Hurley Stages vs IHS4: What Your HS Severity Score Actually Means

If you live with hidradenitis suppurativa, you may have heard your care described with two different numbers — for example, “Hurley StageHurley Stage: A regional, mainly structural classification system for Acne Inversa in one specific body region, in three stages: Stage I (single abscesses without sinus tracts), Stage II (recurrent abscesses with isolated, still-separated sinus tracts), Stage III (extensive, interconnected sinus tracts and scarring across an entire region). Named after Dr. Helen Hurley. Classic Hurley staging is static and isn't designed to reflect short-term inflammatory activity or response to medical treatment — IHS4 is used alongside it for that.Hurley StageA regional, mainly structural classification system for Acne Inversa in one specific body region, in three stages: Stage I (single abscesses without sinus tracts), Stage II (recurrent abscesses with isolated, still-separated sinus tracts), Stage III (extensive, interconnected sinus tracts and scarring across an entire region). Named after Dr. Helen Hurley. Classic Hurley staging is static and isn't designed to reflect short-term inflammatory activity or response to medical treatment — IHS4 is used alongside it for that.Read more in the glossary II” and “IHS4IHS4 Score: A validated, dynamic tool for measuring current inflammatory disease activity in Acne Inversa (unlike the mainly structural, static Hurley stage). The score is calculated from the number of inflammatory nodules, plus 2 points per abscess, plus 4 points per draining sinus tract; scores up to 3 are mild, 4–10 moderate, 11 or more severe. This allows objective tracking of treatment response over time.IHS4 ScoreA validated, dynamic tool for measuring current inflammatory disease activity in Acne Inversa (unlike the mainly structural, static Hurley stage). The score is calculated from the number of inflammatory nodules, plus 2 points per abscess, plus 4 points per draining sinus tract; scores up to 3 are mild, 4–10 moderate, 11 or more severe. This allows objective tracking of treatment response over time.Read more in the glossary of 7.” These aren’t two ways of saying the same thing. They’re built to answer different questions, and mixing them up is a common source of confusion — including the confusion of thinking a treatment has “done nothing” because a Hurley stage hasn’t moved.

Educational content only. This article explains what Hurley staging and IHS4 each measure, and what changed in 2026 European guidance on using them. It isn’t a self-scoring tool, doesn’t diagnose or stage your HS, and isn’t a substitute for individualized medical advice.

Key takeaways

• Hurley staging mainly describes structural disease — tunnelsSinus Tract: A tunnel-like channel under the skin that forms between abscesses or nodules. Sinus tracts indicate more advanced disease and can chronically drain fluid. They are associated with Hurley Stages II and III.Sinus TractA tunnel-like channel under the skin that forms between abscesses or nodules. Sinus tracts indicate more advanced disease and can chronically drain fluid. They are associated with Hurley Stages II and III.Read more in the glossary, scarring, how confluent the disease is — in one body region, and changes slowly if at all.
• IHS4 is a dynamic score of current inflammatory activity: nodulesNodule: A firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.NoduleA firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.Read more in the glossary, abscessesAbscess: An inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.AbscessAn inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.Read more in the glossary and draining tunnelsDraining Tunnel: A sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Draining TunnelA sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Read more in the glossary, each weighted differently.
• A 2026 update to the European S2k guideline recommends IHS4 and refined Hurley staging for assessing HS, while describing classic Hurley as static and not designed to track how well medical treatment is working.
• Classic Hurley keeps a real role — particularly in planning a surgical approach for a specific region.
• Two body areas can carry different Hurley stages at the same time, because Hurley is regional, not whole-body.
• Pain, drainage, fatigue and quality of life matter enormously and aren’t fully captured by either score.

Why does HS need two different severity systems?

Picture two people. One has several new inflammatory nodules and two abscesses this month, with no established tunnels. The other has extensive old tunnels and scarring in one armpit, but relatively little active inflammation right now. Who has “worse” HS? There’s no single answer until you decide what you’re trying to measure — how much active inflammation is happening now, or how much lasting structural damage has already occurred.

That’s the underlying reason HS assessment increasingly separates active inflammation from structural damage, rather than trying to force both into one scale. The 2025 European S2k treatment guideline already builds its treatment logic around that same split, and the 2026 companion guideline on diagnosis and clinical assessment makes the assessment tools follow the same line: an inflammatory form, tracked with IHS4, and a predominantly structural form, tracked with Hurley staging.

