Three overlapping layers, genetics, immune dysregulation, and environmental triggers, drive HS rather than a single cause. Hidradenitis suppurativa is a chronic inflammatory skin disease driven by a hair follicle that plugs and ruptures, an immune system that overreacts to that rupture, and a genetic blueprint that loads everything up in the first place. Smoking, hormones, friction, and body weight act as the HS triggers that light the match. The disease has nothing to do with poor hygiene.
Below, we walk through how a plugged follicle, an overreactive immune response, and inherited DNA all stack together to spark HS, then map the smoking, hormone, friction, and weight factors that keep fueling it.
Follicular Occlusion Is the First Physical Event in HS
The starting event in HS happens deep inside a hair follicle, far beneath the skin surface where a pimple or boil seems to sit. Keratin, the same protein that makes up hair and the outer skin layer, builds up inside the follicle alongside sebum and shed skin cells. That mixture forms a plug, the follicle swells, and pressure builds until the wall finally gives way.
When the wall ruptures, everything trapped inside spills into the surrounding dermis, and the immune system reacts as if the body is under attack.
That rupture is the moment the disease actually begins. The early lesion looks and feels like a deep, painful nodule in the armpit, groin, under the breasts, or along the buttocks. Because of the location, HS is often misdiagnosed for years as recurring boils, staph infections, or stubborn acne. Doctors may prescribe repeated courses of antibiotics or perform incision and drainage without ever naming the underlying problem.
HS is sometimes called “inverse acne” or “acne inversa” because the pattern looks like acne but lives in skin folds where acne does not normally appear.
The Follicle, Not the Sweat Gland, Starts Everything
Older theories blamed apocrine sweat glands, which is why the condition was historically named after them. Modern pathology has shown the sweat glands are innocent bystanders. The apocrine ducts empty into the same follicles that plug up, so they become involved only after the follicle has already ruptured. The follicle is the starting structure, and everything else downstream, including tunneling tracts and scarring, is a consequence of that initial breakdown.
Because the trigger is mechanical plugging rather than bacterial invasion, antiseptic washes and short antibiotic courses rarely change the long-term course. Major dermatology bodies describe HS as a follicular occlusion disease, which puts it in the same family as certain forms of acne and pilonidal disease. Treating it like an infection misses the root cause, and that mismatch is part of why so many people cycle through providers before getting a real answer.
The Genetic Architecture Behind HS and Familial Inheritance
The second layer of what causes HS sits in your DNA. Family clustering is one of the strongest clues: roughly 30 to 40 percent of people with HS have at least one affected relative, and having a first-degree relative with HS raises your own risk about threefold compared with the general population. Identical twin studies show much higher concordance than fraternal twins, which points to inherited variation rather than shared household exposure alone.
Gamma-Secretase Mutations Drive the Familial Form
The clearest genetic signal in HS involves the gamma-secretase complex, a group of proteins that helps cells communicate and shed properly. Mutations in NCSTN (which encodes nicastrin), PSEN1, and PSENEN disrupt this complex and account for most familial HS cases. When gamma-secretase does not work correctly, the follicle’s normal turnover breaks down, and keratin and debris pile up faster than the skin can clear them. The result is a genetic predisposition to follicular plugging that runs through families.
Variants in another gene, PSTPIP1, link HS to a family of related inflammatory syndromes, including PASH (pyoderma gangrenosum, acne, and HS) and PAPASH (pyoderma gangrenosum, acne, pyogenic arthritis, and HS). These conditions involve the same follicular occlusion mechanism plus an exaggerated inflammatory response. They are rare, but they help explain why HS sometimes travels with other immune-driven skin and joint problems in the same person or the same family.
Polygenic Risk in the More Common, Non-Familial Form
Most people with HS do not have a single dramatic gene mutation. Instead, they inherit many small variations across dozens of genes that, together, tilt follicular biology and immune regulation toward disease. This is called polygenic risk, and it follows the same pattern seen in psoriasis, type 2 diabetes, and many other chronic conditions. Genetic predisposition loads the gun, but the trigger almost always comes from somewhere else.
That split helps explain why HS can show up in adulthood, skip a generation, or appear in someone with no obvious family history at all.
| Gene or Region | Role in HS | Inheritance Pattern |
|---|---|---|
| NCSTN (nicastrin) | Gamma-secretase subunit; impaired follicular shedding | Autosomal dominant, familial HS |
| PSEN1, PSENEN | Other gamma-secretase subunits; same mechanism | Autosomal dominant, familial HS |
| PSTPIP1 | Links HS to PASH and PAPASH syndromes | Autosomal dominant, syndromic HS |
| Polygenic background | Many small variants affecting immunity and skin | Non-Mendelian, common HS |
Immune Dysregulation and the Cytokines Driving HS Inflammation
Once a follicle ruptures, the chronic inflammation that defines HS gets going. The immune cells that respond release signaling proteins called cytokines, and in HS, several of those cytokines stay elevated far longer than they should. Tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1), and interleukin-17 (IL-17) are consistently high in HS lesions, along with IL-12 and IL-23.
