limited persistent tunnels, discuss deroofing, which removes the tunnel roof while conserving surrounding tissue. More extensive interconnected disease can require excision with a planned wound-healing or reconstruction strategy. Define the involved skin and relationship to the anus before surgery, and involve colorectal or reconstructive colleagues when anatomy requires it.
3Explain healing time, pain, dressings, recurrence and the functional consequences of the proposed excision. Coordinate inflammatory treatment and surgery instead of assuming one must universally stop for the other. Decisions about biological treatment around an operation account for active infection and individual procedural risk; neither routine continuation through sepsis nor an arbitrary stop interval is appropriate.
4Follow the wound through actual healing and reassess residual or recurrent inflammatory lesions. Absorbent low-adhesive dressings and tissue-viability support can reduce friction and leakage burden. New ulceration, induration or bleeding in the treated or surrounding area requires examination rather than being attributed automatically to scar tissue.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

A topical option for limited inflammatory lesions; expected benefit for deep nodules or established tunnels is limited, so failure prompts reassessment rather than repeated blind extension.

Clindamycin 1% — Dalacin T 10 mg/mL topical lotion

Selected adult off-label HS use for mild-to-moderate superficial disease without draining tunnels: shake and apply a thin film to affected external skin twice daily during a flare, for up to 12 weeks under the European treatment guidance, then assess benefit and need. The selected UK product is licensed for acne, not HS.

Do not use with clindamycin/lincomycin or excipient allergy, a history of inflammatory bowel disease or antibiotic-associated colitis. Stop for significant or prolonged diarrhoea and assess possible colitis even though application is topical. Avoid eyes, mucosa and intrarectal use; local irritation can occur. Review neuromuscular-blocking medicines and use caution in atopic patients. First-trimester use is only if clearly needed; pregnancy and breastfeeding require individual benefit–risk discussion, including possible infant diarrhoea, blood in stool or rash. The topical SmPC supplies no renal/hepatic adjustment schedule; do not invent one or extend an adult HS regimen to children.

Conventional systemic treatment for inflammatory HS when selected after assessment, including inadequate topical control; review benefit, adverse effects and antibiotic exposure rather than prescribing indefinitely.

Doxycycline — Sovereign 100 mg oral capsules

Selected adult off-label HS regimen from PCDS July 2025: 200 mg orally once daily, initially for three months, then review lesions and consider a treatment break if improved. Use two 100 mg capsules with plenty of water while sitting or standing, well before retiring; food may reduce gastric irritation. HS use and course come from the clinical pathway, not the product’s acne indication.

Contraindicated in pregnancy, breastfeeding and tetracycline or excipient hypersensitivity. This is an adult HS regimen; do not extrapolate to a child. No renal dose adjustment is required at usual recommended doses, but hepatic impairment or other hepatotoxic medicines require caution and review. Avoid systemic retinoids such as isotretinoin because of intracranial-hypertension risk. Separate iron, zinc, bismuth and aluminium/calcium/magnesium-containing antacids as far as practical; monitor warfarin anticoagulation and ciclosporin if co-prescribed, and review enzyme inducers such as carbamazepine or phenytoin. Avoid methoxyflurane coadministration. Stop and seek assessment for severe rash, photosensitivity, significant diarrhoea or swallowing pain; headache with visual disturbance needs urgent assessment for raised intracranial pressure. Review myasthenia gravis and lupus risks before treatment.

Specialist anti-TNF treatment with the HS-specific loading and maintenance schedule; funding and continuing treatment follow the applicable NICE pathway and ongoing individual benefit–risk assessment.

Adalimumab — selected Humira 40 mg subcutaneous injection

Eligible adults with moderate-to-severe active HS after inadequate conventional systemic therapy: 160 mg subcutaneously on day 1 (four 40 mg injections that day, or two daily over two consecutive days), then 80 mg on day 15, then 40 mg weekly or 80 mg every other week from day 29. Use an appropriate daily topical antiseptic wash on external HS skin. Assess at 12 weeks: NICE continuation requires at least 25% fewer abscesses plus inflammatory nodules, with no increase in abscesses or draining fistulas.

