Hidradenitis suppurativa is diagnosed clinically using three criteria: the presence of typical lesions, their occurrence in characteristic body locations, and a chronic or recurrent pattern over time.1PubMed. Diagnosing Hidradenitis Suppurativa No blood test or biopsy can confirm the condition on its own, which makes these three pillars the backbone of every diagnosis. Despite the apparent simplicity of the framework, an average of ten years passes between the first symptoms and a correct diagnosis, a gap that carries real consequences for people living with the disease.
The Three Diagnostic Criteria Explained
The three criteria work together as a checklist. All three must be satisfied before a clinician can confidently diagnose HS. Missing even one leaves room for alternative explanations, so understanding what each criterion actually asks for matters.
Typical Lesions
The first criterion asks whether the skin changes look like HS. The hallmark lesions are painful deep-seated nodules, abscesses, and draining sinus tracts (also called tunnels or fistulas).2PubMed. Hidradenitis suppurativa: an update on epidemiology, phenotypes, diagnosis, pathogenesis, comorbidities and quality of life Over time, scarring develops between and around these lesions, sometimes forming rope-like bands under the skin. In early disease, you might only have a single tender nodule that looks deceptively like a boil or an ingrown hair. That resemblance is one reason first episodes are so frequently dismissed.
What distinguishes HS lesions from ordinary boils is the depth and the way they evolve. HS nodules sit deep in the skin and tend to connect to one another via tunnels that burrow through the dermis and subcutaneous fat. When these tunnels drain, the fluid is often foul-smelling, which is distressing but also diagnostically telling. A standard skin abscess usually resolves once drained; HS lesions recur in the same areas and leave progressive scarring behind.
Typical Locations
The second criterion asks where the lesions appear. HS has a strong preference for intertriginous areas, the skin folds where surfaces rub together. The most common sites are the axillae (armpits), the inguinal folds (groin), and the perianal and perineal region.3PubMed Central. Magnetic Resonance Imaging of Hidradenitis Suppurativa: A Focus on the Anoperineal Location The area beneath the breasts (inframammary folds), the buttocks, and the inner thighs are also frequently involved. These regions share a common feature: a high density of apocrine sweat glands and hair follicles, which is relevant because the disease begins with follicular plugging, not with sweat gland infection as was once believed.
Lesions appearing outside these characteristic zones do not automatically rule out HS, but they do raise the diagnostic bar. Some patients develop involvement on the nape of the neck, behind the ears, or on the abdomen, and atypical location patterns may signal a distinct HS phenotype that tends to run a more severe course.
Chronicity and Recurrence
The third criterion is the one most often unmet at the initial visit. To satisfy it, a patient needs to have experienced at least two episodes of lesions within a six-month window. This requirement exists to separate HS from isolated abscesses or one-off infections. In a study of pediatric patients, roughly 43 percent did not meet all three criteria at the time of their first diagnostic visit, and the overwhelming majority of those, about 96 percent, specifically failed the recurrence criterion.4PubMed Central. Evaluation of Hidradenitis Suppurativa Diagnostic Criteria in Pediatric Patients This makes intuitive sense: a patient presenting with their first or second flare simply has not had enough time to demonstrate a pattern of recurrence.
The chronicity requirement protects against overdiagnosis, but it also means that many people with genuine HS are sent away without a diagnosis early on. In practice, experienced dermatologists sometimes make a provisional diagnosis when the lesion type and location are strongly suggestive, then confirm formally once recurrence has been documented. If you have had a painful lump in your armpit or groin that came back after seeming to resolve, that pattern itself is what the third criterion is designed to capture.
Why Diagnosis Takes So Long
The average delay from first symptoms to a formal HS diagnosis is around ten years. During that period, patients typically see more than three different physicians and receive more than three incorrect diagnoses.5PubMed Central. Delayed Diagnosis of Hidradenitis Suppurativa and Its Effect on Patients and Healthcare System The most common misdiagnoses include recurrent boils or folliculitis, simple skin abscesses, infected cysts, and, in the perianal area, pilonidal disease or perianal fistulas from Crohn’s disease.
Several factors feed the delay. General practitioners, who are often the first point of contact, may see only a single lesion during an acute flare and treat it as an isolated abscess. The patient improves temporarily after incision and drainage or a course of antibiotics, and neither the patient nor the doctor connects the dots when the problem returns months later. Embarrassment also plays a role: lesions in the groin, buttocks, and under the breasts are areas many people are reluctant to discuss, and some patients endure years of flares before seeking medical attention.