This is why HS is now classified as an immune-mediated inflammatory disease, much closer to psoriasis or inflammatory bowel disease than to a simple skin infection.
These cytokines recruit more immune cells, keep the area inflamed, and help form the tunnels and abscesses that mark moderate to severe HS. The tunnels, called sinus tracts, are not just scars. They are active, inflamed channels lined with immune cells that continue to release cytokines even between visible flares. That persistence is part of why HS often feels like it never fully goes away.
Why the Auto-Inflammatory Label Matters
HS is sometimes described as auto-inflammatory rather than autoimmune. In autoimmune disease, the immune system attacks a specific target, like thyroid tissue or joint linings. In auto-inflammatory disease, the immune system overreacts to internal triggers, like debris from a ruptured follicle, without a specific target. HS fits the auto-inflammatory pattern, which is why a doctor focusing on antibodies may not find a clear autoimmune marker, yet inflammation still rages.
This immune signature is also why dermatologists now use targeted therapies that block specific cytokines. Recognizing HS as a real inflammatory disease, with measurable drivers, helps separate it from older stigma. The condition is not caused by being unclean or noncompliant. It is driven by a verifiable immune cascade.
Smoking, Obesity, and Other Modifiable Risk Factors
The single strongest modifiable risk factor for HS is smoking. Roughly 70 to 90 percent of people with HS smoke or have a significant smoking history, and current smokers tend to develop HS earlier, in more locations, and with more severe lesions than non-smokers. Nicotine alters follicular keratinization, promotes inflammation, and impairs wound healing, which together amplify every other risk factor in the disease.
Quitting smoking does not cure HS, but it consistently improves severity over time and may help treatments work better.
Obesity is the second major modifiable factor. Adipose tissue, especially around the abdomen and thighs, increases skin-on-skin friction, traps heat and moisture in body folds, and releases its own inflammatory cytokines. A higher body mass index (BMI) correlates with earlier HS onset and greater lesion burden. Weight loss of even 5 to 10 percent can reduce new lesion formation in many people, though deep tunnels and scarring will not reverse on their own.
Everyday Mechanical and Environmental Aggravators
Beyond smoking and weight, several smaller factors consistently worsen HS:
- Tight clothing digs into the groin, waistband, or under breasts and increases pressure on already vulnerable follicles.
- Shaving or waxing affected areas can micro-tear follicles and trigger new lesions, so many dermatologists recommend stopping both.
- Heat and humidity increase sweating and skin fold moisture, which worsens follicular plugging.
- Prolonged sitting creates sustained pressure on the buttocks and upper thighs, a common HS site.
- Heavy exercise sweating without a prompt shower can leave residue that fuels occlusion in skin folds.
- Stress and sleep deprivation raise cortisol and other inflammatory signals that precede flares in many patients.
Multi-site HS registries track exactly these variables, and their data show that people who address smoking, weight, and friction together tend to need fewer medical interventions than those who change only one. None of these factors cause HS on their own. They lower the threshold at which the underlying genetic and immune tendencies express themselves.
Hormonal Shifts, Friction, and Environmental Triggers of Flares
Hormones are among the most consistent HS triggers, especially for women. Androgens, the hormones often associated with testosterone but present in all sexes at varying levels, stimulate sebum production and shift keratin behavior inside the follicle. HS typically appears after puberty, flares around menstrual cycles, often worsens in the weeks before a period, may intensify during pregnancy, and frequently shifts with perimenopause. Many people report improvement after menopause, while others see persistent activity if inflammation has already tunneled into place.
Birth control pills, anti-androgen medications, and pregnancy itself all change the hormonal backdrop. None of these changes cause HS in someone who would not otherwise develop it, but they shape when symptoms emerge and how severely they progress. Tracking flares against the menstrual cycle on a calendar or app often reveals a pattern that was not obvious at first.
Friction, Sweat, and Climate as Daily Triggers
Mechanical friction is a quiet but powerful trigger. Seams from underwear or jeans rubbing against the inner thigh, waistbands pressing into the lower abdomen, or a seatbelt edge cutting across the shoulder all create repeated micro-trauma on follicles that are already prone to plugging. Repetitive motion at work, whether from lifting, cycling, or running, compounds that pressure.
