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Glossary Hair Cortex

thickest hair layer, providing strength, elasticity, and color

The hair cortex is the thickest layer of a hair strand, located between the outer cuticle and the inner medulla. It contains long keratin filaments that give hair its strength, elasticity, and color, as it houses the pigment granules responsible for hair color. This layer is crucial for the hair's structural integrity and overall health.

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research Activation of the Notch pathway in the hair cortex leads to aberrant differentiation of the adjacent hair-shaft layers

109 citations , June 2000 in “Development”

This study reports that activating Notch signaling in the hair follicle cortex of transgenic mice caused abnormal differentiation of the medulla and cuticle, highlighting potential cell-cell interactions.

research A new mutation in the type II hair cortex keratin hHb1 involved in the inherited hair disorder monilethrix

100 citations , November 1997 in “Human Genetics”

In this study, researchers found that the prevalent Glu 410 Lys mutation in hHb6 and a new Glu 403 Lys mutation in hHb1 are linked to monilethrix, suggesting a mutational hotspot in type II hair keratins.

research hKAP1.6 and hKAP1.7, Two Novel Human High Sulfur Keratin-Associated Proteins are Expressed in the Hair Follicle Cortex

24 citations , February 2002 in “The journal of investigative dermatology/Journal of investigative dermatology”

In this study, researchers identified two new keratin-associated proteins, hKAP1.6 and hKAP1.7, in human hair follicles, contributing to understanding hair fiber differentiation.

research Investigation by Imaging Mass Spectrometry of Biomarker Candidates for Aging in the Hair Cortex

21 citations , October 2011 in “PloS one”

In this study, researchers identified three molecules in hair that varied with age, suggesting potential markers for aging and targets for cosmetic products.

research Pilomatricoma can differentiate not only towards hair matrix and hair cortex, but also follicular infundibulum, outer root sheath and hair bulge

18 citations , March 2009 in “Experimental Dermatology”

This study suggests that pilomatricoma can differentiate towards various hair follicle structures, including hair matrix, hair cortex, follicular infundibulum, outer root sheath, and hair bulge.

research Characterization of the Promoter Regions of Two Sheep Keratin-Associated Protein Genes for Hair Cortex-Specific Expression

14 citations , April 2016 in “PloS one”

This study found that the promoter region of the sheep KRTAP11-1 gene drives specific transcriptional activity in wool follicles, suggesting it may regulate hair keratinocyte specificity.

research The in vitro Assembly of Hair Follicle Keratins: Comparison of Cortex and Companion Layer Keratins

13 citations , January 2002 in “Biological chemistry”

This study found that hair follicle-specific keratins can form different structural assemblies depending on ionic conditions, with hair cortex keratins requiring physiological salt conditions to form intermediate filaments.

research Mutation detection of type II hair cortex keratin gene KRT86 in a Chinese Han family with congenital monilethrix

4 citations , August 2013 in “Chinese Medical Journal”

This study found that a mutation in the seventh exon of the KRT86 gene plays a major role in the pathogenesis of monilethrix in a Chinese family.

research Characterization of the mechanical properties of the cortex region of human hair fibers by multiparametric Atomic Force Microscopy mapping

May 2024 in “Ultramicroscopy”

Atomic Force Microscopy is a more accurate way to assess hair damage and the effect of cosmetic treatments.

research Thermal Induced Changes in Cuticle and Cortex to Chemically Treated Hair

December 2025 in “Biopolymers”

This study found that chemically treated hair, particularly when subjected to both acid straightening and bleaching, experiences more significant structural damage when exposed to heat, highlighting key changes in both the internal and surface components of hair fibers.

research Cortexolone 17a-propionate: A new antiandrogen acting on hair dermal papilla cells for the treatment of androgenic alopecia

March 2014 in “Journal of The American Academy of Dermatology”

Cortexolone 17a-propionate may be an effective new treatment for hair loss.

research Context-dependent effect of sPLA2-IIA induced proliferation on murine hair follicle stem cells and human epithelial cancer

13 citations , September 2019 in “EBioMedicine”

This study found that Secretory Phospholipase A2-IIA (sPLA2-IIA) promotes proliferation through JNK/c-Jun signaling, distinctively affecting normal stem cells and cancer cells, suggesting it as a potential target for cancer treatment.

research A highly resistant structure between cuticle and cortex of human hair

10 citations , November 2016 in “International Journal of Cosmetic Science”

This study proposed the existence of a membrane-like structure between the cuticle and cortex in human hair, which may provide strong protection against external stimuli.

research A highly resistant structure between the cuticle and the cortex of human hair. II. CARB, a penetration barrier

6 citations , December 2018 in “International Journal of Cosmetic Science”

This study found that a highly resistant structure, located at the interface between the cuticle and cortex of human hair, acts as a penetration barrier, which the authors propose to name the "cuticle anchored resistant base" or CARB.

