Why Dissecting Cellulitis Keeps Coming Back: Hidden Inflammation Beyond the Visible Scalp Bumps

A new study finds PIILIF in normal-looking scalp and clinically quiet nodules, offering new clues to relapse, spread and permanent scarring hair loss.

If your scalp bumps settle and then return, read this

A painful scalp bump appears. Pressure builds. It may become tender, swell, drain pus and then seem to calm down.

For a while, there is relief.

Then the same area becomes active again, or a new bump appears nearby.

For people living with dissecting cellulitis, this cycle can affect far more than the scalp. Drainage can stain pillowcases, hats or clothing. There may be concern about odor. Haircuts become difficult. Pain interferes with sleep. Visible scarring and hair loss can cause embarrassment and make people withdraw socially.

The most frustrating part is often the recurrence. A bump can look quiet while the disease later returns in that area or extends elsewhere.

Our newly published study asked whether the visible bumps are only part of the story.

The answer may be important: in this small study, a hidden pattern of inflammation and early fibrosis called PIILIF was found not only in active dissecting cellulitis lesions, but also in every normal-looking scalp sample and every clinically quiet nodule examined. 

What is dissecting cellulitis of the scalp?

Dissecting cellulitis of the scalp, also called perifolliculitis capitis abscedens et suffodiens, is a chronic, relapsing form of scarring alopecia.

It can cause:

• Deep, painful scalp bumps 
• Pus-filled lesions 
• Drainage 
• Abscesses 
• Tunnels beneath the skin, also called sinus tracts 
• Thickened scar tissue 
• Permanent hair loss 

As the condition becomes more destructive, hair follicles can rupture and be replaced by scar tissue. Once a follicle has been permanently destroyed by scarring, it may no longer be capable of producing hair. 

Dissecting cellulitis has traditionally been understood mainly through its most visible and destructive phase: inflamed nodules, pus, follicular rupture, tunnels and scarring.

But those features do not fully explain why the disease returns after appearing quiet, why it spreads into nearby scalp or why a firm residual bump can later become inflamed again.

The question our study asked

We asked a straightforward question:

In a patient with dissecting cellulitis, is scalp that looks normal truly normal under the microscope?

The study included 12 consecutive men with dissecting cellulitis confirmed through clinical examination and biopsy.

Using magnified scalp examination, called trichoscopy, we obtained two small scalp samples during the same evaluation:

1. One biopsy from scalp that showed no visible nodule, pustule, tunnel or hair loss 
2. One biopsy from an active lesion or, when no active lesion was present, a firm but clinically quiet nodule 

The specimens were examined in both vertical and horizontal planes and independently reviewed by two board-certified dermatopathologists who were blinded to the clinical details. 

What we found beneath normal-looking scalp

PIILIF was found in all 12 normal-looking scalp biopsies.

PIILIF stands for perifollicular infundibulo-isthmic lymphocytic inflammation and fibrosis. In plain language, it describes immune-cell inflammation and early fibrotic change concentrated around the upper part of the hair follicle.

This means that scalp without visible bumps, pus, tunnels or hair loss still showed a consistent inflammatory and early fibrotic pattern under the microscope.

That finding supports the possibility that dissecting cellulitis may affect a wider field of scalp than the visible lesions suggest. 

The qualification matters: this was a small, specialty-clinic cohort. Finding PIILIF in 12 of 12 normal-looking samples does not establish that it is present in every person with dissecting cellulitis.

A quiet bump may not be biologically quiet

Three patients had no visibly active lesion when their biopsies were taken. Instead, they had firm residual nodules without redness, tenderness, drainage or other signs of active inflammation.

PIILIF was found in all three clinically quiet nodules.

These quiet nodules did not show the destructive, pus-forming changes seen in active disease. Their sebaceous glands, commonly known as oil glands, were also preserved.

This is an important distinction.

A nodule that looks calm may no longer be in an active destructive phase, but the presence of PIILIF suggests that the tissue may not be completely normal at the microscopic level. Because only three quiet nodules were studied, this finding should be viewed as an early clue that requires confirmation in larger studies. 

What changes when dissecting cellulitis becomes actively destructive

The nine active lesions showed two overlapping patterns.

The first was PIILIF, the upper-follicle inflammatory and early fibrotic pattern also found in normal-looking scalp.

The second was the aggressive, pus-forming destruction traditionally associated with active dissecting cellulitis.

Among the nine active lesions:

• All nine contained neutrophils, the white blood cells strongly associated with pus-forming inflammation 
• Five showed granulation tissue, indicating ongoing injury and tissue repair 
• Six showed complete loss of sebaceous glands 
• Six showed follicular rupture or destruction 
• Six contained hair shafts released into the surrounding tissue 

In other words, active disease did not replace PIILIF. The destructive flare appeared on top of a PIILIF background. 

The oil-gland clue

Sebaceous glands are part of the hair-follicle unit and produce the oils associated with the follicular environment.

In the study:

• Sebaceous glands were preserved in the clinically quiet nodules 
• Complete sebaceous gland loss was absent from the matched normal-looking scalp samples 
• Complete sebaceous gland loss was found in six of the nine active lesions 

This difference raises an important possibility: sebaceous gland destruction may help mark a transition toward a more damaging and potentially less reversible phase of disease.

That is a hypothesis, not a proven sequence.

Because the study examined patients at one point in time, it could not determine whether PIILIF develops first, whether it persists after an active lesion improves or whether quiet nodules represent partly treated lesions, spontaneously improved lesions or samples taken outside a destructive focus. 

Why dissecting cellulitis may relapse or spread

The findings support what researchers call a field-effect hypothesis.

Under this model, the painful, draining bumps are the most visible expression of the disease, but a quieter inflammatory field may extend into scalp that appears unaffected.

