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Keratinocytes are the primary type of
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
found in the
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referred to as basal keratinocytes. Keratinocytes form a barrier against environmental damage by heat,
UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...
, water loss, pathogenic bacteria, fungi,
parasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
, and viruses. A number of structural proteins,
enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
, lipids, and
antimicrobial peptides Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for an ...
contribute to maintain the important barrier function of the skin. Keratinocytes differentiate from epidermal stem cells in the lower part of the epidermis and migrate towards the surface, finally becoming
corneocytes Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for ...
and eventually be shed off, which happens every 40 to 56 days in humans.


Function

The primary function of keratinocytes is the formation of a barrier against environmental damage by heat,
UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...
, water loss, pathogenic bacteria, fungi,
parasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
, and viruses. Pathogens invading the upper layers of the epidermis can cause keratinocytes to produce proinflammatory mediators, particularly
chemokines Chemokines (), or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In additi ...
such as
CXCL10 C-X-C motif chemokine ligand 10 (CXCL10) also known as Interferon gamma-induced protein 10 (IP-10) or small-inducible cytokine B10 is an 8.7 kDa protein that in humans is encoded by the ''CXCL10'' gene. C-X-C motif chemokine 10 is a small cytokin ...
and
CCL2 ''For the ICAO airport code see Candle Lake Airpark, for the diradical compound see Dichlorocarbene.'' The chemokine (C-C motif) ligand 2 (CCL2) is also referred to as monocyte chemoattractant protein 1 (MCP1) and small inducible cytokine A2. CC ...
(MCP-1) which attract monocytes, natural killer cells,
T-lymphocytes A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...
, and dendritic cells to the site of pathogen invasion.


Structure

A number of structural proteins (
filaggrin Filaggrin (filament aggregating protein) is a filament-associated protein that binds to keratin fibers in epithelial cells. Ten to twelve filaggrin units are post-translationally hydrolyzed from a large profilaggrin precursor protein during termi ...
, keratin),
enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
(
proteases A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the form ...
), lipids, and
antimicrobial peptides Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for an ...
(
defensins Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate and invertebrate animals, plants, and fungi. They are host defense peptides, with members displaying either direct antimicrobial activity, immune sign ...
) contribute to maintain the important barrier function of the skin. Keratinization is part of the physical barrier formation (
cornification Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, hor ...
), in which the keratinocytes produce more and more keratin and undergo terminal differentiation. The fully cornified keratinocytes that form the outermost layer are constantly shed off and replaced by new cells.


