Hidradenitis suppurativa (HS) typically starts with a single, painful, pea-sized lump under the skin that persists for weeks or months, usually in an area where skin rubs together like the armpits or groin. What sets it apart from an ordinary boil is that it comes back, often in the same spot, and may eventually leave scars or form tunnels beneath the skin. If that pattern sounds familiar, there’s a good chance HS is worth investigating, but the condition is notoriously underdiagnosed: the average person waits about 10 years and sees more than three different doctors before getting a correct diagnosis.
The Three Signs Doctors Look For
A clinical diagnosis of HS is based on three criteria, and all three need to be present. First, the lesions look a certain way: deep, painful nodules or abscesses under the skin, not surface-level pimples. Second, they show up in specific locations, the skin folds where friction and moisture are highest. Third, and most importantly, they recur. The working threshold most specialists use is two or more flare-ups in the same general area within six months.
If you’ve had a single boil once in your armpit that healed and never came back, that’s probably not HS. If you keep getting painful lumps in your groin every few weeks, or your armpits have developed hard, rope-like scars from repeated flare-ups, the pattern fits.
What HS Lumps Feel and Look Like
The earliest lesions are firm, tender bumps deep under the skin. They’re not like a regular pimple sitting on the surface. They feel more like a marble or pea buried beneath the skin, and they hurt, sometimes intensely, even before anything is visible. These nodules can persist for weeks before they either slowly shrink or rupture and drain blood and pus.
As the condition progresses, you may notice other signs. Blackheads that appear in pairs (called double-ended comedones) are a hallmark of HS and rarely show up in ordinary acne. The skin in affected areas can develop rope-like scars or become pitted. In more advanced stages, tunnels called sinus tracts form beneath the skin, connecting separate lumps. These tracts can ooze a mucus-like or bloody fluid and heal extremely slowly, if at all.
Where HS Shows Up on the Body
HS has a strong preference for intertriginous areas, the places where skin folds press against each other. The most common locations are the armpits and groin. Beyond those two, lesions frequently appear in the buttocks and perianal area, under the breasts, around the genitals, and along the inner thighs. Less commonly, they can show up behind the ears, on the scalp, on the back, or on the mons pubis.
Location is one of the clearest clues separating HS from other conditions. Regular acne favors the face, chest, and upper back. Folliculitis (infected hair follicles) can appear almost anywhere but tends to be shallow and clears with basic treatment. HS concentrates in skin folds and produces deeper, more persistent lumps that leave lasting changes in the skin.
How HS Differs From Boils and Acne
A one-off boil and an early HS nodule can look almost identical, which is a big reason the condition gets misdiagnosed so often. The differences become clear over time. Ordinary boils are usually caused by a bacterial infection in a single hair follicle. They come to a head, drain, and heal within a couple of weeks. HS nodules sit deeper, last longer, and keep coming back in the same regions.
Other distinguishing features include the paired blackheads mentioned above, the development of sinus tracts connecting separate lumps, and scarring that thickens or pits the skin. If you’ve been treated repeatedly for “boils” or “ingrown hairs” with antibiotics and the problem keeps returning in the same area, that recurrence pattern is itself a red flag for HS.
Who Is Most Likely to Develop HS
Most people notice their first symptoms before age 30, often during late adolescence or their early twenties. A smaller group develops symptoms for the first time in their mid-40s. HS is roughly three times more common in women than men, and studies show higher rates among Black patients compared to white patients, though it affects people of all races.
Smoking and higher body weight are the two most consistently identified modifiable risk factors. HS also shows up alongside a cluster of related conditions: metabolic syndrome, type 2 diabetes, inflammatory bowel disease (especially Crohn’s disease), and certain forms of inflammatory arthritis. Having one of these conditions doesn’t mean you have HS, but if you’re dealing with recurring painful lumps and you also have one of these diagnoses, it strengthens the case for bringing HS up with a dermatologist.
The Stages of HS
Doctors use the Hurley staging system to describe how far the disease has progressed. It has three levels:
- Stage I: One or more abscesses, but no sinus tracts or significant scarring. This is where most people are when they first start wondering what’s going on. The lumps come and go, and the skin between flares may look relatively normal.
- Stage II: Recurrent abscesses with one or more sinus tracts and scarring, separated by areas of normal skin. At this point the disease is clearly chronic, and you can often feel cord-like tracks beneath the surface.
- Stage III: Multiple interconnected sinus tracts and abscesses covering broad areas with little or no normal skin in between. This is the most severe stage and typically involves significant pain and drainage.
Most people searching for answers are likely in stage I or early stage II. The value of recognizing HS early is that treatment can help slow progression and reduce scarring before sinus tracts become established.
Why It Takes So Long to Get Diagnosed
One large study found the average delay from first symptoms to a correct HS diagnosis was 10 years. During that time, patients saw an average of more than three different doctors, including general practitioners, surgeons, and gynecologists, and received more than three incorrect diagnoses along the way. Common misdiagnoses include simple skin infections, folliculitis, ordinary boils, and sexually transmitted infections (when lesions occur in the groin or genital area).
Part of the delay is that mild HS genuinely does look like other, more common conditions in its early stages. Another part is that many primary care providers receive limited training on HS and may not think to ask about recurrence patterns or check for scarring in skin fold areas. If you suspect HS, asking specifically about the condition by name and describing the full history of your flare-ups, including how often they recur and exactly where, gives a provider the information needed to make the connection.
What to Track Before Your Appointment
If you’re planning to bring this up with a doctor, keeping a brief record of your symptoms helps. Note where each lump appears, how long it lasts, whether it drains on its own, and how often new ones develop. Photograph active flare-ups if you can, since lesions may be quiet at the time of your visit. A dermatologist is the specialist most equipped to diagnose HS, but many general practitioners can make the diagnosis too if given a clear picture of the pattern.
The key details that point toward HS over other conditions: lumps that recur at least twice within six months, location in skin fold areas, and any scarring or tunneling between lesions. If your experience matches that profile, you have a strong basis for pursuing a formal evaluation.