Hot and humid environments make everything worse. Sweat softens the outer layer of the skin, salt crystals irritate follicles, and moisture trapped in folds encourages bacterial overgrowth that further inflames the area. Many people moving from a dry climate to a humid one notice a sudden uptick in flares. Stress-related cortisol surges sit in the same category: they do not cause HS, but they reliably precede new lesions in people who are already predisposed.
What Can and Cannot Be Changed, A Practical Framework for Reducing Risk
Sorting HS risk into modifiable and non-modifiable buckets makes the disease feel less like a random punishment and more like a manageable equation. Non-modifiable factors include family history, the sex you were assigned at birth (HS is more common in women, especially after puberty), age of onset, and the specific gene variants you carry. None of these change with effort, and blaming yourself for them is medically inaccurate.
Modifiable factors include smoking, body weight, clothing choices, sweat and friction management, stress reduction, and shaving habits. These are the levers you can actually pull, and they sit alongside medical care, not in place of it. Long-term control of HS almost always depends on pairing medical treatment with consistent trigger reduction, because neither alone reliably controls moderate disease.
A Practical First Step
A useful first move is requesting a dermatologist referral, ideally one familiar with HS, and bringing two pieces of information to that appointment. First, a written family history, including any relatives with chronic abscesses, severe acne, pilonidal disease, or related inflammatory conditions. Second, a personal trigger diary covering at least four to six weeks of food, menstrual cycle, clothing, activity, and flare notes.
Warning: avoid spending months trying to identify a single food trigger. Diet matters for general inflammation, but HS is primarily a follicular and immune disease. Starving yourself of broad food groups usually does more harm than good and rarely changes lesion counts on its own.
From there, a stepwise plan usually beats a sweeping overhaul. Stop smoking, or cut back meaningfully, before attempting other major changes. Address weight loss after smoking is addressed, since nicotine withdrawal already stresses the body. Choose breathable, loose-fitting clothing, especially around known lesion sites. Replace razors with electric clippers or skip hair removal in affected areas entirely. Shower promptly after sweating, and pat (don’t rub) skin folds dry.
These small, consistent moves lower the daily inflammatory load and create room for medical treatment to work.
The Bottom Line
HS starts with a hair follicle that plugs and ruptures, gets amplified by an immune system running too hot, and gets pulled into active disease by genetic predisposition plus smoking, weight, hormones, friction, and stress. You inherit the wiring; you can still change the volume. Treating the disease well means treating all three layers at once, with a dermatologist who knows HS and a daily routine that respects what your skin is actually up against.
FAQ
Is HS genetic?
Yes, partially. Familial HS exists, especially with mutations in NCSTN, PSEN1, and PSENEN, and a first-degree relative with HS raises your risk about threefold. Most cases, however, involve many small inherited variants rather than a single dramatic gene, which is why HS can appear without any obvious family history.
What triggers an HS flare?
Hormonal shifts around menstrual cycles, friction from tight clothing, heat and heavy sweating, emotional stress, poor sleep, and shaving or waxing affected areas top the list of common flare triggers. Smoking and higher body weight raise the background risk and make flares more frequent.
Does smoking cause hidradenitis suppurativa?
Roughly 70–90% of people with HS have a smoking history, making cigarettes the strongest modifiable risk factor even though they do not directly cause the disease. Up to 70 to 90 percent of people with HS smoke, and smoking is linked to earlier onset, more widespread lesions, and greater severity. Quitting improves outcomes even after the disease has started.
Can hormones cause HS?
Androgens do not act alone, but they strongly shape when HS symptoms first appear and how the disease behaves over time. HS usually starts after puberty, often flares before menstruation, and frequently changes with pregnancy and perimenopause. Anti-androgen treatments help some patients, especially women with cycle-linked flares.
What genes are linked to HS?
The clearest links are NCSTN, PSEN1, and PSENEN, which encode parts of the gamma-secretase complex and drive familial HS. PSTPIP1 connects HS to PASH and PAPASH syndromes. Most non-familial HS involves many smaller genetic variants affecting follicular biology and immune regulation together.
Is HS an autoimmune disease?
Researchers classify HS as an immune-mediated inflammatory disease, placing it more precisely within the auto-inflammatory category rather than classical autoimmunity. The immune system overreacts to internal triggers like ruptured follicular contents rather than attacking a specific tissue target. This is why HS often travels with other inflammatory conditions and responds to drugs that block cytokines like TNF-alpha and IL-1.
