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Dermis
Dermis
Dermis
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Dermis
Cross-section of human skin
Cross section of skin under a microscope
Details
Part ofSkin
Identifiers
MeSHD020405
TA98A16.0.00.010
TA27047
THH3.12.00.1.03001
FMA70323
Anatomical terminology

The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided into two layers, the superficial area adjacent to the epidermis called the papillary region and a deep thicker area known as the reticular dermis.[1] The dermis is tightly connected to the epidermis through a basement membrane. Structural components of the dermis are collagen, elastic fibers, and extrafibrillar matrix.[2] It also contains mechanoreceptors that provide the sense of touch and thermoreceptors that provide the sense of heat. In addition, hair follicles, sweat glands, sebaceous glands (oil glands), apocrine glands, lymphatic vessels, nerves and blood vessels are present in the dermis. Those blood vessels provide nourishment and waste removal for both dermal and epidermal cells.

Structure

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The dermis is composed of three major types of cells:[3] fibroblasts, macrophages, and mast cells.

Apart from these cells, the dermis is also composed of matrix components such as collagen (which provides strength), elastin (which provides elasticity), and extrafibrillar matrix, an extracellular gel-like substance primarily composed of glycosaminoglycans (most notably hyaluronan), proteoglycans, and glycoproteins.[3]

Layers

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Illustration of dermal circulation and layers

Papillary dermis

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The papillary dermis is the uppermost layer of the dermis. It intertwines with the rete ridges of the epidermis and is composed of fine and loosely arranged collagen fibers.[2] The papillary region is composed of loose areolar connective tissue. It is named for its fingerlike projections called papillae or dermal papillae specifically, that extend toward the epidermis and contain either terminal networks of blood capillaries or tactile Meissner's corpuscles.[4]

  • Epidermis, papillary dermis and reticular dermis.
    Epidermis, papillary dermis and reticular dermis.

Dermal papillae

[edit]
Dermal papillae
Papilla of the hand, treated with acetic acid. Magnified 350 times.

A. Side view of a papilla of the hand.
a. Cortical layer.
b. Tactile corpuscle.
c. Small nerve of the papilla, with neurolemma.
d. Its two nervous fibers running in spiral coils around the tactile corpuscle.
e. Apparent termination of one of these fibers.

B. Tactile papilla seen from above so as to show its transverse section.
a. Cortical layer.
b. Nerve fiber.
c. Outer layer of the tactile body, with nuclei.
d. Clear interior substance.
Details
Identifiers
Latinpapillae dermis
MeSHD020405
TA98A16.0.00.010
TA27047
THH3.12.00.1.03001
FMA70323
Anatomical terminology

The dermal papillae (DP; singular papilla, diminutive of Latin papula, 'pimple') are small, nipple-like extensions (or interdigitations) of the dermis into the epidermis. At the surface of the skin in hands and feet, they appear as epidermal, papillary or friction ridges (colloquially known as fingerprints). Note that dermal papilla has two meanings referring to separate anatomical features. The dermal papilla of the dermal–epidermal junction should not be confused with the dermal papilla cells at the base of each hair follicle.

The pattern of ridges produced in hands and feet are only partly genetically determined features that are developed before birth, the timing and events around the ridge formation area also contributing.[5] They remain substantially unaltered (except in size) throughout life, and therefore determine the patterns of fingerprints, making them useful in certain functions of personal identification.[6]

The dermal papillae are part of the uppermost layer of the dermis, the papillary dermis, and the ridges they form greatly increase the surface area between the dermis and epidermis. Because the main function of the dermis is to support the epidermis, this greatly increases the exchange of oxygen, nutrients, and waste products between these two layers. Additionally, the increase in the surface area prevents the dermal and epidermal layers from separating by strengthening the junction between them. With age, the papillae tend to flatten and sometimes increase in number.[7]

The skin of the hands and fingers and the feet and toes is known by forensic scientists as friction ridge skin. It is known by anatomists as thick skin, volar skin or hairless skin. It has raised ridges, a thicker and more complex epidermis, increased sensory abilities, and the absence of hair and sebaceous glands. The ridges increase friction for improved grasping.[8]

In mucous membranes, the equivalent structures to dermal papillae are generally termed "connective tissue papillae", which interdigitate with the rete pegs of the superficial epithelium. Dermal papillae are less pronounced in thin skin areas.