This could help explain:

• Why a flare returns after appearing to settle 
• Why new lesions develop near previously affected areas 
• Why a quiet nodule later becomes active 
• Why visible treatment of one bump may not address the full scalp environment 
• Why dissecting cellulitis sometimes overlaps with other follicle-centered scarring disorders 

The study shows an association across these scalp states. It does not yet prove that PIILIF causes relapse, predicts spread or inevitably progresses into a destructive lesion. 

Why “dandruff” can be misleading

Three of the 12 patients had previously been treated for presumed seborrheic dermatitis, commonly called dandruff.

None of the biopsies taken for this study showed the microscopic features needed to support seborrheic dermatitis.

This does not mean that ordinary dandruff is dissecting cellulitis. Seborrheic dermatitis is common, and most people with dandruff do not have PIILIF or dissecting cellulitis.

The practical message is narrower:

When redness, scale or flaking persists alongside painful bumps, drainage, progressive scarring or unexplained hair loss, the diagnosis may deserve another look.

The study authors also acknowledged that prior antifungal shampoos or topical corticosteroids could have reduced signs of seborrheic dermatitis before biopsy. The absence of seborrheic dermatitis in these samples therefore cannot prove that every earlier diagnosis was wrong. 

How this connects with acne keloidalis nuchae and the wider PIILIF research

Three of the 12 patients, or 25%, also had biopsy-confirmed acne keloidalis nuchae (AKN) on the back of the scalp. PIILIF was also identified in a sideburn biopsy from one patient. 

These findings connect with two earlier studies from our group.

In our AKN study, PIILIF was found in normal-looking scalp in all 41 patients examined. That work proposed that a broader, clinically subtle follicle-centered process may coexist with visible AKN lesions. 

In our androgenetic alopecia study, PIILIF was found in normal-looking scalp in 81% of a 129-patient referral-center cohort and was more common in advanced or treatment-resistant pattern hair loss. 

Taken together, these studies identify a recurring upper-follicle inflammatory and early fibrotic pattern across clinically different forms of hair loss.

They do not yet prove that PIILIF is the universal cause of AKN, pattern baldness, dissecting cellulitis or every scarring alopecia. They do, however, establish a focused research direction that deserves further study.

What this study does not prove

The findings are important, but they must be interpreted within the study’s limits:

• The cohort included only 12 men from one specialty clinic 
• There was no healthy control group 
• Only three clinically quiet nodules were studied 
• The study was retrospective and cross-sectional 
• It cannot establish whether PIILIF comes before, follows or persists after active disease 
• Prior treatments were not standardized and may have changed some biopsy findings 
• The study did not compare treatments 
• It did not prove that treating PIILIF prevents relapse, spread or permanent hair loss 

Larger controlled studies following patients over time are needed to determine whether PIILIF predicts new lesions, extension, relapse or treatment response. 

What patients should do

Consider evaluation by a dermatologist experienced in scarring alopecia when you have:

• Recurrent painful scalp bumps 
• Pus or repeated drainage 
• Firm nodules that repeatedly become inflamed 
• Tunnels beneath the scalp 
• Progressive scarring or permanent hair loss 
• Disease extending beyond the original lesion 
• Persistent redness or scale that does not behave like routine dandruff 
• A history of dissecting cellulitis together with AKN, severe acne or hidradenitis suppurativa 

Not every patient needs multiple biopsies. The decision should be based on the history, clinical examination, palpation, trichoscopy, prior pathology and the question that needs to be answered.

The central lesson from this research is simple:

Do not assume that the edge of the visible bump is necessarily the edge of the disease.

Request a Complex Dissecting Cellulitis and Scarring Alopecia Evaluation

For patients with recurrent, extensive, treatment-resistant or diagnostically unclear scalp disease, a focused evaluation can help define the diagnosis, disease extent and next clinical steps.

Frequently Asked Questions

Is PIILIF the same as dissecting cellulitis?

No. Dissecting cellulitis is the clinical disease that produces painful nodules, pus, tunnels, scarring and permanent hair loss. PIILIF is a microscopic pattern of upper-follicle inflammation and early fibrosis that may represent a quieter component of the disease.

Does this study mean the entire scalp is diseased?

No. The study found PIILIF in all 12 selected normal-looking biopsy sites, but the cohort was small and the sites were chosen with trichoscopy. The findings support a possible wider inflammatory field, not a conclusion that every follicle or every area of scalp is equally affected.

Does a quiet nodule mean the disease is cured?

Not necessarily. In this small study, all three clinically quiet nodules still contained PIILIF, although they lacked the destructive pus-forming features of active lesions. More research is needed to understand what quiet nodules represent over time.

Does dandruff mean I have PIILIF or dissecting cellulitis?

No. Dandruff is common and usually unrelated to dissecting cellulitis. Further evaluation becomes more relevant when scale or redness occurs with recurrent painful bumps, drainage, scarring, tunnels or progressive hair loss.

Did this study identify the best treatment for dissecting cellulitis?

No. The study evaluated biopsy findings, not treatment effectiveness. It provides a framework for future studies testing whether care should address both visible destructive flares and the quieter PIILIF component.

Do I need a biopsy?

Not everyone does. A biopsy may be useful when the diagnosis is uncertain, disease continues to recur, the visible findings do not explain the symptoms or a clinician needs to determine what is happening beyond the active lesion.

Publication

Perifollicular Lymphocytic Inflammation and Fibrosis in Dissecting Cellulitis: Evidence of a Consistent Histopathologic Pattern

Published in Clinical, Cosmetic and Investigational Dermatology on July 17, 2026. 

Medical note: This article is for educational purposes and does not provide medical advice. Diagnosis and treatment must be individualized by a qualified clinician. The study discussed here did not compare treatments.