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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Dermatology · Folliculitis Decalvans

The Path to Diagnosis: Tests and Comparisons

At a Glance

Folliculitis decalvans is diagnosed by combining a scalp examination with magnified scalp viewing, and sometimes a bacterial culture or punch biopsy. Doctors compare the findings with conditions such as lichen planopilaris to confirm the diagnosis and guide individualized care.

Confirming a diagnosis of folliculitis decalvans (FD) is a detective process. Because FD can look like other types of permanent hair loss, your dermatologist will individualize your evaluation, using a combination of tools to see both what is happening on the surface and what is occurring deep beneath the skin [1][2].

The Diagnostic Toolkit

A complete evaluation for FD may involve several steps, though not every patient requires all of them:

  1. Clinical Exam: Your doctor looks for the “signature” signs of FD, such as pustules, crusting, and redness, particularly on the crown or back of the head [3].
  2. Trichoscopy: Using a handheld magnifier called a dermatoscope, the doctor examines your scalp at high power. In FD, they are looking for tufted hairs (multiple hairs from one opening), yellow tubular scales, and red dots that signal active inflammation [3][4].
  3. Microbiological Culture: Your doctor may swab a pustule or crust. This can be useful in selected patients (e.g., those with recurrent disease or treatment failure) to identify which bacteria (like Staphylococcus aureus or rarer gram-negative bacteria) are present and which antibiotics they might be sensitive to [5][6]. However, cultures can be negative, or they might only reveal harmless colonizing bacteria.
  4. Scalp Biopsy: This is an important confirmatory tool, especially when the diagnosis is uncertain [2][1]. A small “punch” of skin is taken from an active edge of a hairless patch, using local anesthetic. It may require a small stitch and leave a minor scar.

Decoding Your Biopsy Report

If a biopsy is performed, you might see technical terms that describe the destruction of the hair follicle [7]. Common findings in FD include:

  • Loss of Sebaceous Glands: The oil glands are often the first structures destroyed by inflammation [7].
  • Fused Infundibula: The upper parts of several hair follicles have merged together [7].
  • Mixed Inflammation: While FD was traditionally called a neutrophilic (neutrophil-heavy) condition, reports often show a “mixed” collection of immune cells, including plasma cells and lymphocytes [7][8].
  • Fibrosis: This is the medical term for the scar tissue that replaces the healthy follicle [9].

The “Look-Alikes”: Differential Diagnosis

FD belongs to a family of primary cicatricial alopecias (scarring hair loss). Your doctor must distinguish it from several “look-alikes”:

  • Dissecting Cellulitis: This condition features deep, painful, interconnected lumps or nodules that may drain fluid, rather than just surface pustules [10][11].
  • Lichen Planopilaris (LPP): LPP typically lacks the pustules of FD. Instead, it shows fine, white scaling (casts) that hugs the base of the hair and typically a lymphocytic pattern of inflammation under the microscope [12][13].
  • Acne Keloidalis Nuchae: This usually appears as firm, itchy bumps on the back of the neck that eventually turn into thick, keloid-like scars [14][15].

The Proposed FD-LPP Spectrum (FDLPPPS)

Sometimes, the diagnosis isn’t “either/or.” Doctors recognize a proposed middle ground known as the FD-LPP Phenotypic Spectrum (FDLPPPS) [16].

  • What it is: A term sometimes used when a patient shows features of both Folliculitis Decalvans (like tufted hairs and pustules) and Lichen Planopilaris (like white scaling and specific immune cell patterns) [16][17].
  • What it means: The clinical significance of this overlap is still debated. Identifying overlapping features does not automatically dictate a specific combination treatment. Instead, it signals that your management must be individualized, monitoring which symptoms are most active [16][17].

Understanding exactly what your tests show allows your doctor to move beyond a “one-size-fits-all” approach and tailor treatment to your scalp’s specific biology [1][16].