Reticular dermis

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The reticular dermis is the lower layer of the dermis, found under the papillary dermis, composed of dense irregular connective tissue featuring densely-packed collagen fibers. It is the primary location of dermal elastic fibers.[2]

The reticular region is usually much thicker than the overlying papillary dermis. It receives its name from the dense concentration of collagenous, elastic, and reticular fibers that weave throughout it. These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Within the reticular region are the roots of the hair, sebaceous glands, sweat glands, receptors, nails, and blood vessels. The orientation of collagen fibers within the reticular dermis creates lines of tension called Langer's lines, which are of some relevance in surgery and wound healing.[9]

See also

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References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Dermis

View on Grokipedia
from Grokipedia
The dermis is the dense, fibrous layer of that forms the middle region of the skin, situated directly beneath the and above the subcutaneous hypodermis, providing essential , elasticity, and nourishment to the overlying epidermal cells. Composed primarily of an rich in (types I and III) and elastic fibers, along with such as glycosaminoglycans, the dermis originates from mesenchymal tissue and varies in thickness from approximately 1 to 4 mm across different body regions. Structurally, the dermis is divided into two main layers: the superficial papillary dermis, which consists of with fine and fibers arranged in a network that facilitates nutrient exchange and houses loops; and the deeper reticular dermis, comprising that forms the bulk of the layer and contains thicker bundles of for tensile strength. Key components embedded within the dermis include blood vessels and lymphatics for circulation, endings such as Meissner's and Pacinian corpuscles for touch and pressure detection, hair follicles, sebaceous and sweat glands, and immune cells like mast cells and histiocytes. The primary cellular resident, fibroblasts, synthesizes and maintains the , while adipocytes may appear in thinner regions. Functionally, the dermis plays a critical role in protecting deeper tissues from mechanical stress, aiding through vasoactive vessels and specialized glomus bodies that control dissipation, and enabling sensory perception via its network of mechanoreceptors and nociceptors. It also supports by providing a scaffold for epidermal regeneration and contributes to immune defense through resident leukocytes. These attributes make the dermis indispensable for integrity and overall , with disruptions often leading to conditions like dermal or .

Overview

Definition and location

The dermis is the middle layer of the skin, a structure that lies beneath the and provides essential mechanical support to the by anchoring the outer layer and contributing to overall skin resilience. Composed primarily of fibrous elements, it serves as the foundational framework for skin integrity, enabling the organ to withstand physical stresses. Anatomically, the dermis is positioned directly below the , to which it attaches via a , and above the subcutaneous hypodermis, forming a transitional zone that integrates the 's protective and supportive functions. Its thickness varies significantly across body regions, typically ranging from 0.5 mm to 4 mm, with the thinnest areas occurring on the eyelids (around 0.5 mm) and the thickest on the back (up to 4 mm); palms and soles are also relatively thick. These regional differences in dermal thickness correlate with the 's adaptive needs in areas exposed to varying levels of mechanical demand and environmental exposure. The term "dermis" originates from the New Latin form of the word derma, meaning "" or "hide," reflecting its role as the "true skin" beneath the surface layer.

General composition

The dermis is primarily composed of , featuring a sparse population of cells embedded within a robust (ECM). This arrangement provides structural support and flexibility to the . The ECM forms the predominant structural framework, comprising interwoven fibers and an amorphous that fills the intercellular spaces. In terms of volume, the ECM accounts for approximately 90% of the dermis, while cellular components represent about 10%, highlighting the acellular dominance that defines its mechanical properties. The within the ECM is rich in glycosaminoglycans (GAGs), which contribute to hydration and resilience, constituting 0.1–0.3% of the total skin weight with a higher concentration in the dermis compared to the . Additionally, the dermis houses essential vascular and neural elements, including blood vessels that supply nutrients and oxygen, lymphatic vessels that aid in , and that transmit sensory information. Skin appendages such as hair follicles and glands are also integrated within this matrix, contributing to its overall functionality without altering its core. The dermis consists of two main layers: the superficial papillary dermis, which is looser in structure, and the deeper reticular dermis, which is denser.

