Introduction
Hidradenitis suppurativa, often abbreviated HS, is identified primarily through clinical evaluation rather than a single confirmatory laboratory test. It is a chronic inflammatory skin disease that affects areas where skin rubs together, especially the armpits, groin, buttocks, inner thighs, and under the breasts. The condition develops when hair follicles become blocked and inflamed, leading to deep, painful nodules, recurrent abscesses, drainage, and over time, scar formation and tunnel-like tracts under the skin. Because these changes can resemble boils, infections, or other dermatologic disorders, accurate diagnosis matters. A correct diagnosis helps avoid repeated ineffective treatment, prevents unnecessary procedures, and allows earlier management of inflammation, pain, and long-term scarring.
Recognizing Possible Signs of the Condition
The first clue to hidradenitis suppurativa is usually the pattern of lesions rather than any single skin finding. Doctors suspect the condition when a patient reports recurrent painful lumps in the same body areas, especially in regions with apocrine-bearing and friction-prone skin folds. These lumps may enlarge into abscesses, break open, and drain blood-tinged or purulent fluid. The lesions tend to come back after seeming to heal, which distinguishes HS from a one-time skin infection.
Other signs include blackheads that appear in pairs or clusters, thickened skin, persistent tenderness, and the development of sinus tracts, which are narrow channels under the skin that connect inflamed pockets. Over time, repeated inflammation can leave rope-like scars or bridged scar tissue. In some people, the disease is mild and presents mainly as intermittent nodules. In more advanced cases, there may be multiple interconnected tracts and extensive scarring. The distribution and recurrence of the lesions are key to recognizing HS as a follicular inflammatory disorder rather than a simple abscess problem.
Medical History and Physical Examination
Diagnosis begins with a detailed history. Clinicians ask when the lesions first appeared, how often they recur, where they occur, and whether they have progressively worsened. They also ask about drainage, odor, pain, fever, and prior treatment with antibiotics, incision and drainage, or other therapies. A history of repeated lesions in characteristic areas strongly raises suspicion for HS.
Medical professionals also explore factors that may support the diagnosis or influence severity. These include smoking, obesity, family history, menstrual flare patterns, androgen-related symptoms, and associated inflammatory or metabolic conditions. HS has a known tendency to cluster in families, which can suggest a genetic predisposition affecting follicular keratinization and innate immune signaling. Doctors may also ask about how the skin disease affects daily functioning, since chronic pain and drainage often lead to delayed diagnosis.
The physical examination focuses on lesion morphology and location. Clinicians look for deep-seated nodules, fluctuant abscesses, open or draining sinuses, double-headed comedones, and scarring. They assess whether lesions are in classic intertriginous sites and whether there are signs of chronicity, such as tunnels or fibrotic plaques. The examiner may map the involved areas to determine disease extent and stage. Because HS is an inflammatory follicular disease, the exam often reveals a combination of active lesions and older structural skin changes at the same time.
Diagnostic Tests Used for Hidradenitis suppurativa
There is no single blood test that confirms hidradenitis suppurativa. In most cases, diagnosis is clinical, meaning it is made from the history and physical examination. Testing is used selectively to exclude other conditions, evaluate complications, or assess severe disease.
Laboratory tests may be ordered when infection is suspected or when the presentation is atypical. A complete blood count can show signs of systemic inflammation or infection, although it is not specific for HS. In patients with draining lesions, bacterial culture of exudate may be done if secondary infection is a concern, especially when fever, cellulitis, or treatment failure is present. However, a positive culture does not establish HS; it only identifies organisms that may be complicating an already inflamed lesion. Some clinicians may also order tests related to associated conditions, such as glucose or hemoglobin A1c when insulin resistance or diabetes is suspected, or inflammatory markers in select cases, but these are supportive rather than diagnostic.
Imaging tests are useful when deeper disease is suspected. Ultrasound is increasingly used because it can reveal tunnels, fluid collections, and subclinical inflammation that may not be obvious on the skin surface. It can help define the extent of interconnected tracts and assist in planning procedures. In more complicated cases, magnetic resonance imaging may be ordered, especially for involvement of the perineal, gluteal, or anogenital region, where disease may extend deeper than expected. MRI can show the architecture of sinus tracts, abscesses, and surrounding tissue inflammation. Plain X-rays are not typically used to diagnose HS, but may be helpful if bone involvement or another process is being considered.
Functional tests are not commonly part of the diagnosis itself, but evaluation of function and impact can be clinically important. Physicians may assess range of motion if lesions are near the groin or axillae, because pain and scarring can limit movement. They may also document severity scores or activity measures to track disease burden over time. These tools do not confirm HS, but they help clinicians determine how extensive the inflammatory process is and whether the condition is affecting daily physical function.