Cell differentiation

Epidermal stem cells reside in the lower part of the epidermis (stratum basale) and are attached to the basement membrane through
hemidesmosome Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy, however, desmosomes attach ...
s. Epidermal stem cells divide in a random manner yielding either more stem cells or transit amplifying cells. Some of the transit amplifying cells continue to proliferate then commit to differentiate and migrate towards the surface of the epidermis. Those stem cells and their differentiated progeny are organized into columns named epidermal proliferation units. During this differentiation process, keratinocytes permanently withdraw from the
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and subs ...
, initiate expression of epidermal differentiation markers, and move suprabasally as they become part of the stratum spinosum, stratum granulosum, and eventually
corneocyte Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for ...
s in the
stratum corneum The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compac ...
. Corneocytes are keratinocytes that have completed their differentiation program and have lost their
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
and
cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...
ic
organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
. Corneocytes will eventually be shed off through
desquamation Desquamation occurs when the outermost layer of a tissue, such as the skin, is shed. The term is . Physiologic desquamation Keratinocytes are the predominant cells of the epidermis, the outermost layer of the skin. Living keratinocytes reside in ...
as new ones come in. At each stage of differentiation, keratinocytes express specific
keratins Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, h ...
, such as
keratin 1 Keratin 1 is a Type II intermediate filament (IFs) of the intracytoplasmatic cytoskeleton. Is co-expressed with and binds to Keratin 10, a Type I keratin, to form a coiled coil heterotypic keratin chain. Keratin 1 and Keratin 10 are specifically ex ...
,
keratin 5 Keratin 5, also known as KRT5, K5, or CK5, is a protein that is encoded in humans by the ''KRT5'' gene. It dimerizes with keratin 14 and forms the intermediate filaments (IF) that make up the cytoskeleton of basal epithelial cells. This protein ...
,
keratin 10 Keratin, type I cytoskeletal 10 also known as cytokeratin-10 (CK-10) or keratin-10 (K10) is a protein that in humans is encoded by the ''KRT10'' gene. Keratin 10 is a type I keratin. Function Keratin-10 is a member of the type I (acidic) cyto ...
, and
keratin 14 Keratin 14 is a member of the type I keratin family of intermediate filament proteins. Keratin 14 was the first type I keratin sequence determined. Keratin 14 is also known as cytokeratin-14 (CK-14) or keratin-14 (KRT14). In humans it is encoded ...
, but also other markers such as
involucrin Involucrin is a protein component of human skin and in humans is encoded by the ''IVL'' gene. In binding the protein loricrin, involucrin contributes to the formation of a cell envelope that protects corneocytes in the skin. Gene This gene ...
,
loricrin Loricrin is a protein that in humans is encoded by the ''LOR'' gene. Function Loricrin is a major protein component of the cornified cell envelope found in terminally differentiated epidermal cells. Loricrin is expressed in the granular laye ...
,
transglutaminase Transglutaminases are enzymes that in nature primarily catalyze the formation of an isopeptide bond between γ-carboxamide groups ( -(C=O)NH2 ) of glutamine residue side chains and the ε-amino groups ( -NH2 ) of lysine residue side ...
, filaggrin, and caspase 14. In humans, it is estimated that keratinocytes
turn over ''Turn Over'' is the first live album of the Japanese rock group Show-Ya. It is a collection of live songs recorded during concerts from the "Date Line Tour" and "Immigration Tour" in 1987, and from the "Tour of the Immigrant" in 1988. The album ...
from stem cells to desquamation every 40–56 days, whereas in mice the estimated
turnover time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...
is 8–10 days. Factors promoting keratinocyte differentiation are: * A
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
gradient, with the lowest concentration in the stratum basale and increasing concentrations until the outer stratum granulosum, where it reaches its maximum. Calcium concentration in the stratum corneum is very high in part because those relatively dry cells are not able to dissolve the ions. Those elevations of extracellular calcium concentrations induces an increase in
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
free calcium concentrations in keratinocytes. Part of that intracellular calcium increase comes from calcium released from intracellular stores and another part comes from transmembrane calcium influx, through both calcium-sensitive
chloride channels Chloride channels are a superfamily of poorly understood ion channels specific for chloride. These channels may conduct many different ions, but are named for chloride because its concentration ''in vivo'' is much higher than other anions. Several ...
and voltage-independent cation channels permeable to calcium. Moreover, it has been suggested that an extracellular calcium-sensing
receptor Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...
(CaSR) also contributes to the rise in intracellular calcium concentration. * Vitamin D3 (cholecalciferol) regulates keratinocyte proliferation and differentiation mostly by modulating calcium concentrations and regulating the expression of genes involved in keratinocyte differentiation. Keratinocytes are the only cells in the body with the entire vitamin D metabolic pathway from vitamin D production to
catabolism Catabolism () is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy or used in other anabolic reactions. Catabolism breaks down large molecules (such as polysaccharides, lipids, ...
and
vitamin D receptor The vitamin D receptor (VDR also known as the calcitriol receptor) is a member of the nuclear receptor family of transcription factors. Calcitriol (the active form of vitamin D, 1,25-(OH)2vitamin D3) binds to VDR, which then forms a heterod ...
expression. *
Cathepsin E Cathepsin E is an enzyme () that in humans is encoded by the ''CTSE'' gene. The enzyme is also known as ''slow-moving proteinase'', ''erythrocyte membrane aspartic proteinase'', ''SMP'', ''EMAP'', ''non-pepsin proteinase'', ''cathepsin D-like aci ...
. * TALE
homeodomain A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full-g ...
transcription factors In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...
. *
Hydrocortisone Hydrocortisone is the name for the hormone cortisol when supplied as a medication. Uses include conditions such as adrenocortical insufficiency, adrenogenital syndrome, high blood calcium, thyroiditis, rheumatoid arthritis, dermatitis, asthma, ...
. Since keratinocyte differentiation inhibits keratinocyte proliferation, factors that promote keratinocyte proliferation should be considered as preventing differentiation. These factors include: * The transcription factor p63, which prevents epidermal stem cells from differentiating into keratinocytes. Mutations in the p63 DNA-binding domain are associated with ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome. The transcriptome of p63 mutant keratinocytes deviated from the normal epidermal cell identity. * Vitamin A and its analogues. * Epidermal growth factor. *
Transforming growth factor alpha Transforming growth factor alpha (TGF-α) is a protein that in humans is encoded by the TGFA gene. As a member of the epidermal growth factor (EGF) family, TGF-α is a mitogenic polypeptide. The protein becomes activated when binding to receptors ...
. *
Cholera toxin Cholera toxin (also known as choleragen and sometimes abbreviated to CTX, Ctx or CT) is AB5 multimeric protein complex secreted by the bacterium ''Vibrio cholerae''. CTX is responsible for the massive, watery diarrhea characteristic of cholera i ...
.