Common questions in this guide

How is folliculitis decalvans diagnosed?
Doctors usually combine a scalp examination with trichoscopy, which uses a dermatoscope to magnify the scalp and hair openings. If the diagnosis is uncertain, a small punch biopsy may be taken, and a culture may be considered when disease keeps returning or does not respond to treatment.
What can trichoscopy show in folliculitis decalvans?
Trichoscopy may show tufted hairs, meaning several hairs emerging from one opening, along with yellow tubular scale and red dots linked to active inflammation. These findings help the dermatologist assess the pattern and activity of scalp disease.
When is a scalp biopsy needed for folliculitis decalvans?
Not every patient needs a biopsy. When the diagnosis is uncertain, a dermatologist may use local anesthetic to remove a small punch of skin from the active edge of a hairless patch. The sample can help confirm the diagnosis, and the site may need a stitch or leave a small scar.
Can a bacterial culture confirm folliculitis decalvans?
A culture can identify bacteria in a pustule or crust and show which antibiotics may work, particularly when disease recurs or treatment has failed. A negative result or common skin bacteria does not by itself settle the diagnosis because cultures can miss bacteria or detect harmless colonizers.
How is folliculitis decalvans different from lichen planopilaris and other scarring hair-loss conditions?
Folliculitis decalvans more often features pustules, crusting, and tufted hairs, while lichen planopilaris more often causes fine white scale around the hair shaft and a different inflammation pattern on biopsy. Dissecting cellulitis tends to cause deep, painful interconnected lumps, and acne keloidalis nuchae usually causes firm, itchy bumps and thick scars at the back of the neck.
What does the FD-LPP phenotypic spectrum mean?
It describes cases with features of both folliculitis decalvans and lichen planopilaris, such as pustules or tufted hairs together with white scale or certain immune cells on biopsy. Its significance is still debated, so the term does not automatically mean a specific combination treatment; doctors monitor which features are most active and individualize care.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which areas of my scalp appear the most active, and do you recommend a biopsy at this time?
  2. 2.Did my trichoscopy show only tufted hairs, or were there also signs of other conditions, like scaling around the hair shafts?
  3. 3.What specific type of inflammation—neutrophilic, lymphocytic, or mixed—was found in my biopsy report?
  4. 4.If we do a culture and it is negative or shows common skin bacteria, how does that influence our choice of antibiotics?
  5. 5.Could I have an overlapping condition, and how would that change my individualized long-term treatment plan?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    Linear Circumscribed Scleroderma-Like Folliculitis Decalvans: Yet Another Face of a Protean Condition.

    Rezende HD, Dias MFRG, Kempf W, Treüb RM

    International journal of trichology 2018; (10(4)):175-179 doi:10.4103/ijt.ijt_9_18.

    PMID: 30386078
  2. 2

    Cross-sectional study to evaluate the utility of elastic tissue staining in primary cicatricial alopecia.

    Vishwanath T, Dhurat R

    Journal of clinical pathology 2024; (77(11)):737-742 doi:10.1136/jcp-2022-208745.

    PMID: 37553248
  3. 3

    Evaluation of a Handheld Dermatoscope in Clinical Diagnosis of Primary Cicatricial Alopecias.

    Karadag Köse Ö, Güleç AT

    Dermatology and therapy 2019; (9(3)):525-535 doi:10.1007/s13555-019-0304-3.

    PMID: 31190216
  4. 4

    Tufted hairs: A bouquet of flowers in different hair diseases.

    Starace M, Vezzoni R, Alessandrini A, et al.

    Journal of cosmetic dermatology 2022; (21(9)):3741-3746 doi:10.1111/jocd.14712.

    PMID: 35001495
  5. 5

    Gram-negative infections in patients with folliculitis decalvans: a subset of patients requiring alternative treatment.

    Samrao A, Mirmirani P

    Dermatology online journal 2020; (26(2)).

    PMID: 32239885
  6. 6

    Diagnostic delay, comorbid hidradenitis suppurativa and the prognostic value of bacterial culture in folliculitis decalvans: A cohort study.

    Lyakhovitsky A, Segal O, Galili E, et al.

    Journal der Deutschen Dermatologischen Gesellschaft = Journal of the German Society of Dermatology : JDDG 2023; (21(12)):1469-1477 doi:10.1111/ddg.15202.