Do not initiate with active infection until controlled; active TB, severe infection, relevant hypersensitivity and NYHA III–IV heart failure are contraindications. Screen TB/HBV, review vaccines and provide a patient reminder card; monitor infection during and for up to four months after treatment. Renal/hepatic impairment is unstudied with no dose recommendation; obtain specialist assessment. Use caution in mild heart failure, demyelinating disease, malignancy history and older adults. Stop for serious infection, severe allergy or worsening heart failure and assess significant cytopenia symptoms. Avoid live vaccines and combination with other biological DMARDs or TNF inhibitors such as anakinra or abatacept. Use in pregnancy only if clearly needed; consider contraception during treatment and five months after the final dose. Breastfeeding is permitted by this SmPC. For an infant exposed in utero, live vaccines are not recommended until five months after the mother’s last injection during pregnancy. Adult and adolescent HS schedules differ; do not substitute this adult prescription for paediatric specialist dosing.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Fibrosis and contracture

Repeated damage can produce thick scars, persistent tunnels and contracture. Anogenital involvement may affect movement, sexual function and the practical management of drainage.

Infection and lymphatic damage

Superimposed infection can cause acute systemic illness, while chronic inflammation and scarring can disrupt lymphatic drainage and contribute to regional swelling.

Psychosocial and malignant burden

Chronic pain and discharge can profoundly affect mental health and relationships. Squamous malignancy is an uncommon but consequential complication of longstanding disease, particularly at chronically affected perineal sites.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Recount inflammatory nodules, abscesses and draining tunnels using the same method at each treatment review; record IHS4 and structural tunnel or scar findings separately.
Ask about pain, new flares, leakage, dressings, sleep, intimacy and ability to work, because lesion improvement may leave important residual disability.
Review topical or oral antibiotic response at the specified course endpoint and check adverse effects; a repeat prescription needs a reason and an antimicrobial-exposure plan.
At the adalimumab 12-week review document the combined abscess/nodule reduction and each abscess and draining-fistula count, so the NICE continuation criterion can actually be checked.
During biological therapy assess infection, injection reactions, heart-failure symptoms, neurological change and blood abnormalities, and record product and batch traceability.
Reassess gastrointestinal, joint, cardiometabolic and psychological symptoms periodically; the 2026 guideline supports structured comorbidity review without treating association as proof of causation.
Examine a changed chronic lesion or a wound that fails to progress, especially persistent focal ulceration, a mass or bleeding, rather than repeatedly labelling it a flare.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Count before labelling severity

One draining tunnel alone contributes four points and therefore reaches moderate IHS4 disease. Conversely, old scars without active drainage do not add tunnel points, although they can still justify a structural surgical discussion.

NICE response is not HiSCR

The NICE adalimumab continuation threshold is at least 25% reduction in the combined abscess and inflammatory-nodule count with no increase in abscesses or draining fistulas. Do not replace it with a different research endpoint or ignore worsening tunnels because the combined count has fallen.

Source-specific dosing stays explicit

PCDS describes 200 mg once-daily doxycycline initially for three months, while European evidence also describes a twice-daily 100 mg study regimen. The selected worked prescription uses the stated UK pathway; neither should be mislabelled as the licensed acne dose.

Topical treatment can carry systemic cautions

Skin application does not eliminate clindamycin-associated diarrhoea or the selected product’s IBD contraindication. This is especially relevant in perineal disease, where coexisting Crohn disease may otherwise be overlooked.

Support without blame

Weight, smoking and friction can be relevant to an individual’s health and symptoms, but HS is an inflammatory disease and access to treatment should not depend on an assumption that the patient caused it. Offer practical support, comfortable dressings and clear routes for psychological help.

11Common pitfallsFrequent interpretation and management errors.

01
Treating recurrent typical fold lesions as unrelated boils without looking for tunnels, scars or disease at other sites.
02
Using classic Hurley stage alone to monitor inflammatory treatment response when scar architecture has not changed.
03
Giving topical Dalacin T to a patient with IBD because its route is assumed to remove all systemic contraindications.
04
Applying an adalimumab Crohn loading regimen to HS or renewing treatment without the 12-week count-based assessment.
05
Equating every positive drainage culture with the cause of HS, or missing true sepsis because chronic lesions often drain.
06
Repeating incision and drainage without arranging an inflammatory and structural treatment plan.

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