The classic Hurley stages

The Hurley system was introduced in 1989 and remains the best-known way of describing structural HS in a given body region.

Hurley Stage I

One or more abscesses, without tunnels or significant scarring in that region. Lesions can still be painful and recur — Hurley I is about the absence of tunnels and scarring specifically, not about how disruptive the disease feels.

Hurley Stage II

Recurrent abscesses with tunnel formation and scarring, but the affected areas in that region remain separated by patches of unaffected skin.

Hurley Stage III

Diffuse or near-diffuse involvement of the region, or multiple interconnected tunnels and abscesses across it — the most extensive structural pattern.

Does Hurley Stage I mean “mild” HS?

Not exactly, and this is where a lot of patient-facing explanations (including some on this site, until this correction) oversimplify. You’ll often see Hurley I labeled “mild,” Hurley II “moderate,” and Hurley III “severe.” That shorthand isn’t wrong as a rough description of structural extent, but it invites the wrong mental model if it’s read as a complete severity verdict.

Classic Hurley doesn’t count how many inflammatory nodules you have today, how often you flareFlare: A period of acute worsening in a chronic condition. In Acne Inversa, a flare may be triggered by stress, hormonal changes, friction, or other factors and can manifest as new nodules, abscesses, or increased pain.FlareA period of acute worsening in a chronic condition. In Acne Inversa, a flare may be triggered by stress, hormonal changes, friction, or other factors and can manifest as new nodules, abscesses, or increased pain.Read more in the glossary, how much pain you’re in, how much drainage you’re managing, or how HS is affecting your sleep, work or relationships. A person with Hurley I structural disease can still be dealing with frequent, painful flares and a serious impact on daily life. “No tunnels yet in this region” is a more accurate reading of Hurley I than “your HS barely matters.”

Hurley is regional, not a whole-body score

Hurley staging was built to describe a specific anatomical area, not a person’s entire disease at once. In practice, you could have Hurley II in one axilla, Hurley I in the other, and Hurley II again in the groin. When a clinician records “your” Hurley stage as a single number, that’s usually a summary — often the most-affected region — rather than a precise description of every area.

If a Hurley stage is mentioned in a conversation about your care, it’s worth asking which body area it refers to, since the answer for one region may not describe another.

Why doesn’t Hurley staging change much with treatment?

Because it’s built around structural features that don’t disappear quickly, if at all, once they’ve formed. Effective anti-inflammatory treatment can meaningfully reduce new nodules, abscesses and active drainage — real, clinically important improvement. But existing tunnels and scar tissue from before treatment can remain, so the structural pattern in that region may still fit the same Hurley stage.

This is exactly what the 2026 European guideline update means when it describes classic Hurley staging as static: useful for characterizing the structural pattern in a region, but not built to reflect how much inflammation is present within a given stage, and not suited to monitoring whether a medical treatment is working.

What is IHS4?

IHS4 — the International Hidradenitis Suppurativa Severity Score System — was developed specifically to fill that gap: a dynamic measure of current inflammatory activity, validated in a 2017 multicentre study of 236 patients across 11 centres.

It’s calculated from three lesion counts:

IHS4 = number of inflammatory nodules + (2 × number of abscesses) + (4 × number of draining tunnels)

The conventional severity categories are:

• 0–3: mild inflammatory disease activity
• 4–10: moderate inflammatory disease activity
• 11 or more: severe inflammatory disease activity

Why do draining tunnels count more than nodules?

The 1×/2×/4× weighting was derived and statistically validated when IHS4 was developed — it reflects each lesion type’s contribution to the validated score, not a claim that a draining tunnel causes exactly four times more suffering than a nodule. IHS4 is a scoring instrument built for consistency and research use, not a direct measurement of how much a lesion hurts or disrupts your life.

Hurley versus IHS4, side by side

	Classic Hurley	IHS4
Mainly describes	Structural disease (tunnels, scarring)	Current inflammatory activity
Scope	One anatomical region	Lesion counts, generally summed across active areas
Changes with treatment	Slowly, if at all	Can change relatively quickly
Counts nodules and abscesses dynamically	No	Yes
Uses draining tunnels	Yes, structurally	Yes, heavily weighted
Best suited for	Surgical planning for a region	Tracking inflammatory response to treatment

Neither score captures the whole picture on its own — they’re complementary, not competing.