Interaction with other cells

Within the epidermis keratinocytes are associated with other cell types such as
melanocytes Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart. Mel ...
and Langerhans cells. Keratinocytes form
tight junction Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epith ...
s with the nerves of the skin and hold the Langerhans cells and intra-dermal lymphocytes in position within the epidermis. Keratinocytes also modulate the immune system: apart from the above-mentioned
antimicrobial peptides Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for an ...
and
chemokines Chemokines (), or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In additi ...
they are also potent producers of anti-inflammatory mediators such as IL-10 and
TGF-β Transforming growth factor beta (TGF-β) is a multifunctional cytokine belonging to the transforming growth factor superfamily that includes three different mammalian isoforms (TGF-β 1 to 3, HGNC symbols TGFB1, TGFB2, TGFB3) and many other s ...
. When activated, they can stimulate
cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...
inflammation and Langerhans cell activation via
TNFα Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...
and
IL-1β Interleukin-1 beta (IL-1β) also known as leukocytic pyrogen, leukocytic endogenous mediator, mononuclear cell factor, lymphocyte activating factor and other names, is a cytokine protein that in humans is encoded by the ''IL1B'' gene."Catabolin ...
secretion. Keratinocytes contribute to protecting the body from ultraviolet radiation (UVR) by taking up melanosomes, vesicles containing the endogenous photoprotectant
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
, from epidermal melanocytes. Each melanocyte in the epidermis has several
dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...
s that stretch out to connect it with many keratinocytes. The melanin is then stored within keratinocytes and melanocytes in the perinuclear area as supranuclear “caps”, where it protects the DNA from UVR-induced
damage Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a system that adversely affect its current or future performance".Farrar, C.R., Sohn, H., ...
.


Role in wound healing

Wounds to the skin will be repaired in part by the migration of keratinocytes to fill in the gap created by the wound. The first set of keratinocytes to participate in that repair come from the bulge region of the
hair follicle The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between h ...
and will only survive transiently. Within the healed epidermis they will be replaced by keratinocytes originating from the epidermis. At the opposite, epidermal keratinocytes, can contribute to ''de novo'' hair follicle formation during the healing of large wounds. Functional keratinocytes are needed for tympanic perforation healing.


Sunburn cells

A sunburn
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
is a keratinocyte with a pyknotic
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
and eosinophilic
cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...
that appears after exposure to UVC or
UVB Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
radiation or
UVA UVA most often refers to: * Ultraviolet A, a type of ultraviolet radiation * University of Virginia, a public research university in Charlottesville, Virginia, United States Uva or UVA may also refer to: Places * Uva, Missouri, an unincorpora ...
in the presence of
psoralen Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered a ...
s. It shows premature and abnormal
keratinization Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, hor ...
, and has been described as an example of
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes includ ...
.