Anatomical layers

Papillary dermis

The papillary dermis is the uppermost layer of the dermis, situated immediately beneath the and forming the interface between the two primary strata. It consists of loose areolar , characterized by a network of fine fibers (primarily types I and III) and thinner elastic fibers, which contribute to its flexible and pliable nature. This layer typically measures 0.1 to 0.3 mm in thickness, accounting for approximately 10 to 20% of the total dermal volume, with variations depending on body region—thinner on areas like the eyelids and thicker on the palms. A defining feature of the papillary dermis is the presence of dermal papillae, which are finger-like projections of that extend upward into the overlying , interdigitating with the epidermal rete ridges. These papillae significantly increase the surface area of contact between the dermis and , enhancing mechanical and facilitating efficient nutrient and oxygen exchange. The high of this layer, marked by a dense network of within the papillae and a superficial subpapillary , supports its role in nourishing the avascular through from capillary loops. In contrast to the denser reticular dermis below, the papillary dermis's loose structure allows for greater permeability and metabolic activity at the epidermal junction, optimizing its supportive and nutritive functions.

Reticular dermis

The reticular dermis constitutes the deeper and thicker portion of the dermis, situated immediately below the papillary dermis and above the hypodermis. It accounts for approximately 80% of the total dermal volume and exhibits a thickness ranging from 1 to 3 mm, varying by anatomical location such as greater depth on the back compared to thinner regions like the eyelids. This layer is composed of , featuring coarse bundles of primarily type I and type III fibers arranged in a interwoven network that imparts significant mechanical strength and durability to the skin. Elastic fibers, including elaunin fibers, are interspersed among the , providing resilience, though they are less abundant relative to the dominant components. In contrast to the overlying papillary dermis, the reticular dermis lacks dermal papillae and instead incorporates larger vascular structures, such as vessels and nerves, along with glandular elements like sweat and sebaceous glands. The reticular dermis transitions gradually into the hypodermis through a progressive coarsening of its fibers, which extend without a sharp demarcation into the underlying subcutaneous . follicles and other skin appendages are anchored within this layer, enhancing overall dermal stability.

Cellular components

Fibroblasts and other resident cells

Fibroblasts represent the predominant in the dermis, serving as the primary architects of the skin's structural . These mesenchymal cells exhibit a characteristic spindle-shaped morphology with elongated cytoplasmic processes, enabling them to navigate and interact within the (ECM). Their core function involves the synthesis and maintenance of key ECM components, including fibers (predominantly types I and III), , and proteoglycans such as and biglycan, which collectively provide tensile strength, elasticity, and hydration to the dermal layer. A specialized variant of fibroblasts, known as myofibroblasts, emerges particularly during tissue repair processes. These cells acquire contractile properties through the expression of alpha-smooth muscle (α-SMA) and prominent actin-myosin filaments, allowing them to generate mechanical tension that facilitates wound closure and ECM remodeling. While quiescent fibroblasts maintain , myofibroblasts represent a transient, activated state induced by environmental cues like mechanical stress. Beyond fibroblasts, other resident cells contribute to dermal architecture. Adipocytes, though present in smaller numbers, are notably found in the upper papillary dermis, where they provide mechanical cushioning and support epidermal structures. Mast cells also reside within the dermis, embedded in the to help stabilize the local environment through their granular contents. Cell density varies by dermal layer, with the papillary dermis exhibiting a higher concentration of fibroblasts in a looser arrangement compared to the denser packing in the reticular dermis.

