Hidradenitis suppurativa (HS) is diagnosed through a physical exam and your medical history. There is no blood test, imaging scan, or biopsy required for a standard diagnosis. A dermatologist looks for three things: characteristic lesions (deep nodules, abscesses, or tunnels under the skin), location in specific body areas, and a pattern of recurrence over time. If all three are present, that’s enough for a diagnosis. Despite this seemingly straightforward process, most people wait an average of 7 to 10 years before getting the correct answer.
The Three Criteria Doctors Look For
An HS diagnosis rests entirely on what a doctor can see and what you can tell them about your history. The three required criteria are:
- Typical lesions. Deep, painful nodules (usually 0.5 to 2 cm), abscesses that may drain fluid, tunnels connecting under the skin, and scarring. Unlike ordinary boils, HS nodules sit deep beneath the surface, recur in the same spots, and can form interconnected channels that drain or ulcerate.
- Characteristic locations. HS develops in areas where skin folds and rubs together. The armpits are the most common site. Other frequent locations include the groin, inner thighs, under the breasts, the buttocks, and the perianal and genital areas.
- Chronic or recurrent course. A single episode isn’t HS. The pattern that clinches the diagnosis is lesions that come back over months or years, often with periods of partial improvement in between. Onset typically begins between puberty and young adulthood.
If your doctor can confirm all three, the diagnosis is made on the spot. No lab work is needed to confirm it.
Why It Takes So Long to Get Diagnosed
Despite clear diagnostic criteria, the average delay from first symptoms to a correct HS diagnosis is about 10 years. A 2024 study of 285 patients found the mean delay was 10.1 years, and this number has not improved over time.
Several factors drive this gap. Early HS can look like ordinary boils, ingrown hairs, acne, or recurring skin infections. Many people treat flare-ups at home or visit urgent care for what seems like a one-off abscess. Doctors who aren’t dermatologists may not recognize the pattern, especially in early stages when scarring and tunnels haven’t yet developed. Because the lesions appear in intimate areas, some people delay seeking care altogether.
If you’ve been dealing with painful, recurring lumps in your armpits, groin, or other skin-fold areas for months, bringing up the full history of your flare-ups (not just the current one) can help a doctor connect the dots faster.
What Happens During the Exam
A dermatologist will visually inspect the areas where HS commonly appears and feel for nodules or tunnels beneath the skin. They’ll ask how long you’ve been having flare-ups, how often they recur, and whether they drain on their own. They’ll also look for scarring from previous episodes, which is a strong indicator of ongoing disease.
In more advanced cases, you may notice open pores that look like blackheads clustered together. These are sometimes called “tombstone” comedones and are a hallmark of later-stage HS. Thick, rope-like scars and skin that feels firm or distorted in affected areas also point toward a longer disease history.
Family history matters too. About 35% of people with HS have a family member with the condition. Researchers have identified mutations in specific genes involved in skin cell signaling in some families, though genetic testing isn’t part of a routine diagnosis. Your doctor may simply ask whether anyone in your family has dealt with similar recurring skin problems.
When Imaging or Biopsy Is Used
Most people don’t need any testing beyond a clinical exam, but there are situations where additional tools help. High-frequency ultrasound is increasingly used in specialized HS clinics because it can detect tunnels and fluid collections beneath the skin that aren’t visible or palpable during a standard exam. These subclinical lesions can change how severe your disease actually is compared to what it looks like on the surface. Ultrasound is also useful for mapping the extent of disease before surgery and for tracking how well treatment is working over time.
A skin biopsy is not routine for HS, but a doctor may recommend one if there’s concern about another condition. Long-standing, severe HS carries a small risk of squamous cell carcinoma developing in chronically scarred or draining areas, so any unusual changes in a long-term lesion may warrant a biopsy to rule that out.
How Severity Is Classified
Once diagnosed, your doctor will assess how severe your HS is using the Hurley staging system, which groups the disease into three stages based on what’s happening in your skin:
- Stage I: One or more abscesses, but no tunnels or scarring. This is the earliest and most common presentation.
- Stage II: Recurring abscesses with some tunnel formation and scarring. Lesions may be single or multiple but are still separated from each other.
- Stage III: Widespread involvement with multiple interconnected tunnels and abscesses covering large areas, leaving little unaffected skin in the region.
Hurley staging gives a snapshot of where your disease stands, but it wasn’t designed to track changes over time. For monitoring treatment response, doctors may use scoring tools that count the number of active nodules, abscesses, and draining tunnels at each visit. One widely used measure, called HiSCR, defines a meaningful treatment response as at least a 50% reduction in the total count of nodules and abscesses with no new abscesses or draining tunnels. These tools help your care team decide whether a treatment plan is working or needs to be adjusted.
Conditions HS Gets Confused With
Part of the reason diagnosis takes so long is that early HS mimics several common skin problems. Ordinary boils (furuncles) caused by bacterial infection look similar but tend to be isolated events rather than recurring in the same body regions. Severe acne on the body, infected hair follicles, pilonidal cysts near the tailbone, and Crohn’s disease (which can cause perianal abscesses and fistulas) are all conditions that get confused with HS.
The key distinction is the combination of location, recurrence, and lesion type. A single abscess in the groin isn’t HS. But if you’ve had three or more painful episodes in skin-fold areas over the course of six months or longer, especially if some have left scars or connected under the skin, the pattern strongly suggests HS and warrants evaluation by a dermatologist familiar with the condition.