Hidradenitis Suppurativa vs. Acne Vulgaris: A Complete Clinical Comparison

Written by Dr. rer. nat. Dennis Alexander Kwiatkowski

Hidradenitis suppurativa (HS) and acne vulgaris are fundamentally different diseases that share only a superficial resemblance. While both involve hair follicles, they diverge in mechanism, location, severity, prognosis, and treatment. HS is a chronic, progressive autoinflammatory condition affecting intertriginous skin, driven by immune dysregulation involving TNF-α, IL-17, and IL-1β — whereas acne vulgaris is a disorder of sebaceous follicles driven by excess sebum, bacterial colonization, and localized inflammation. This distinction matters because HS patients face an average 7–10 year diagnostic delay, often being repeatedly misdiagnosed with “regular acne” or boils, leading to irreversible scarring and diminished quality of life. Three biologic therapies are now FDA- and EMA-approved specifically for HS, with a robust pipeline of oral and injectable agents entering the market through 2026–2027.

Two Diseases, Two Entirely Different Biological Mechanisms

Acne vulgaris is a disorder of the pilosebaceous unit — the hair follicle and its attached sebaceous gland. Four interlinked processes drive the disease: androgen-stimulated excess sebum production, abnormal follicular keratinization creating microcomedones, colonization by Cutibacterium acnes (which activates innate immunity via TLR-2 signaling), and the resulting localized inflammatory cascade involving IL-8 and IL-12. Crucially, C. acnes colonization is central to acne pathogenesis, and most acne treatments target this bacterium or the sebaceous gland directly.

HS originates in the terminal hair follicle within apocrine gland-bearing skin through an entirely different sequence. Follicular hyperkeratosis causes plugging, which leads to follicle dilation, cyst formation, and eventual rupture into the dermis. This rupture triggers a massive autoinflammatory response dominated by TNF-α, IL-1β, and IL-17A/F, with Th1/Th17 immune polarization, regulatory T-cell deficiency, and B-cell/plasma-cell infiltration. Unruptured HS lesions are sterile — bacteria are secondary colonizers, not primary drivers — which is why antibiotics provide only temporary relief. This is also why acne inversa is not contagious, despite frequent misconceptions to the contrary. Over time, chronic inflammation produces dermal fibrosis and epithelialized sinus tracts (tunnels), a hallmark feature never seen in typical acne. Genetic mutations in gamma-secretase subunit genes (NCSTN, PSEN1, PSENEN) affecting the Notch signaling pathway have been identified in approximately 5% of HS patients, and about one-third report affected first-degree relatives.

Where Each Condition Appears on the Body

The anatomical distributions are nearly opposite, which is why HS is sometimes called “acne inversa.” Acne vulgaris affects sebaceous gland-rich areas: primarily the face (nearly universal), upper chest, upper back, shoulders, and neck. The face alone has approximately 800 sebaceous glands per cm², making it the epicenter of the disease.

HS affects intertriginous (skin-fold) areas where apocrine glands and terminal hair follicles are concentrated. The most commonly affected sites are the axillae (most common in both sexes), inguinal and groin folds (more common in women), inframammary folds (women), perianal and perineal regions (more common in men), gluteal area, and inner thighs. Less commonly, HS may involve the mons pubis, sub-abdominal folds, or retroauricular area. Mechanical friction, occlusion, and sweating in these intertriginous zones promote follicular occlusion and amplify IL-17-mediated immune responses.

How the Lesions and Symptoms Differ

Acne presents across a well-defined spectrum from non-inflammatory to inflammatory. Non-inflammatory lesions include open comedones (blackheads) and closed comedones (whiteheads). Inflammatory lesions range from small papules and pustules to larger nodules and cysts in severe nodulocystic acne. The hallmark precursor is the microcomedo. Lesions are generally superficial to moderately deep, and while severe acne causes scarring, it does not produce interconnected tracts beneath the skin.

HS presents with fundamentally different, deeper, and more destructive lesions. The earliest manifestation is a deep-seated, painful nodule (0.5–2 cm) that persists for days to months. These progress to fluctuant abscesses that may rupture spontaneously, draining purulent and often malodorous fluid. The pathognomonic feature of HS is the sinus tract (tunnel) — an epithelial-lined channel connecting deep lesions through the dermis, which drains chronically. Progressive fibrosis creates hypertrophic scarring that can restrict range of motion. Over 50% of HS patients experience prodromal symptoms (burning, stinging, warmth) 12–48 hours before a new lesion appears — one of several early warning signs to watch for. HS is significantly more painful than acne and produces chronic malodorous discharge that profoundly affects daily life.

