Hidradenitis suppurativa (HS) starts when a hair follicle becomes blocked, usually in a skin fold like the armpit or groin. The first thing you’ll typically notice is a painful, deep lump that looks like a pimple or boil. Most people develop their first symptoms in their late teens, though a smaller group first experiences HS in their mid-40s.
What Happens Inside the Skin
HS begins with a problem in the hair follicle. Skin cells that normally shed and clear away instead build up inside the follicle, plugging it. This blockage causes the follicle to swell with trapped material, including dead skin cells (keratin) and bacteria. As pressure builds, the follicle eventually ruptures beneath the skin’s surface.
When the follicle breaks open, its contents spill into the surrounding tissue. Your immune system treats this like an invasion, flooding the area with inflammatory cells. That immune response is what creates the painful, swollen lump you feel. In HS, the immune reaction tends to be more intense than it should be, driven partly by a malfunction in the body’s innate immune defenses. This is why HS is now considered an auto-inflammatory condition rather than simply an infection or an acne-like problem.
If this cycle repeats in the same area, the inflammation can destroy the original hair follicle and damage nearby structures, eventually forming tunnels beneath the skin that connect separate lesions. But in its earliest stage, HS presents as isolated lumps without tunnels or scarring.
What the First Symptoms Feel and Look Like
Before a visible lump appears, many people notice warning signs in the area: swelling, a burning sensation, itching, or excessive sweating. These sensations can precede the lump by hours or days.
The first actual sign is a deep, painful spot that looks like a large pimple, acne cyst, or boil. These nodules are typically 0.5 to 2 centimeters across and sit deep in the skin rather than near the surface. They can persist for days to months. The most common locations for a first lesion are the armpits, groin, buttocks, and inner thighs, all areas where skin rubs against skin.
Early on, these breakouts often clear up on their own, which can give the false impression that the problem has resolved. But HS is defined by recurrence. New lumps tend to return in the same area, sometimes in the exact same spot. This pattern of clearing and returning is one of the key features that distinguishes HS from a one-time boil or skin infection.
Why It Gets Mistaken for Something Else
HS diagnosis is delayed by an average of 7 to 10 years from the first symptoms. One large study of 285 patients found a mean delay of just over 10 years, and that number hasn’t improved much over time. The main reason is that early HS looks almost identical to common skin abscesses or cellulitis, and many clinicians who aren’t specialists in the condition don’t think to consider it.
Because each individual lump can look like an ordinary boil, many people go through cycles of being treated for skin infections before anyone recognizes the pattern. Doctors diagnose HS by looking at three things together: the type of lesion (deep nodules), the location (skin folds), and the fact that it keeps coming back. If you’ve had recurring painful lumps in your armpits, groin, or inner thighs, that combination is the hallmark of HS, even if each episode was previously treated as a simple abscess.
Hormones and the Timing of Onset
HS almost always starts around puberty, which strongly suggests that sex hormones play a role in triggering the disease. The most common onset occurs in the mid-teen years, accounting for about 79% of cases. A smaller second wave, roughly 21% of cases, begins in the mid-40s.
For women with HS, hormonal fluctuations have a clear effect on flares. Studies have found that 43% to 77% of women with HS report worsening symptoms around their menstrual period. The disease also tends to flare after pregnancy. These patterns point to a relationship between hormone shifts and the follicular blockage that kicks off each new lesion, though the exact mechanism isn’t fully mapped out.
Genetics and Family History
HS has a strong hereditary component. Between 30% and 42% of people with HS report a family member with the same condition, and a twin study estimated the heritability of HS at 77%. A small subset of patients carry mutations in genes that code for a protein complex involved in cell signaling. When this signaling pathway malfunctions, hair follicles convert into keratin-filled cysts and the skin’s immune surveillance becomes chronically overactive.
Most HS cases, roughly 60% to 70%, aren’t driven by a single gene mutation but instead appear to result from the combined effect of many genetic variants, each contributing a small amount of risk. This is why HS can run in families without following a clean inheritance pattern. You might have a parent with mild disease and develop a more severe form, or vice versa.
Smoking and Other Contributing Factors
Smoking is one of the most well-established modifiable risk factors for HS. Nicotine interacts with receptors found in the cells that line the upper portion of hair follicles, promoting the kind of overgrowth that leads to follicular plugging. It can also alter the skin’s bacterial environment in ways that may sustain chronic inflammation. Quitting smoking doesn’t guarantee improvement, but it removes one of the forces actively driving the disease process.
Obesity is the other major risk factor. Excess weight increases friction in skin folds and promotes a low-grade inflammatory state throughout the body. Mechanical friction alone doesn’t cause HS, but in someone who already has the underlying predisposition, it can determine where and how severely lesions develop. Weight loss has been shown to reduce flare frequency and severity in some patients, particularly those with disease concentrated in areas of skin-on-skin contact.
Earliest Stage HS
Clinicians classify HS severity using a three-tier system. The earliest stage, Hurley Stage I, is defined as one or more abscesses without any tunnels connecting them and without scarring. At this point, the disease is considered uncomplicated, and treatment typically starts with topical approaches. Many people live at this stage for years or even indefinitely, never progressing further.
Progression isn’t inevitable, but it’s more likely when early HS goes unrecognized and untreated. Repeated inflammation in the same area gradually damages tissue and can create the scar tissue and tunnels that define more advanced stages. This is one reason the long diagnostic delay matters so much: the earlier you recognize the pattern and begin managing it, the better your chances of keeping the disease from advancing.