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Glossary Inner Root Sheath

layer of cells supporting and shaping the growing hair shaft

The Inner Root Sheath (IRS) is a layer of cells that surrounds and supports the growing hair shaft within the hair follicle. It plays a crucial role in shaping the hair and guiding it as it emerges from the scalp. The IRS is composed of three distinct layers: Henle's layer, Huxley's layer, and the cuticle of the inner root sheath, each contributing to the structural integrity and function of the hair follicle.

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research K6irs1, K6irs2, K6irs3, and K6irs4 Represent the Inner-Root-Sheath-Specific Type II Epithelial Keratins of the Human Hair Follicle1

130 citations , April 2003 in “Journal of Investigative Dermatology”

This study reports the cloning and expression details of two new human type II keratins, K6irs3 and K6irs4, in the hair follicle's inner root sheath, suggesting a distinct functional role related to hair structure.

research K25 (K25irs1), K26 (K25irs2), K27 (K25irs3), and K28 (K25irs4) Represent the Type I Inner Root Sheath Keratins of the Human Hair Follicle

93 citations , July 2006 in “Journal of Investigative Dermatology”

This study describes the expression patterns of type I inner root sheath keratin proteins K25–K28 in human hair follicles, highlighting their distinct distribution within different layers.

research A Novel Epithelial Keratin, hK6irs1, is Expressed Differentially in All Layers of the Inner Root Sheath, Including Specialized Huxley Cells (Flügelzellen) of the Human Hair Follicle

86 citations , May 2002 in “Journal of Investigative Dermatology”

This study characterized a new human keratin, hK6irs1, specifically found in the inner root sheath of hair follicles, which suggests its role in the structural integrity and guidance of growing hair shafts.

research Abnormal inner root sheath of the hair follicle in the loose anagen hair syndrome: An ultrastructural study

31 citations , December 2010 in “Journal of the American Academy of Dermatology”

This study reports that structural abnormalities in the inner root sheath of hair follicles may cause the hair shaft to be loosely attached in patients with loose anagen hair syndrome.

Structural Features of the Alpha-Type Filaments of the Inner Root Sheath Cells of the Guinea Pig Hair Follicle

research Structural features of the α-type filaments of the inner root sheath cells of the guinea pig hair follicle

24 citations , November 1978 in “Biochemistry”

This paper reports on the structural characteristics of α-type filaments in the inner root sheath cells of guinea pig hair follicles without presenting new clinical findings.

Fine Structure and Immunocytochemistry of Monotreme Hairs, with Emphasis on the Inner Root Sheath and Trichohyalin-Based Cornification During Hair Evolution

research Fine structure and immunocytochemistry of monotreme hairs, with emphasis on the inner root sheath and trichohyalin‐based cornification during hair evolution

15 citations , July 2004 in “Journal of morphology”

This study analyzes the fine structure and protein distribution in monotreme hairs, finding similarities with other mammals and detailing unique immunocytochemical features in their inner root sheaths.

research Fine structure of marsupial hairs, with emphasis on trichohyalin and the structure of the inner root sheath

8 citations , July 2004 in “Journal of morphology”

This study explored the structure and keratin composition of marsupial hairs, finding similarities in keratin localization to hairs in placental mammals, and highlighting potential roles of trichohyalin and transglutaminase during hair development and shedding.

research A Novel Type II Cytokeratin, mK6irs, is Expressed in the Huxley and Henle Layers of the Mouse Inner Root Sheath

45 citations , March 2001 in “Journal of Investigative Dermatology”

This study identified a new cytokeratin, mK6irs, specifically expressed in the inner root sheath of mouse hair follicles, distinguishing it as a member of the type II cytokeratin family.

research Keratins 1 and 10 or homologues as regular constituents of inner root sheath and cuticle cells in the human hair follicle.

44 citations , August 1990 in “PubMed”

This study provides evidence for K1 and K10 derivatives' presence in the inner root sheath and hair cuticle, suggesting that these hair follicle parts may follow familiar keratinization principles.

research Keratin K6irs is specific to the inner root sheath of hair follicles in mice and humans

38 citations , October 2001 in “British Journal of Dermatology”

This study identified a new keratin, K6irs, as a potential histological marker for the inner root sheath of hair follicles in mice and humans, and as a candidate gene for hereditary hair defects.

research Investigation of the hair follicle inner root sheath in scarring and non‐scarring alopecia

28 citations , June 2007 in “Journal of Cutaneous Pathology”

This study found that premature desquamation of the inner root sheath is a non-specific histologic feature in scarring alopecia and cannot be used alone to define central centrifugal cicatricial alopecia.

research Functional analysis of keratin components in the mouse hair follicle inner root sheath

23 citations , February 2004 in “British Journal of Dermatology”

Keratin in mouse hair follicles is complex and plays specific roles.