    PMID: 37875786
  7. 7

    Histopathologic and dermoscopic features of 42 cases of folliculitis decalvans: A case series.

    Uchiyama M, Harada K, Tobita R, et al.

    Journal of the American Academy of Dermatology 2021; (85(5)):1185-1193 doi:10.1016/j.jaad.2020.03.092.

    PMID: 32272176
  8. 8

    Folliculitis decalvans-like pustular plaques on the limbs sparing the scalp.

    Yang A, Hannaford R, Kossard S

    The Australasian journal of dermatology 2020; (61(1)):54-56 doi:10.1111/ajd.13178.

    PMID: 31621894
  9. 9

    Compound Follicles in Folliculitis Decalvans Do Not Contain Vellus and Retained Telogen Follicles-A Pilot Histopathologic Series on Polytrichia.

    Lee J, Miteva M

    Journal of cutaneous pathology 2025; (52(1)):29-32 doi:10.1111/cup.14735.

    PMID: 39435542
  10. 10

    Dissecting folliculitis (dissecting cellulitis) of the scalp: a 66-patient case series and proposal of classification.

    Lee CN, Chen W, Hsu CK, et al.

    Journal der Deutschen Dermatologischen Gesellschaft = Journal of the German Society of Dermatology : JDDG 2018; (16(10)):1219-1226 doi:10.1111/ddg.13649.

    PMID: 30168900
  11. 11

    Management of folliculitis decalvans: The EADV task force on hair diseases position statement.

    Waśkiel-Burnat A, Starace M, Iorizzo M, et al.

    Journal of the European Academy of Dermatology and Venereology : JEADV 2025; (39(8)):1385-1394 doi:10.1111/jdv.20687.

    PMID: 40230058
  12. 12

    Clinical, Trichoscopic, and Histopathological Features of Primary Cicatricial Alopecias: A Retrospective Observational Study at a Tertiary Care Centre of North East India.

    Thakur BK, Verma S, Raphael V

    International journal of trichology 2015; (7(3)):107-12 doi:10.4103/0974-7753.167459.

    PMID: 26622153
  13. 13

    Lichen Planopilaris with Pustules: A Diagnostic Challenge.

    Morais KL, Martins CF, Anzai A, et al.

    Skin appendage disorders 2018; (4(2)):61-66 doi:10.1159/000478268.

    PMID: 29765960
  14. 14

    Unveiling a Shared Precursor Condition for Acne Keloidalis Nuchae and Primary Cicatricial Alopecias.

    Umar S, Ton D, Carter MJ, Shitabata P

    Clinical, cosmetic and investigational dermatology 2023; (16()):2315-2327 doi:10.2147/CCID.S422310.

    PMID: 37649568
  15. 15

    Profibrotic Subsets of SPP1+ Macrophages and POSTN+ Fibroblasts Contribute to Fibrotic Scarring in Acne Keloidalis.

    Hong YK, Hwang DY, Yang CC, et al.

    The Journal of investigative dermatology 2024; (144(7)):1491-1504.e10 doi:10.1016/j.jid.2023.12.014.

    PMID: 38218364
  16. 16

    Folliculitis Decalvans and Lichen Planopilaris Phenotypic Spectrum-A Series of 7 New Cases With Focus on Histopathology.

    Egger A, Stojadinovic O, Miteva M

    The American Journal of dermatopathology 2020; (42(3)):173-177 doi:10.1097/DAD.0000000000001595.

    PMID: 31855586
  17. 17

    Clinical Characterization and Treatment Response of Folliculitis Decalvans Lichen Planopilaris Phenotypic Spectrum: A Unicentre Retrospective Series of 31 Patients.

    Melián-Olivera A, Moreno-Arrones Ó, Burgos-Blasco P, et al.

    Acta dermato-venereologica 2024; (104()):adv12373 doi:10.2340/actadv.v104.12373.

    PMID: 38372472

This page is for informational purposes only and does not constitute medical advice. A dermatologist should interpret your examination, biopsy, trichoscopy, and culture results in the context of your symptoms.

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