The lack of a definitive lab test compounds the problem. There is no pathognomonic sign for HS, meaning no single finding that points to the diagnosis beyond question.6Elsevier / Journal of the American Academy of Dermatology. New insights into the diagnosis of hidradenitis suppurativa: Clinical presentations and phenotypes Biopsies can show follicular plugging and inflammation, but those findings are not unique to HS. The diagnosis ultimately rests on a clinician recognizing the pattern across all three criteria, which requires familiarity with the disease.
What Happens Under the Skin
Understanding the basic mechanism helps explain why the diagnostic criteria look the way they do. HS begins in the hair follicle, not in the sweat gland. The earliest detectable changes are thickening and excess keratin buildup in the upper part of the hair follicle, which eventually plugs it. The blocked follicle swells, and the surrounding tissue becomes inflamed. Eventually the follicle wall ruptures, dumping its contents, including keratin, bacteria, and hair fragments, into the surrounding dermis.7British Journal of Dermatology. Aetiology and pathogenesis of hidradenitis suppurativa The immune system reacts aggressively, forming abscesses and, over repeated cycles, sinus tracts lined with epithelium that never fully heal.
This cycle of plugging, rupture, inflammation, and tunneling explains why HS recurs in the same areas and why it favors skin folds rich in hair follicles. It also explains why the three diagnostic criteria focus on lesion type, location, and recurrence: the disease is defined by a self-perpetuating loop that plays out in specific anatomical zones over and over again.
How Severity Is Measured After Diagnosis
Once HS is diagnosed, clinicians grade its severity. The most widely used framework is the Hurley staging system, which divides patients into three stages based on the extent of disease:
- Stage I: One or more isolated abscesses without sinus tracts or scarring.
- Stage II: Recurrent abscesses with sinus tracts and scarring, but separated by stretches of normal skin.
- Stage III: Diffuse or near-diffuse involvement of an entire region, with multiple interconnected sinus tracts and abscesses and no remaining normal skin between them.
Hurley staging is static, meaning it captures the worst state a particular area has reached but does not track changes over time.8PubMed Central. Hidradenitis suppurativa – known and unknown disease A patient in Hurley stage II who improves dramatically on treatment is still classified as stage II. That limitation led to the development of the International Hidradenitis Suppurativa Severity Score System (IHS4), a dynamic tool that counts individual lesions. Each nodule counts as one point, each abscess as two, and each draining tunnel as four. A total of three or less is mild, four to ten is moderate, and eleven or higher is severe.9PubMed. Development and validation of the International Hidradenitis Suppurativa Severity Score System (IHS4), a novel dynamic scoring system to assess HS severity The IHS4 responds to treatment changes, making it more useful for tracking disease over time or comparing outcomes in clinical trials.
Neither staging system is itself a diagnostic tool. They enter the picture only after HS has been confirmed, guiding treatment decisions and helping clinicians communicate severity to patients and insurers.
When Ultrasound Adds to the Picture
HS is a clinical diagnosis, but imaging, particularly high-frequency Doppler ultrasound, is increasingly used to detect disease that cannot be seen or felt on examination. Ultrasound can reveal dilated hair follicles, dermal pseudocysts, fluid collections with debris, and fistulous tracts running below the skin surface. A scoring framework called the SOS-HS has been proposed: if three or more of these characteristic ultrasound findings are present, the diagnosis of HS is supported sonographically.10PubMed Central. Doppler ultrasound protocol for patients with hidradenitis suppurativa More recently, experts have validated the identification of “hair tracts,” fragments of hair with a distinctive layered appearance on ultrasound, as another diagnostically useful marker.
The real value of ultrasound lies in what it reveals that clinical examination misses. A patient who appears to have Hurley stage I disease on the surface may have subclinical tunnels or collections that change the severity assessment entirely. For surgeons planning excision, knowing the full extent of tunneling beneath the skin can mean the difference between adequate and inadequate margins. Ultrasound is not required for diagnosis, but at centers with expertise it is becoming a routine part of the workup.
Family History and Genetic Risk
A clinician taking a history for suspected HS will often ask about family members with similar symptoms. Roughly 30 to 40 percent of patients report a family history of the disease, and twin studies suggest that the heritability of HS is high, around 77 percent in one large cohort analysis.11PubMed Central. Genetic factors associated with hidradenitis suppurativa, a literature review Several families carry mutations in genes encoding components of the gamma-secretase complex, a group of enzymes involved in Notch signaling, a pathway critical to normal hair follicle development. These mutations follow an autosomal dominant inheritance pattern with incomplete penetrance, meaning you can carry the mutation without developing the disease.12PubMed. Hidradenitis Suppurativa: Comprehensive Review of Predisposing Genetic Mutations and Changes
That said, the genetics of HS are not reducible to a single gene. Three distinct forms have been proposed based on genetic architecture: sporadic (no clear family link), familial (inherited gamma-secretase mutations), and syndromic (HS appearing alongside other autoinflammatory or keratinization disorders).13PubMed Central. Hidradenitis Suppurativa: A Perspective on Genetic Factors Involved in the Disease Most patients fall into the sporadic category, where multiple genes, environmental triggers, and immune factors interact in ways that are still being mapped out. Family history strengthens a diagnostic suspicion but is far from necessary. The majority of people with HS have no affected relatives that they know of.