research Heparanase 1: a key participant of inner root sheath differentiation program and hair follicle homeostasis

22 citations , June 2008 in “Experimental Dermatology”

This study found that heparanase is primarily located in the inner root sheath of human hair follicles during the anagen phase, and inhibiting it in cultured hair follicles induces a catagen-like process.

research μ-Crystallin, Thyroid Hormone-binding Protein, is Expressed Abundantly in the Murine Inner Root Sheath Cells

22 citations , September 2000 in “Journal of Investigative Dermatology”

This study found that mu-crystallin gene expression in mouse skin is highest during the anagen phase of hair development, suggesting its possible role in hair follicle growth.

research Comparative aspects of the inner root sheath in adult and developing hairs of mammals in relation to the evolution of hairs

20 citations , September 2004 in “Journal of Anatomy”

This study suggests that the structure and function of the inner root sheath in mammalian hair may have evolved from simpler forms seen in monotremes, aiding in hair exit without damaging the epidermis.

research Hairless Plays a Role in Formation of Inner Root Sheath via Regulation of Dlx3 Gene

17 citations , March 2012 in “Journal of biological chemistry/The Journal of biological chemistry”

In this study, researchers found that overexpression of the hairless protein in Hr mutant mice disrupts inner root sheath formation by downregulating Dlx3 and associated keratins in hair follicle development.

research Synthesis of porcine pCLCA2 protein during late differentiation of keratinocytes of epidermis and hair follicle inner root sheath

13 citations , September 2012 in “Cell & tissue research/Cell and tissue research”

In this study, researchers found that the pCLCA2 protein is expressed in specific areas of pig skin, but its role in skin structure or function remains unclear.

research Immunolocalization of junctional proteins in human hairs indicates that the membrane complex stabilizes the inner root sheath while desmosomes contact the companion layer through specific keratins

12 citations , January 2013 in “Acta Histochemica”

Junctional proteins stabilize the inner root sheath and connect the companion layer in human hair.

research Pili Trianguli et Canaliculi Is a Defect of Inner Root Sheath Keratinization

8 citations , May 2005 in “The American journal of dermatopathology/American journal of dermatopathology”

This study observed unique ultrastructural changes in a 4-year-old girl with pili trianguli et canaliculi that may affect hair shaft surface characteristics due to inner root sheath alterations.

Ultrastructural Immunolocalization of Involucrin in the Medulla and Inner Root Sheath of Human Hair

research Ultrastructural immunolocalization of involucrin in the medulla and inner root sheath of the human hair

7 citations , December 2011 in “Annals of anatomy”

This study found that involucrin likely plays a key role in forming the cornified material of the medulla and inner root sheath of human hair, contributing to its mechanical strength.

Premature Desquamation of the Inner Root Sheath in Noninflamed Hair Follicles as a Specific Marker for Central Centrifugal Cicatricial Alopecia

research Premature Desquamation of the Inner Root Sheath in Noninflamed Hair Follicles as a Specific Marker for Central Centrifugal Cicatricial Alopecia

6 citations , December 2018 in “The American Journal of Dermatopathology”

This study found that the presence of premature desquamation of the inner root sheath in noninflamed hair follicles is a relatively specific marker for diagnosing central centrifugal cicatricial alopecia.

research Cytochemistry of Trichohyalin Granules: A Possible Role for Cornification of Inner Root Sheath Cell in the Hair Follicle

4 citations , April 1989 in “The Journal of Dermatology”

This study observed in mouse skin that trichohyalin granules in hair follicles transform into filamentous structures as inner root sheath cells differentiate and cornify.

research A KRT71 Loss-of-Function Variant Results in Inner Root Sheath Dysplasia and Recessive Congenital Hypotrichosis of Hereford Cattle

2 citations , July 2021 in “Genes”

This study identified a new genetic variant in the KRT71 gene responsible for a breed-specific form of hypotrichosis in Hereford cattle, potentially serving as a model for similar human conditions.

research Four murine monoclonal antibodies specific for the inner root sheath in the human hair follicle

1 citations , January 1989

This study produced and characterized four new monoclonal antibodies that specifically recognize differentiation antigens in human hair follicle and epidermal structures.

research Hair-raising Mysteries of the Inner Root Sheath: Unearthing Treasures in Bald Spots

June 2025

This review suggests that the inner root sheath of human hair follicles may have broader regulatory roles beyond structural support, potentially impacting processes like folliculogenesis, anagen phase regulation, and immunomodulation.

research Study on the expression patterns of inner root sheath-specific genes in Tan sheep hair follicle during different developmental stages

July 2024 in “Gene”

This study analyzed inner root sheath-specific genes in Tan sheep during various growth stages, finding peak expression at birth. The pattern of genes KRT71, KRT72, and TCHH is consistent with wool crimp, potentially influencing wool morphology.