research Transmission electron microscopy staining methods for the cortex of human hair: a modified osmium method and comparison with other stains

29 citations , April 2011 in “Journal of Microscopy”

This study describes a modified reduction-osmication method for staining human scalp hair that improves reagent penetration and visualization of hair cortex features using transmission electron microscopy.

research Mutation of the doublecortin gene in male patients with double cortex syndrome: Somatic mosaicism detected by hair root analysis

43 citations , September 2001 in “Annals of Neurology”

This study found that somatic mosaic mutations in the doublecortin gene may cause subcortical band heterotopia in male patients, and molecular analysis using hair roots is a useful detection method.

research Mutations in the hair cortex keratin hHb6 cause the inherited hair disease monilethrix

175 citations , August 1997 in “Nature Genetics”

research Three-dimensional architecture of macrofibrils in the human scalp hair cortex

55 citations , February 2014 in “Journal of Structural Biology”

This study observed that human hair macrofibrils predominantly exhibit a double-twist architecture with varying inter-macrofibril angles, advancing insights into their structural organization and mechanical implications.

research Nanoindentation of Hair Cortex and Medulla Regions

3 citations , July 2019 in “Fibers And Polymers/Fibers and polymers”

research Data from: Social hair plucking across affiliative and agonistic contexts, with health considerations, in captive rhesus macaques (Macaca mulatta)

June 2026 in “DRYAD”

This study found that social hair plucking in captive rhesus macaques may share traits with both prosocial and aggressive behaviors and is associated with alopecia and hair cortisol levels.

research A discrete transition zone between cuticle and cortex layers of a human hair fibre: changes observed in the presence of breast cancer

1 citations , October 2017 in “ecancermedicalscience”

This study observed that the molecular structure of keratins in hair fibres' discrete transition zone differs in breast cancer patients, with altered lipid ester absorption bands reverting post-cancer removal.

research 574 Murine sebaceous gland homeostasis requires intact cutaneous innervation in a hair cycle-dependent context

September 2019 in “The journal of investigative dermatology/Journal of investigative dermatology”

In this study, mouse sebaceous glands were found to require nerves for growth during active hair cycles, suggesting a nerve-dependent sebaceous gland cycle coordinated with hair growth.

research Mechanical properties characterization of human hair fibers cortex region by multiparametric Atomic Force Microscopy mapping

October 2021 in “Digital Library of Theses and Dissertations (Universidade de São Paulo)”

This study found that applying a cosmetic active ingredient improved the Young's modulus of chemically damaged human hair fibers, suggesting enhanced mechanical properties compared to untreated fibers.

research Keratin 17 Expression in the Hard Epithelial Context of the Hair and Nail, and its Relevance for the Pachyonychia Congenita Phenotype

88 citations , June 2000 in “Journal of Investigative Dermatology”

Keratin 17 is important for hair and nail structure and affects pachyonychia congenita symptoms.

research Impact of ultraviolet radiation‐induced damage to hair fiber integrity: A multi‐technique physicochemical characterization of surface and cortex properties

May 2026 in “International Journal of Cosmetic Science”

This study found that UV radiation exposure during a simulated Brazilian summer caused more significant mechanical damage to natural hair than bleaching, although both caused comparable structural alterations, with double bleaching leading to the most severe protein degradation.

research Caffeine as an Active Molecule in Cosmetic Products for Hair Loss: Its Mechanisms of Action in the Context of Hair Physiology and Pathology

January 2025 in “Molecules”

In this review, the authors discuss caffeine's potential mechanisms and benefits as a hair loss treatment, noting its possible effectiveness and safety, though they caution that existing studies often have significant design flaws.

research Zinc deficiency or genetic mutations?—A case report of hair heterochromia in the context of MC1R genetic mutations

January 2024 in “Australasian journal of dermatology (Print)”

In this case study, researchers documented a Chinese boy with hair color changing to red and identified MC1R genetic mutations as the cause, rather than zinc deficiency, enhancing our understanding of hair heterochromia due to genetic factors.

research Impact of acid (”progressive brush”) and alkaline straightening on the hair fiber: Differential effects on the cuticle and cortex properties

November 2022 in “International journal of trichology”

This study found that glyoxylic acid caused more protein loss in hair compared to traditional alkaline straighteners, though both types of treatments showed comparable effects on hair tensile strength.

research Micrografting in Extensive Quantities Please Note: In 1995 we began using Follicular Unit Transplantation for all hair restoration procedures performed at NHI. Minigrafting/micrografting techniques were discontinued at this time. This article should be read in that context.

January 1995

Since 1995, we only use Follicular Unit Transplantation for hair restoration and stopped using minigrafting/micrografting techniques.

research The Catalog of Human Hair Keratins

272 citations , September 2001 in “Journal of Biological Chemistry”

This study cataloged human type II hair keratins, detailing their expression and differentiation roles in hair follicles and comparing them with type I keratins to explore keratin-pairing principles.