New Study Finds Hidden Scalp Inflammation That May Help Explain Why Dissecting Cellulitis Returns and Spreads

Paired scalp biopsies found PIILIF in all 12 normal-looking scalp samples and all three quiet nodules, while active lesions showed added pus-forming inflammation and tissue damage on a PIILIF background

MANHATTAN BEACH, Calif., Aug. 4, 2026 /PRNewswire/ -- Researchers at Dr. U Hair and Skin Clinic in the Los Angeles area report that dissecting cellulitis of the scalp may affect more than the painful bumps, drainage and tunnels visible on the surface. Their open-access, peer-reviewed paper, "Perifollicular Lymphocytic Inflammation and Fibrosis in Dissecting Cellulitis: Evidence of a Consistent Histopathologic Pattern," was published July 17 in Clinical, Cosmetic and Investigational Dermatology.

Dissecting cellulitis is a chronic scalp disease that can cause painful lumps, pus, tunnels beneath the skin and permanent scarring hair loss. The study examined PIILIF, a hidden pattern of immune inflammation and early scarring around the upper hair follicle. PIILIF was found in active lesions, quiet nodules and scalp that looked normal.

"Dissecting cellulitis is usually recognized after it becomes painful, drains pus or forms tunnels," said Sanusi Umar, MD, board-certified dermatologist and lead author. "Our findings suggest these visible flares may sit on top of a quieter, wider inflammatory process involving normal-looking scalp. That changes where we look, when we biopsy and what future treatment studies need to address."

Study design and key findings

Researchers reviewed 12 consecutive men with dissecting cellulitis confirmed clinically and by biopsy. High-magnification scalp imaging guided paired biopsies from normal-looking scalp and either an active lesion or a quiet nodule. Two blinded, board-certified dermatopathologists independently reviewed the samples.

Key findings included:

• PIILIF was found in all 12 normal-looking scalp biopsies and all three quiet nodules.
• All nine active lesions showed the pus-forming inflammation and tissue damage typical of dissecting cellulitis superimposed on PIILIF.
• Three patients had previously been treated for presumed seborrheic dermatitis, or dandruff, but none of the study biopsies supported that diagnosis. This raises the possibility that subtle PIILIF-related changes may sometimes be mistaken for dandruff.

Why the findings matter

The presence of PIILIF across normal-looking scalp, quiet nodules and active lesions suggests it may be a broader underlying component of dissecting cellulitis rather than a finding limited to visible flares. This may help explain why the condition returns after a flare appears quiet, spreads into nearby scalp or overlaps with other scarring hair-loss conditions.

The paper builds on earlier PIILIF studies from Dr. Umar's group in acne keloidalis nuchae and androgenetic alopecia, suggesting a recurring follicle-centered pattern across different forms of hair loss.

"The recurring pattern raises the possibility that PIILIF is a foundational inflammatory component shared across several difficult hair-loss conditions," Umar said. "That remains a hypothesis, but it creates a focused research path: determining whether addressing PIILIF alongside active inflammation improves long-term control."

The authors caution that this was a small, retrospective study, and larger controlled studies are needed to determine whether PIILIF predicts new lesions, recurrence, progression or treatment response.

About Dr. Sanusi Umar

Sanusi Umar, MD, is a board-certified dermatologist, founder of Dr. U Hair and Skin Clinic, and a UCLA and Harbor-UCLA clinical instructor specializing in complex hair loss and scarring alopecias.

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