Hidradenitis suppurativa (HS) flares are triggered when hair follicles in skin folds become blocked, rupture beneath the surface, and set off an intense inflammatory response. But what causes that chain reaction to kick off on any given day involves a mix of hormonal shifts, friction, diet, smoking, body weight, and even the bacteria living on your skin. Understanding these triggers can help you identify patterns and reduce flare frequency.
The Underlying Process Behind Every Flare
Every HS flare starts the same way: a hair follicle gets plugged. The lining of the follicle thickens, trapping dead skin cells and debris inside. Pressure builds until the follicle wall ruptures below the skin’s surface, spilling its contents into the surrounding tissue. Your immune system treats this like a foreign invader, launching an aggressive inflammatory response that produces the painful nodules, abscesses, and draining tunnels characteristic of HS.
This is why HS isn’t an infection or a hygiene problem. It’s a structural failure in the follicle followed by an immune overreaction. Everything on this list of triggers either accelerates follicular plugging, weakens the follicle wall, or amplifies the immune response that follows.
Hormonal Shifts Before Your Period
Among women with HS, 62% report that their disease worsens around menstruation. Of those women, nearly 79% say the flare hits during the week before their period starts, not during it. This timing lines up with the sharp drop in estrogen and progesterone that occurs in the late luteal phase. Women who also experience premenstrual acne breakouts are especially likely to have concurrent HS flares, suggesting a shared hormonal mechanism between the two conditions.
Progesterone-based contraceptives can also be a problem. There are documented cases of HS appearing for the first time after placement of a hormonal IUD containing levonorgestrel, with complete remission after the device was removed. Worsening has also been noted with progesterone-only injections. If you noticed your HS started or got worse after beginning a progesterone-heavy contraceptive, that connection is worth exploring with your provider.
Dietary Triggers: Dairy, Sugar, and Yeast
In a survey of 237 HS patients, roughly half identified dairy products and half identified carbohydrate-rich foods as triggers that worsened their symptoms. The most commonly reported culprits were sweets (68%), bread and pasta (51%), and dairy (51%). These aren’t random associations. Simple carbohydrates and dairy breakdown products like casein and whey raise insulin and a related growth factor called IGF-1, which promotes cell overgrowth in the follicle lining. That overgrowth is what starts the plugging process.
The clinical data backs this up. In one study, 83% of 47 HS patients placed on a dairy-free diet showed clinical improvement. A separate study found that a low-dairy, low-carbohydrate diet led to measurable improvement in disease severity staging among patients who stuck with it.
Brewer’s yeast is a less obvious but well-documented trigger. Found in beer, bread, and some fermented foods, it can provoke flares particularly in people whose immune systems are sensitized to it. In one study, 70% of 37 patients following a yeast-exclusion diet reported symptom improvement, and 87% of them saw lesions return within a week of eating yeast again. That rapid return strongly suggests a direct trigger relationship rather than coincidence.
Smoking and Nicotine
Nicotine directly contributes to follicular plugging through a specific mechanism. The skin around hair follicles in HS patients has a high concentration of receptors that nicotine binds to. When nicotine activates these receptors, it causes excessive growth of the tissue lining the upper part of the follicle, physically narrowing and blocking it. This is the same first step that initiates every flare.
Nicotine also weakens the skin’s defenses by suppressing natural antimicrobial compounds, making follicles more vulnerable to bacterial colonization. On top of that, it stimulates the release of inflammatory signaling molecules while simultaneously impairing the immune cells responsible for resolving inflammation. The result is flares that start more easily and last longer. Quitting smoking is one of the most impactful modifiable factors for HS management.
Body Weight and Skin Friction
A large international study comparing HS patients across BMI categories found that patients with a BMI above 35 had significantly more severe disease than those with a BMI below 25, measured by every metric: clinical staging, number of body areas affected, and patient-reported severity. Even among lower-weight patients, any increase in BMI corresponded to worsening symptoms. Higher body weight increases skin-on-skin contact in the folds where HS occurs, creating more friction, heat, and moisture.
Friction from any source can trigger flares. Tight or form-fitting clothing that rubs against affected areas irritates the skin enough to provoke new lesions. The American Academy of Dermatology specifically recommends loose clothing for HS patients and warns against waxing, which can irritate skin and trigger new sores. Even aggressive scrubbing while washing can cause enough irritation to worsen the disease.
Heat, Sweat, and Humidity
Sweating and overheating are consistent flare triggers. Sweat pools in the skin folds where HS is most active (armpits, groin, under the breasts, inner thighs), creating a warm, moist environment that promotes both follicular occlusion and bacterial growth. Hot weather, intense exercise, and overdressing can all push you past the threshold. This doesn’t mean you should avoid physical activity entirely, but managing how and when you cool down matters. Changing out of sweaty clothes promptly and keeping affected areas dry can reduce flare risk.
Bacterial Imbalance in HS Skin
HS lesions don’t harbor the same bacteria as healthy skin. Normal protective species that keep harmful bacteria in check are significantly reduced in HS-affected areas. In their place, anaerobic bacteria (species that thrive in low-oxygen environments deep in tunnels and follicles) dominate. These include types like Porphyromonas, Prevotella, and Fusobacterium. As disease severity increases, the bacterial community becomes more complex and more dominated by these anaerobes.
This bacterial imbalance activates inflammatory pathways that amplify the immune response already underway from follicular rupture. It’s not that bacteria cause HS, but once the follicle ruptures, the abnormal microbial environment pours fuel on the fire. Larger biofilms with actively growing bacteria have been found in tunnels and deep follicular regions, helping explain why advanced HS is so difficult to bring under control.
Genetic Predisposition
Between 30% and 40% of HS patients report a family history of the disease. A small subset, fewer than 7%, carry identifiable mutations in a protein complex called gamma-secretase, which plays a role in both immune regulation and hair follicle cell development. People with these mutations tend to develop more severe HS at a younger age. But for the vast majority of patients, the genetic contribution is more complex and not traceable to a single gene. Having a family history doesn’t guarantee flares, but it does lower the threshold at which other triggers can set them off.
Stress and the Immune Connection
HS patients consistently have elevated levels of C-reactive protein, a marker of systemic inflammation, compared to people without the condition. This baseline inflammatory state means the immune system is already primed to overreact. Psychological stress, which raises inflammatory signaling throughout the body, can tip that balance toward a flare. While stress is harder to quantify than diet or smoking, many patients identify it as one of their most reliable triggers. The connection likely runs through the same inflammatory pathways that are already dysregulated in HS.