Tissue examination is reserved for uncertain cases or when another diagnosis must be excluded. A skin biopsy is not usually required in classic HS and may be non-specific if performed on a typical lesion. When done, histopathology may show follicular occlusion, rupture of the follicular unit, mixed inflammatory infiltrates, fibrosis, and sinus tract formation. The main value of biopsy is often to rule out cancers, granulomatous diseases, or other inflammatory disorders, rather than to prove HS directly. In long-standing, severe disease, biopsy may also be used to evaluate for rare malignant transformation in chronically scarred areas.
Interpreting Diagnostic Results
Doctors interpret the findings by looking for a characteristic combination: recurrent lesions, typical body sites, and chronic inflammatory changes such as abscesses, tunnels, and scarring. If these features are present, the diagnosis is usually HS even if laboratory tests are normal. This is because HS is driven by follicular occlusion and a dysregulated inflammatory response, not by a single detectable pathogen or marker.
Results from cultures, blood tests, or imaging are considered in context. For example, a positive bacterial culture may indicate secondary infection but does not negate HS. An ultrasound showing subcutaneous tunnels or multiple connected abscesses can strengthen the diagnosis, especially when physical findings are subtle. Conversely, if imaging or biopsy reveals features more consistent with another disease, the clinician may reconsider HS. In practice, diagnosis depends on pattern recognition and exclusion of mimics, not on any one test result.
Severity is often interpreted using the Hurley staging system. Stage I involves isolated nodules or abscesses without tunnels or extensive scarring. Stage II includes recurrent lesions with limited sinus tract formation and scarring. Stage III represents diffuse involvement with multiple interconnected tracts and widespread scarring. Staging does not establish the diagnosis by itself, but it helps clinicians describe disease burden and guide management.
Conditions That May Need to Be Distinguished
Several disorders can resemble hidradenitis suppurativa, particularly early in the course. Recurrent furuncles or carbuncles caused by bacterial infection can look similar, but these often occur as isolated infectious events rather than a chronic pattern in typical HS locations. Epidermoid cysts may become inflamed and drain, yet they usually present as discrete cystic lesions with a central punctum rather than recurrent interconnected disease.
Folliculitis can also cause bumps in hair-bearing areas, but it is generally more superficial and less likely to produce deep scarring or sinus tracts. Crohn disease with perianal involvement may resemble HS in the groin or buttocks, and the two conditions can occasionally coexist. Lymphogranuloma venereum, tuberculosis, actinomycosis, and other chronic infections may enter the differential when lesions are persistent or draining, particularly in genital or perineal regions. Pilonidal disease can cause draining sinuses near the sacrococcygeal area, but its location and anatomy usually differ from classic HS.
Noninfectious conditions also matter in the differential diagnosis. Cutaneous Crohn disease, pyoderma gangrenosum, acne conglobata, and dissecting cellulitis of the scalp are part of the follicular occlusion spectrum and may overlap with HS. Doctors distinguish these by lesion distribution, associated systemic findings, biopsy results when needed, and the presence of hallmark HS features such as recurrent nodules, tunnels, and scarring in intertriginous sites.
Factors That Influence Diagnosis
Several factors can make diagnosis easier or more difficult. Disease stage is one of the most important. Early HS may present only as intermittent painful nodules, without tunnels or obvious scarring, making it easy to mistake for boils or ingrown hairs. In advanced disease, the diagnosis is often more apparent because of chronic sinus tracts and fibrotic scarring.
Age can also influence recognition. HS most commonly begins after puberty and often appears in young adulthood, which can lead clinicians to think first about acne or infection. Pediatric cases are less common and may prompt a broader search for alternative explanations. Older patients may have atypical presentations or longstanding undiagnosed disease that is mistaken for recurrent abscesses.
Body habitus, smoking status, and hormone-related factors do not diagnose HS, but they can shape clinical suspicion because they are associated with disease risk and flare patterns. Coexisting conditions such as obesity, diabetes, inflammatory bowel disease, metabolic syndrome, and polycystic ovary syndrome may also affect the evaluation. In some patients, diagnostic uncertainty persists because lesions are intermittently active and the skin appears nearly normal between flares. That is one reason medical history is so important: the disease may be evident in the story even when the exam is quiet.
Conclusion
Hidradenitis suppurativa is diagnosed through careful clinical assessment supported, when needed, by targeted tests. Doctors look for a recurring pattern of painful nodules, abscesses, drainage, tunnels, and scarring in characteristic body areas, then use history and physical examination to determine whether the presentation fits a chronic follicular inflammatory disorder. Laboratory studies, imaging, and biopsy are used selectively to rule out infection, define extent, or exclude other diseases. Because HS has no single definitive blood test, accurate diagnosis depends on recognizing its specific pattern of recurrent inflammation and structural skin change. When medical evaluation combines those observations with appropriate testing, clinicians can identify HS reliably and distinguish it from similar conditions.