What changed in the 2026 European guideline?

In 2026, an update to the European S2k guideline on HS/acne inversa (Part 1: epidemiology, diagnosis and clinical assessment) recommended IHS4 and refined Hurley staging for assessing HS severity. It kept a place for classic Hurley staging, but a narrower one — chiefly for helping choose a surgical approach for the specific body region being evaluated — while explicitly noting that classic Hurley is static, assesses only individual regions, doesn’t capture how much inflammation is present within a stage, and isn’t a suitable tool for monitoring how well medical treatment is working.

That’s not a claim that Hurley staging is obsolete, and it doesn’t mean every clinician must use IHS4 at every visit. It’s a more precise statement of what each tool is, and isn’t, good for.

What is “refined Hurley” staging?

Recognizing that three broad categories can be too coarse, the Dutch Hidradenitis Suppurativa Expert Group proposed a refined Hurley system that subdivides the traditional stages into more categories, based on factors like the number of body areas involved and the extent of tunnel formation. You don’t need to memorize the subdivisions — the useful takeaway is that HS assessment is moving toward more granularity than a bare Stage I/II/III, not away from Hurley altogether.

Can Hurley change over time?

Structural disease can progress: repeated inflammation in a region can lead to new tunnel formation or increasing scarring, which can shift that region from a lower to a higher Hurley stage. It isn’t, however, a fixed staircase everyone travels — progression isn’t inevitable, and a region can also stay stable for years, especially with sustained treatment of the inflammatory disease driving it.

Hurley III also doesn’t mean nothing can help. It describes extensive existing structural change in a region — it doesn’t mean pain, drainage and quality of life can’t still improve with appropriate treatment, or that procedures addressing the structural disease itself are off the table.

Why doesn’t my score match how I actually feel?

Because neither tool was built to capture everything that matters. Pain, odor, drainage, fatigue, sleep disruption, and the emotional and relationship impact of HS are real parts of the disease burden that a lesion count doesn’t fully translate. A severity score is a useful, standardized way to describe part of your HS — not a replacement for describing how you’re actually doing.

Six questions worth asking at your next appointment

1. Is this Hurley stage describing one body area, or a summary across several?
2. Are we talking mainly about current inflammation, or about structural damage that’s already there?
3. Do you track IHS4, and if so, what’s it been doing over time?
4. What would count as meaningful improvement with this treatment, given that my Hurley stage might not move?
5. If tunnels or scarring are driving a decision in one area, is that different from how we’re managing inflammation elsewhere?
6. Is a Hurley stage feeding into a surgical conversation here, or into a medical-treatment one?

That’s a more productive use of the appointment than trying to work out your own “true” stage beforehand.

How Acne Inversa Life can help

If you want to track current symptoms over time, the Symptom Tracker records pain, drainage and flares as you report them — it doesn’t assign a Hurley stage or IHS4 score. Around a treatment change, a Treatment Checkpoint can compare how things looked before and after, without declaring the treatment a success or failure on your behalf. If tunnels or a possible procedure are on the table, the HS Surgery Planner helps you prepare the structural side of that conversation. And if you’re not sure what a tunnel or scar actually looks like, the visual guide to what HS can look like uses illustrations to build that vocabulary — it’s educational, not a self-staging tool.

The bottom line

“Hurley stage” and “HS severity” aren’t the same thing. Classic Hurley mainly describes structural change — tunnels and scarring — in a specific body region, and it doesn’t move quickly even when treatment is working. IHS4 is a dynamic measure of current inflammatory activity: nodules, abscesses and draining tunnels. A 2026 update to the European guideline now recommends using IHS4 and refined Hurley staging together for assessment, while keeping classic Hurley for what it’s genuinely good at — describing structural disease in a region, including for surgical planning.

Knowing which question a number is answering is what keeps a stable Hurley stage from being misread as “no progress,” and keeps a Hurley stage from being misread as your entire disease.

Choose the next step:

• Understand the basics of HS → What Is Hidradenitis Suppurativa?
• See how tunnels can be assessed beyond a clinical exam → Ultrasound for HS
• Preparing for a procedure → HS Surgery Planner
• See the full range of HS treatments → Treatment Options