Aging

With age, tissue
homeostasis In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and i ...
declines partly because stem/progenitor cells fail to self-renew or differentiate. DNA damage caused by exposure of stem/progenitor cells to reactive oxygen species (ROS) may play a key role in epidermal stem cell aging. Mitochondrial superoxide dismutase (
SOD2 Superoxide dismutase 2, mitochondrial (SOD2), also known as manganese-dependent superoxide dismutase (MnSOD), is an enzyme which in humans is encoded by the ''SOD2'' gene on chromosome 6. A related pseudogene has been identified on chromosome 1. ...
) ordinarily protects against ROS. Loss of SOD2 in mouse epidermal cells was observed to cause cellular senescence that irreversibly arrested proliferation in a fraction of keratinocytes. In older mice, SOD2 deficiency delayed
wound A wound is a rapid onset of injury that involves lacerated or punctured skin (an ''open'' wound), or a contusion (a ''closed'' wound) from blunt force trauma or compression. In pathology, a ''wound'' is an acute injury that damages the epider ...
closure and reduced epidermal thickness.


Civatte body

A Civatte body (named after the French dermatologist Achille Civatte, 1877–1956) is a damaged basal keratinocyte that has undergone
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes includ ...
, and consist largely of keratin intermediate filaments, and are almost invariably covered with immunoglobulins, mainly IgM. Civatte bodies are characteristically found in skin lesions of various dermatoses, particularly
lichen planus Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, and is only named that because it looks like one. It is characterized by polygonal, fl ...
and
discoid lupus erythematosus Discoid lupus erythematosus is the most common type of chronic cutaneous lupus (CCLE), an autoimmune skin condition on the lupus erythematosus spectrum of illnesses. It presents with red, painful, inflamed and coin-shaped patches of skin with a sc ...
. They may also be found in graft-versus-host disease,
adverse drug reaction An adverse drug reaction (ADR) is a harmful, unintended result caused by taking medication. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs. The meaning of this term ...
s, inflammatory keratosis (such as lichenoid
actinic keratosis Actinic keratosis (AK), sometimes called solar keratosis or senile keratosis, is a pre-cancerous area of thick, scaly, or crusty skin.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . Actinic k ...
and
lichen planus Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, and is only named that because it looks like one. It is characterized by polygonal, fl ...
-like keratosis),
erythema multiforme Erythema multiforme (EM) is a skin condition that appears with red patches evolving into target lesions, typically on both hands. It is a type of erythema possibly mediated by deposition of immune complexes (mostly IgM-bound complexes) in the ...
,
bullous pemphigoid Bullous pemphigoid (type of pemphigoid) is an autoimmune pruritic skin disease which typically occurs in people aged over 60, that may involve the formation of blisters ( bullae) in the space between the epidermal and dermal skin layers. It is cl ...
,
eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
,
lichen planopilaris Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, and is only named that because it looks like one. It is characterized by polygonal, fl ...
, febrile neutrophilic dermatosis,
toxic epidermal necrolysis Toxic epidermal necrolysis (TEN) is a type of severe skin reaction. Together with Stevens–Johnson syndrome (SJS) it forms a spectrum of disease, with TEN being more severe. Early symptoms include fever and flu-like symptoms. A few days later t ...
,
herpes simplex Herpes simplex is a viral infection caused by the herpes simplex virus. Infections are categorized based on the part of the body infected. Oral herpes involves the face or mouth. It may result in small blisters in groups often called cold ...
and varicella zoster lesions, dermatitis herpetiformis, porphyria cutanea tarda,
sarcoidosis Sarcoidosis (also known as ''Besnier-Boeck-Schaumann disease'') is a disease involving abnormal collections of inflammatory cells that form lumps known as granulomata. The disease usually begins in the lungs, skin, or lymph nodes. Less commonly a ...
, subcorneal pustular dermatosis,
transient acantholytic dermatosis Grover's disease (GD) is a polymorphic, pruritic, papulovesicular dermatosis characterized histologically by acantholysisFreedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . with or without dysk ...
and epidermolytic hyperkeratosis.


See also

*
Epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
* Skin *
Corneocyte Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for ...
* Keratin * HaCaT * List of human cell types derived from the germ layers * Epidermidibacterium keratini


References


External links

* {{Skin Layers and Appendages Skin anatomy Sequestering cells Human cells