Hidradenitis suppurativa (HS) is diagnosed clinically, meaning a doctor can identify it based on what the lesions look like, where they appear, and how often they come back. No blood test, biopsy, or imaging scan is required. Despite this, the average person with HS waits 7 to 10 years between first symptoms and a formal diagnosis, largely because the condition is frequently mistaken for ordinary boils or skin infections.
The Three Criteria Doctors Look For
A diagnosis of HS rests on three elements that a doctor evaluates together during a physical exam.
The first is the type of skin changes present. HS produces deep-seated, painful nodules and abscesses that sit well below the skin’s surface. In more advanced cases, tunnels form under the skin connecting separate lesions, and distinctive scarring patterns develop, including double-ended blackheads and thick, rope-like scars.
The second is location. HS lesions cluster in areas where skin folds rub together: the armpits, groin, buttocks, breasts, and sometimes the abdominal fold or inner thighs. A painful lump on the forearm, for instance, is unlikely to be HS. The pattern of where bumps appear is one of the strongest diagnostic clues.
The third is recurrence over time. A single abscess in the armpit isn’t enough. Doctors look for at least two lesions within a six-month period, typically recurring at or near previous sites. This chronic, relapsing pattern is what separates HS from a one-time skin infection.
Why It Takes So Long to Get Diagnosed
HS is commonly confused with several other conditions. Folliculitis (inflamed hair follicles), ordinary boils, severe acne, inflamed cysts, and even a skin manifestation of Crohn’s disease can all look similar early on. Many people see their first HS lesion and assume it’s an infected ingrown hair or a boil that will resolve on its own. When it does come back, they may visit an urgent care clinic or primary care doctor who treats each flare-up as a standalone infection rather than recognizing the recurring pattern.
This piecemeal approach is a major reason the diagnostic delay averages 7 to 10 years. Each visit may result in antibiotics or a drainage procedure, but nobody connects the dots across multiple episodes. By the time a dermatologist sees the patient, the disease may have progressed significantly.
No Biopsy or Lab Test Is Needed
HS is a clinical diagnosis. A skin biopsy is not required to confirm it. Doctors may occasionally order a biopsy, bacterial culture, or imaging if they need to rule out other conditions that mimic HS, but these tests exist to eliminate alternatives rather than to confirm HS itself. If your doctor can see the characteristic lesions in the right locations and you report a history of recurrence, that’s typically sufficient.
Skin ultrasound is sometimes used, particularly in specialized dermatology clinics, to reveal what’s happening beneath the surface. High-frequency ultrasound can detect tunnels, fluid collections, and inflammation that aren’t visible on the skin. This is most useful when a doctor suspects the disease is more extensive than it appears or needs to plan a surgical approach, not as a first-line diagnostic tool.
How Doctors Assess Severity
Once HS is diagnosed, your doctor will evaluate how severe it is. The most common framework is the Hurley staging system, which groups the disease into three stages. Stage I involves individual abscesses without connecting tunnels or significant scarring. Stage II means abscesses recur more widely, with some tunnels forming between lesions. Stage III describes large areas of skin with interconnected abscesses and sinus tracts across an entire region.
A more precise scoring method, the IHS4 (International Hidradenitis Suppurativa Severity Score System), assigns points based on a count of active lesions: one point per nodule, two points per abscess, and four points per draining tunnel. A total score of 3 or less is mild, 4 to 10 is moderate, and 11 or higher is severe. This score helps track whether the disease is improving or worsening over time, especially during treatment.
Staging matters because it shapes what treatments your doctor recommends. Mild disease might be managed with topical or oral therapies, while severe disease often requires biologic medications or surgery.
What to Bring to Your Appointment
Because recurrence is one of the three diagnostic criteria, the history you share with your doctor is just as important as what they can see on the day of your visit. If your skin is between flares and looks relatively clear, the diagnosis can be harder to make on the spot. Keeping a record of past flare-ups helps considerably.
Before your appointment, note when and where previous lumps appeared, how long each one lasted, whether they drained on their own, and whether new ones showed up in the same area. Photos taken during active flares are especially valuable. If you’ve been treated for “boils” or “abscesses” multiple times in the past, mention that directly, even if it was years ago and at a different clinic. That pattern of recurrence is often the missing piece that leads to a correct diagnosis.