Conditions That Travel With HS
Clinicians diagnosing HS should also screen for associated metabolic conditions. People with HS are significantly more likely to have metabolic syndrome, diabetes, obesity, and hypertension compared to the general population. One large dataset found that HS visits had roughly three times the odds of accompanying obesity and hypertension and nearly twice the odds of hyperlipidemia.14PLoS One. Chronic companions: An updated national cross-sectional study of metabolic syndrome comorbidities in outpatient visits for hidradenitis suppurativa Earlier hospital-based studies reported even stronger associations, with odds ratios for diabetes and general obesity several times higher in HS patients than in matched controls.15PubMed. Association of metabolic syndrome and hidradenitis suppurativa
Whether obesity contributes to causing HS, worsens it mechanically through friction and occlusion, or simply shares underlying inflammatory drivers is still debated. In practice, the relationship means that an HS diagnosis should prompt a broader metabolic check, including blood pressure, fasting glucose, and a lipid panel. Addressing these comorbidities does not cure HS, but uncontrolled metabolic disease can make flares worse and complicate treatment with biologics or surgery.
Atypical Phenotypes and Why They Matter
Not everyone with HS fits the textbook picture of armpit and groin lesions. Research using statistical modeling of clinical data from hundreds of patients has identified at least three HS subtypes. The largest group, called the axillary-mammary type, resembles classic HS affecting flexural skin. Two other subtypes, a follicular type and a gluteal type, are considered atypical and tend to involve more severe disease. These atypical phenotypes are more common in men.16Oxford Academic. Leveraging genotypes and phenotypes to implement precision medicine in hidradenitis suppurativa management
The follicular subtype often presents with prominent comedones (blackheads), papules, and pustules alongside the deeper nodules and tunnels, which can lead to confusion with severe acne or dissecting cellulitis of the scalp. The gluteal subtype can be mistaken for pilonidal disease or perianal Crohn’s. Recognizing that HS has multiple faces is clinically important because atypical presentations tend to progress to more advanced disease if left undiagnosed, and they may respond differently to treatment. If you have recurrent painful lesions in less classic locations but also have some involvement in a typical site, that combination should still raise the question of HS.
The Diagnostic Challenge in Children and Adolescents
HS was once considered an adult disease, but it can start in adolescence and occasionally even earlier. Diagnosing HS in younger patients is especially tricky because the recurrence criterion is harder to satisfy. A teenager presenting with a first painful groin nodule at fourteen may not meet all three criteria for years, during which time the disease can progress silently. As noted in the pediatric study above, nearly all of the children who failed to meet diagnostic criteria at the initial visit were tripped up by the recurrence requirement.4PubMed Central. Evaluation of Hidradenitis Suppurativa Diagnostic Criteria in Pediatric Patients
Puberty-related hormonal changes appear to play a role in triggering onset, since HS rarely appears before the apocrine glands become active. Clinicians evaluating a young patient with a suspicious lesion in a characteristic location should document it carefully and schedule follow-up rather than dismissing it as a one-time event. Early treatment, even before formal criteria are fully met, can limit scarring and tunneling that would otherwise become permanent.
What You Can Do to Speed Up Diagnosis
If you suspect you might have HS, a few practical steps can help shorten the diagnostic timeline. Keep a record of every flare: when it started, where on the body, how long it lasted, and whether it drained. Photographs are especially useful because lesions may have partially resolved by the time you see a doctor. This documentation can satisfy the recurrence criterion even if flares do not happen to coincide with your appointments.
Ask to see a dermatologist rather than relying solely on a general practitioner, especially if you have had repeated “boils” in the armpits, groin, or under the breasts that keep coming back. Mention any family members who have dealt with similar recurring skin problems. And if a clinician diagnoses you with recurrent abscesses but cannot explain why they keep returning in the same body areas, push for a second opinion. A ten-year diagnostic delay is not inevitable, but narrowing that gap requires both patient awareness and clinician familiarity with a disease that remains underrecognized in primary care.