How HS Severity Is Classified

Two complementary systems are now recommended by the 2024/2025 European S2k guidelines:

Hurley staging (for the non-inflammatory/structural component) classifies irreversible tissue damage per body region. Stage I (approximately 68–70% of patients at presentation) involves abscess formation without sinus tracts or scarring. Stage II (approximately 28% of patients) features recurrent abscesses with sinus tract formation and scarring, with normal skin separating lesions. Stage III (2–4% of patients) involves diffuse or near-diffuse involvement with multiple interconnected sinus tracts across an entire area.

IHS4 scoring (for the inflammatory/active component) provides a dynamic, treatment-responsive measure calculated as: (nodules × 1) + (abscesses × 2) + (draining tunnels × 4). Scores of ≤3 indicate mild disease, 4–10 moderate, and ≥11 severe. Unlike Hurley staging, IHS4 can track improvement with treatment.

Who Gets Each Condition and What the Disease Course Looks Like

Acne vulgaris is extraordinarily common, affecting roughly 85% of people between ages 12 and 25. It typically begins at puberty, peaks at ages 15–19, and often improves spontaneously with age by the third decade. Adolescent acne is slightly more common in males; adult and late-onset acne disproportionately affects women. While acne causes meaningful psychological distress and scarring, it generally follows a self-limiting trajectory.

HS is far less common, with a true prevalence estimated at 0.1–1% of the population (a 2021 JAMA Dermatology meta-analysis estimated 0.4%). It typically begins in the second or third decade of life (mean age at first symptoms: 24.6 years) and shows a clear 3:1 female-to-male ratio in Western populations. Black and African American patients face 2–3 times higher incidence and greater disease severity than White patients. Unlike acne, HS is a chronic, relapsing, progressive condition that does not spontaneously resolve. Key risk factors include smoking (OR 2.72), obesity (mean BMI of 36.1 in one cohort), and family history.

HS carries an extensive comorbidity burden that acne does not. Metabolic syndrome (OR 2.19), type 2 diabetes, inflammatory bowel disease (Crohn’s disease risk 3× greater than controls), cardiovascular disease, and psychiatric illness (depression prevalence up to 43%; suicide risk OR 2.08) are all significantly associated. HS patients report DLQI scores of 8.3–16.9, consistently higher than psoriasis patients, making HS potentially the dermatological condition with the greatest quality-of-life impact.

The 7-Year Diagnostic Gap and Why HS Is So Often Missed

The average diagnostic delay for HS is 7–10 years — a figure remarkably consistent across international studies. The PIRANHA study (Germany, 394 patients) documented a mean delay of 10.0 years, with first symptoms at age 24.6 and diagnosis at age 34.6. A 2015 global multicenter study (517 patients, 24 countries) found 73.3% of HS patients experienced more than a 2-year diagnostic delay. Before receiving a correct diagnosis, patients typically consult more than 3 different physicians and receive more than 3 incorrect diagnoses. Common misdiagnoses include boils/furunculosis (the most frequent), folliculitis, acne vulgaris, infected cysts, and recurrent abscesses.

Several factors drive this delay. Early HS nodules closely resemble boils or folliculitis. The disease affects intimate, hidden body areas that patients may be reluctant to show. Many clinicians — including dermatologists — have limited familiarity with HS. There is no confirmatory laboratory test. Racial disparities compound the problem: non-White patients are significantly more likely to experience delayed diagnosis. The consequences are severe: longer delay correlates with higher Hurley stage at diagnosis, more surgical interventions, more comorbidities, and reduced response to medical treatment. Experts describe a “window of opportunity” for early intervention that closes as the disease progresses to irreversible scarring and tunneling — making it essential to recognize HS before it progresses.

Treatment: From Topical Creams to Injectable Biologics

The treatments for these two conditions have almost no overlap, underscoring their biological differences. Acne vulgaris responds to therapies targeting sebum, bacteria, and keratinization: topical retinoids (tretinoin, adapalene), benzoyl peroxide, topical antibiotics (clindamycin), oral antibiotics (doxycycline, minocycline), hormonal therapy (spironolactone, oral contraceptives), and isotretinoin for severe disease. Notably, isotretinoin — the most powerful acne treatment — has limited to no efficacy in HS, serving as an important clinical distinguishing factor.

