What Actually Counts as an HS Flare? The New Consensus Definition Canonical URL: https://www.acneinversa.life/en/blog/hs-flare-definition-guide/ Markdown URL: https://www.acneinversa.life/en/blog/hs-flare-definition-guide.md Plain text URL: https://www.acneinversa.life/en/blog/hs-flare-definition-guide.txt Language: en Category: Flares & Pain Published: 2026-09-12 Last updated: 2026-09-14 Last editorially reviewed: 2026-09-12 Next scheduled review: 2027-09-12 Evidence strength: Moderate evidence — Backed by consistent observational studies or smaller trials. Author: Dr. rer. nat. Dennis Alexander Kwiatkowski (Biochemist, Scientific Writer and Pharma Expert) Scientific editor: Dr. rer. nat. Dennis Alexander Kwiatkowski Reviewer qualifications: Biochemist, Scientific Writer and Pharma Expert Review scope: Scientific literature, clinical guidelines, sources, and editorial clarity Clinical reviewer: No independent clinical review Tags: Acne Inversa, Hidradenitis Suppurativa, HS, Flares & Pain, flare, flare definition, S2k guideline, symptoms, tracking "Flare" is one of the most-used words in daily HS life — and one of the least consistently defined. The new European S2k guideline (Part 1, 2026) sets out a working definition for the first time. What it says, what it deliberately leaves open, and what it means for how you track your own HS. Medical disclaimer: This website is for general educational information only and does not replace medical advice, diagnosis, or treatment. Please speak with qualified medical professionals about symptoms or treatment decisions. 60-second summary - "Flare" gets used constantly in daily HS life, but research has long used it very inconsistently. - The new European guideline (Part 1, 2026) sets out a working definition for the first time: a new or substantial worsening of signs or symptoms. - A flare does not automatically mean permanent worsening, a changed Hurley stage, treatment failure, or infection. - Splitting signs (what you can see) from symptoms (what you feel) helps describe a flare more precisely than just "it's worse". What this means: The definition gives you language for what actually changed — a new lesion, more drainage, more pain — instead of a vague overall impression. What we are less certain about: The guideline sets no fixed threshold (how many days, how much of a pain increase). Where that line sits for you is an individual judgement. What you can do next: Next time you have a flare, note what specifically changed, rather than just that things got "worse". Article You probably know exactly what it feels like when your skin gets worse. Whether that feeling has a precise, shared definition is a different question — and for a surprisingly long time, dermatology did not really have a clear answer. The word "flare" is one of the most commonly used terms in daily HS life — in forums, in appointments, in trackers, on this blog itself. Yet research has used it very inconsistently for years — sometimes meaning a single new lesion, sometimes an entire bad week, sometimes simply "worse than usual." The new European S2k guideline for hidradenitis suppurativa/acne inversa (Part 1, published 2026) dedicates a section to this term for the first time and assigns it a working definition. This article explains what that definition says, what it deliberately leaves open, and what a flare does not automatically mean — because those exact misreadings are often what causes the most worry in daily HS life. For information only. This article explains a working definition drawn from current guideline literature. It cannot establish whether your current symptoms represent a flare, and it does not replace an individual clinical assessment. Key takeaways - "Flare" gets used constantly in daily HS life, but research has long defined it inconsistently. - The new European guideline (Part 1, 2026) sets out a working definition for the first time: a new or substantial worsening of signs or symptoms. - Signs are what's visible or measurable (a new lesion, more drainage); symptoms are what you feel yourself (mainly pain). - A flare does not automatically mean permanent worsening, a changed Hurley stage, treatment failure, or infection. - The guideline sets no fixed threshold (how many days, how much of a pain increase) — that stays an individual judgement. - Knowing what specifically counts as a flare also has practical consequences: some treatment decisions are tied to flare frequency. Why "flare" has been so hard to pin down The problem is not that people with HS don't know when things get worse. The problem is that "worse" can mean many different things: a single new lesion, several at once, more pain without a new lesion, more drainage, or simply an overall worse feeling over several days. In HS research, "flare" (or "exacerbation") has been used differently across different studies for years, often without authors ever stating exactly what they meant by it. That is not a minor detail: when a study reports on "flare frequency" but doesn't say what counted as a flare, its results are hard to compare with other studies — and even harder to apply to any one individual. That inconsistency is a reason the new guideline gives this term its own section at all, rather than continuing to assume everyone already agrees on what it means. What the new working definition says The new guideline describes a flare as a new or substantial worsening of signs or symptoms. Two categories sit inside that one sentence, and the distinction is more useful than it first sounds: Signs — what is visible or measurable: - a new inflammatory lesion (nodule, abscess); - an existing lesion getting worse; - increased drainage or swelling. Symptoms — what you feel yourself, without it necessarily being visible from outside: - pain; - other meaningful worsening of symptoms. Importantly, you don't need both at once. A single new lesion can already meet the definition, just as a substantial increase in pain can, without any new visible change. That lines up fairly closely with what many people with HS already knew from experience — just without a shared word for it until now. What the definition deliberately does not do: it sets no exact threshold — not how many days something needs to last, not how many points pain needs to rise by, not whether one lesion or several are required. That is not an oversight; it reflects how differently HS shows up from person to person. Where the line between "a bit worse" and "a flare" sits in your own case stays an individual judgement — ideally one you work out together with your care team. What a flare does not automatically mean This is exactly where most unnecessary worry comes from, so it is worth stating plainly. A flare does not automatically mean that: - your disease has permanently worsened; - your Hurley stage has changed; - your treatment isn't working; - you caused it yourself; - an infection is present. Each of these deserves a short explanation, because the obvious-seeming conclusion is often the wrong one. No automatic permanent worsening. A flare is, by definition, something new or worsened — it says nothing about whether that state persists. Most flares settle back down. No automatic change in Hurley stage. Hurley staging describes your disease's underlying pattern (isolated abscesses, tunnels with scarring, diffuse involvement) — not the activity on any single day. An acute flare doesn't automatically change that staging. No automatic proof of treatment failure. Individual flares occur even under effective treatment; most therapies reduce overall disease activity without ruling out every single flare. Only a pattern of repeated flares is a good reason to review treatment with your team — not one single episode. No automatic blame. Some flares can be linked to a trigger (heat, friction, your cycle, stress), but many can't. Blaming yourself for it is neither helpful nor supported by the evidence. No automatic sign of infection. HS flares are usually a sterile inflammatory reaction rather than a bacterial infection — even though pain, redness and drainage can resemble infection. Fever, rapidly spreading redness, or feeling significantly unwell are different signals that warrant medical assessment. Why this matters beyond terminology What counts as a flare is not just an academic question — it has real treatment consequences. According to PubMed, a recent expert consensus (a Delphi process from the European Hidradenitis Suppurativa Foundation, 2025/2026) on criteria for earlier first-line biologic therapy explicitly names frequent flares (≥3 in 12 weeks) as one criterion that can support moving to biologic treatment sooner (DOI (https://doi.org/10.1111/jdv.70264)). That shows that even without one single rigid clinical definition, flare frequency is already being used today as a concrete decision factor — one more reason it's worth not just living through flares, but keeping a record you can actually follow. How you can use this for your own tracking The split between signs and symptoms gives you concrete language for next time something changes. Instead of "it's worse," you can note: - Did a new lesion appear, or did an existing one change? - Did drainage or swelling change? - Did pain change — and if so, by how much? - Did other symptoms appear or worsen? That is more useful than a single number on a scale, because it describes what changed, not just that something got worse. The Symptom Tracker (/en/symptom-tracker/) gives you a place to record that as it happens; the companion HS Flare Plan (/en/hs-flare-plan/) helps you note, ahead of time, what