Skin nonmelanocytic tumor
Benign (nonmelanotic) epidermal tumors or tumor-like lesions
Inverted follicular keratosis

Topic Completed: 1 September 2017

Minor changes: 13 December 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Inverted follicular keratosis [title]

Andrew L.J. Dunn, M.D.
Sara C. Shalin, M.D., Ph.D.
Page views in 2019: 15,060
Page views in 2020 to date: 7,079
Cite this page: Dunn ALJ, Shalin SC. Inverted follicular keratosis. website. Accessed July 8th, 2020.
Definition / general
  • Found on the head and neck
  • Usually affects older males
Essential features
  • Benign, usually endophytic proliferation of follicular infundibulum with squamous eddies
  • IFK
  • Older men
  • Predominantly head and neck
  • May be irritated seborrheic keratosis, irritated verruca vulgaris or keratotic lesion that involves the infundibular region of hair follicle
Case reports
  • Not necessary; biopsy is usually curative
Clinical images

Images hosted on other servers:

8 - 12 mm pedunculated nodule

Gross description
  • Solitary skin colored papule with or without filiform growth measuring less than 1 cm
Microscopic (histologic) description
  • Patterns include:
    • Wart-like variant
    • Keratoacanthoma-like pattern
    • Solid nodular
  • Well circumscribed endophytic growth of squamous cells with lobular extension into the dermis; exophytic lesions with a keratoacanthoma-like appearance have been described
  • Variable number of squamous eddies; may be increased secondary to irritation
  • Peripheral basaloid cells with occasional mitotic activfty
Microscopic (histologic) images

Contributed by Andrew L.J. Dunn

Various magnifications

Warty-like variant

Images hosted on other servers:

Various images

Positive stains
Board review style question #1
Which of the following is true about inverted follicular keratosis?

  1. BCL2 is downregulated in dendritic cells
  2. Squamous eddies are an atypical finding in inverted follicular keratosis
  3. These lesions are more commonly found on the head and neck
  4. These lesions are more common in young women
Board review answer #1
C. These lesions are more commonly found on the head and neck

BCL2 has been found to be upregulated in the dendritic cells of IFKs but not seborrhea keratosis. IFKs are typically found on the head and neck of older males. Squamous eddies are a usual finding in IFKs.

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