HS requires an entirely different, multimodal approach:

• Antibiotics serve as first-line treatment for mild-to-moderate disease: oral tetracyclines and topical clindamycin for localized Hurley Stage I disease
• Biologic therapies are indicated for moderate-to-severe inflammatory HS (three approved agents, detailed below)
• Surgical intervention addresses irreversible structural damage: incision and drainage for acute abscesses, deroofing for sinus tracts (Hurley II), and wide local excision for diffuse disease (Hurley III)
• Adjunctive measures include weight management, smoking cessation, pain management, and wound care

The 2024/2025 European S2k guidelines now recommend a holistic combined approach: medical therapy (biologics) to control active inflammation alongside surgery to remove irreversible tissue damage. Treatment decisions are guided by disease form — IHS4 severity for inflammatory disease, Hurley staging for structural disease.

Three FDA- and EMA-Approved Biologics for HS

Adalimumab (Humira) — a TNF-α inhibitor — became the first-ever approved therapy for HS in 2015 (EMA July 2015; FDA September 2015). The PIONEER I and II trials (633 patients, published in NEJM 2016) demonstrated HiSCR50 response rates of 42–59% versus 26–28% for placebo at week 12. It is approved for adults and adolescents ≥12 years. Multiple biosimilars are now available.

Secukinumab (Cosentyx) — an IL-17A inhibitor — was the second approved biologic (EMA June 2023; FDA October 2023), based on the SUNSHINE and SUNRISE trials (over 1,000 patients, published in The Lancet 2023). HiSCR50 rates at week 16 ranged from 42–46% (every-2-week dosing) versus 31–34% placebo, with sustained responses of 55–63% at week 52. In March 2026, the FDA expanded the indication to patients aged ≥12 years.

Bimekizumab (Bimzelx) — the first dual IL-17A/F inhibitor — was the third approval (EMA April 2024; FDA November 2024), based on the BE HEARD I and II trials (1,014 patients, published in The Lancet). HiSCR50 rates at week 16 were 48–52% versus 29–32% placebo. Three-year extension data showed impressive durability: HiSCR75 sustained in 81% of year-1 responders, and HiSCR100 (complete response) in 50% at three years.

What Is New in 2024–2026: A Rapidly Evolving Landscape

The HS therapeutic landscape has transformed dramatically. Beyond the bimekizumab approval and secukinumab pediatric expansion, several major developments are reshaping the field.

Povorcitinib, an oral selective JAK1 inhibitor from Incyte, completed two Phase 3 trials (STOP-HS1 and STOP-HS2) that met their primary endpoints in March 2025. By week 24, nearly 60% of patients achieved HiSCR50, with 39–51% achieving complete draining tunnel resolution. Regulatory submissions are planned for Europe in 2025 and the US in early 2026. If approved, povorcitinib would become the first oral small-molecule therapy specifically for HS — a potential paradigm shift for patients who prefer non-injectable options.

Sonelokimab, a trivalent nanobody targeting IL-17A, IL-17F, and serum albumin, reported Phase 3 VELA results in September 2025. Using the more stringent HiSCR75 primary endpoint, the combined analysis showed 35.4% versus 21.6% placebo (p<0.001). However, VELA-2 did not meet its composite primary endpoint due to a higher-than-expected placebo response, creating regulatory uncertainty.

Other notable pipeline agents include izokibep (small-protein IL-17A inhibitor; Phase 3 HiSCR50 of 50% vs. 32% placebo), brivekimig (dual TNF/OX40L nanobody; Phase 2a HiSCR50 of 67% vs. 37%), and remibrutinib (BTK inhibitor; Phase 2 HiSCR of 72.7%). Novel targets including the complement pathway and B-cell signaling are being explored, reflecting deepening understanding of HS immunopathology.

The 2024/2025 European S2k guidelines introduced the most significant conceptual shift in HS classification: a two-form system distinguishing active inflammatory disease (graded by IHS4) from predominantly non-inflammatory structural disease (staged by Hurley). This framework directs medical therapy toward inflammation and surgery toward irreversible damage, replacing the previous reliance on Hurley staging alone.

Conclusion

HS and acne vulgaris are distinct diseases that require fundamentally different management strategies. The core distinguishing features for clinicians and patients are the anatomical distribution (intertriginous versus face/trunk), the presence of sinus tracts and chronic drainage (unique to HS), the chronic progressive course without spontaneous resolution, and the failure of standard acne treatments like isotretinoin. For patient education, three points deserve particular emphasis. First, the 7–10 year average diagnostic delay represents a critical problem — earlier recognition prevents irreversible scarring. Second, HS is now treatable with three approved biologics (and an oral JAK inhibitor on the horizon), challenging the historical nihilism around this condition. Third, HS is a systemic inflammatory disease with serious comorbidities requiring holistic, multidisciplinary management, not just skin-level treatment. The 2024–2026 period marks a turning point: HS has evolved from a neglected, single-drug disease to one with a therapeutic landscape approaching the sophistication of psoriasis management.