has already been agreed with your care team for the next flare. One practical note on how to read this: the Symptom Tracker (/en/symptom-tracker/) records these as two separate things, on purpose. It reports "days with pain ≥5" as a plain quantitative pain metric, and it asks you directly whether a day felt newly or substantially worse — the same working definition described above — rather than guessing at it from your pain score, drainage, or lesion count. The two numbers can differ, and that's expected: a high-pain day is not automatically a flare, and a flare can happen on a low-pain day. What the evidence does not show Current evidence does not show that: - there is one single, universally validated threshold at which something officially counts as a flare; - flare frequency is distributed or predictable in the same way for everyone with HS; - a single flare says anything about the long-term course of your disease; - every flare has an identifiable, nameable cause. The bottom line "Flare" has been one of the most commonly used and least precisely defined words in daily HS life. The new European guideline doesn't fix that with a rigid formula, but with a simple, broadly applicable idea: a new or substantial worsening of signs or symptoms. That's not a checklist to tick off — it's a vocabulary, one that describes what actually changed more precisely than "it's worse" ever could. And that precision is exactly what makes a medical conversation, a tracker entry, or a treatment decision more useful. FAQ Does a flare mean my HS has gotten permanently worse? Not automatically. A flare describes a temporary new or substantial worsening — not necessarily a permanent change to your disease course. Many flares settle back down without the underlying severity having permanently changed. Whether a pattern of repeated flares points to actual progression is a judgement that forms over time and in conversation with your care team, not from a single episode. Does a flare mean my treatment isn't working? Not necessarily. Individual flares can still occur even on effective treatment — most HS therapies reduce overall disease activity without eliminating every single flare. One isolated flare is not proof that treatment has failed. If flares are clearly becoming more frequent, that is a good reason to discuss it with your care team. Does a flare mean there's an infection? Not necessarily. HS flares are usually a sterile inflammatory reaction rather than a bacterial infection, even though pain, redness and drainage can look similar to infection. Signs like fever, rapidly spreading redness, or feeling significantly unwell can point to an actual infection and warrant medical assessment — that's different from a typical flare. Did I cause the flare myself? A flare often cannot be traced to one single cause. Some people notice links to triggers such as heat, friction, their cycle or stress, but many flares happen with no identifiable trigger at all. Blaming yourself for it is neither helpful nor supported by the evidence. Does a single new lesion already count as a flare, or does more need to happen? The new guideline's working definition describes a new or substantial worsening of signs or symptoms — a single new inflammatory lesion can already meet that. The guideline does not set an exact threshold for what counts as "substantial," though. For your own tracking, it is usually more useful to describe concretely what changed than to look for a fixed line. My symptom tracker shows "days with pain 5 or higher." Is that the same as a flare? No, and the tracker doesn't call it one. Pain 5/10 or higher is a plain quantitative pain metric — nothing more. Whether a day counted as a flare is a separate question the tracker asks you directly ("was this newly or substantially worse today?"), based on the guideline's own working definition, and it isn't inferred from your pain score, drainage, or lesion count. You can have a high-pain day that isn't a new flare, and a flare you mark on a day when pain stayed low. References 1. Jemec GBE, Villumsen B, van Straalen KR, et al. European S2k guidelines for hidradenitis suppurativa/acne inversa Part 1. Epidemiology, diagnosis and clinical assessment. - Journal of the European Academy of Dermatology and Venereology, 2026 - https://doi.org/10.1111/jdv.70638 2. Zouboulis CC, Desai N, Emtestam L, et al. European S1 guideline for the treatment of hidradenitis suppurativa/acne inversa. - Journal of the European Academy of Dermatology and Venereology, 2015 - https://doi.org/10.1111/jdv.12966 3. Nikolakis G, Alpsoy E, Anzengruber F, et al. Delphi consensus: First-line use of biologics and small molecules in hidradenitis suppurativa. - Journal of the European Academy of Dermatology and Venereology, 2026 - https://doi.org/10.1111/jdv.70264