Immune cells

The dermis harbors a diverse of immune cells that form a resident network essential for local immune surveillance and response, distinct from epidermal components. Key resident immune cells include macrophages, dendritic cells, lymphocytes, and mast cells, which collectively contribute to both innate and adaptive immunity in the skin. These cells are replenished from precursors and maintain homeostasis while responding to threats such as pathogens or allergens. Macrophages, the most abundant hematopoietic cells in steady-state dermis, perform to clear debris and pathogens, and release such as IL-1β, TNF-α, and IL-6 to orchestrate and tissue repair. Dendritic cells, specialized antigen-presenting cells, capture and process antigens in the dermis, migrating to draining nodes to initiate adaptive immune responses by activating T cells; subsets like CD301b+ dendritic cells promote Th2-biased responses relevant to allergic contexts. Lymphocytes, primarily T cells including + and γδ subsets, mediate adaptive immunity through production (e.g., IFN-γ, IL-17) and direct , with γδ T cells providing rapid innate-like defense against infections. Mast cells, enriched near dermal appendages, degranulate to release and like TNF-α upon IgE cross-linking, amplifying immediate reactions. In terms of density and distribution, immune cells are more concentrated in the papillary dermis for enhanced surveillance of the skin surface, with macrophages and dendritic cells showing higher there compared to the reticular dermis, which supports broader leukocyte infiltration during responses. Overall, lymphocytes constitute approximately 40% of dermal immune cells, macrophages about 10%, dendritic cells around 15% within myeloid populations, and mast cells form a significant resident pool estimated at 7,000 per gram of dermis tissue in normal , increasing with age. This layered distribution facilitates rapid detection in superficial layers while allowing escalation in deeper tissues. These cells contribute to dermal by recruiting and activating additional leukocytes through gradients and signaling, with macrophages and dendritic cells driving pro-inflammatory cascades. In allergic responses, mast cells play a central in conditions like urticaria, where IgE-mediated triggers release, leading to and wheal formation, often in concert with infiltration. Interaction with the dermal vasculature is crucial for immune function, as perivascular macrophages and mast cells regulate at post-capillary venules by secreting and growth factors like VEGF, facilitating recruitment of circulating monocytes, neutrophils, and T cells during . Dendritic cells and mast cells further enhance this by forming synapses that transfer antigens and signals, promoting coordinated responses.

Extracellular matrix

Collagen fibers

Collagen fibers constitute the predominant component of the dermal extracellular matrix, comprising approximately 70-80% of its dry weight and providing essential structural integrity to the skin. In the human dermis, type I collagen is the most abundant, accounting for 80-90% of total collagen content, and forms thick fibrils that confer high tensile strength to withstand mechanical stresses. Type III collagen, making up about 5-15%, consists of thinner fibrils primarily located in the papillary dermis, contributing to tissue flexibility and early wound healing responses. These two types together form a hierarchical network of fibers that interweave with elastin to enable skin recoil after deformation. Structurally, collagen molecules are composed of three polypeptide chains arranged in a triple-helix configuration, which self-assemble extracellularly into with diameters ranging from 50 to 200 nm. These are further stabilized by enzymatic cross-links formed through the action of lysyl , an that oxidizes residues to create covalent bonds, enhancing fibril rigidity and resistance to degradation. Dermal fibroblasts are the primary cells responsible for collagen synthesis, producing procollagen precursors that are processed and assembled outside the cell. This process is tightly regulated by transforming growth factor-β (TGF-β) signaling, which upregulates gene expression and promotes fibril assembly in response to mechanical or injury-related cues. Biomechanically, fibers in the dermis exhibit a of approximately 1-10 MPa, reflecting their role in balancing tensile strength and elasticity to accommodate stretching and deformation without rupture.

Elastin and ground substance

constitutes 2–4% of the (ECM) in the adult human dermis, forming an intricate network of amorphous elastic fibers that provide resilience to the skin. These fibers are primarily composed of tropoelastin, a soluble precursor protein that undergoes cross-linking via lysyl oxidase-mediated desmosine bonds to create insoluble, highly elastic structures organized into fibers and lamellae. This architecture enables the dermis to undergo substantial deformation, with fibers supporting stretch and recoil capabilities of up to 100% or more, allowing full recovery without permanent deformation. In the dermis, is more abundant in the deeper reticular layer, where it forms a three-dimensional meshwork oriented both parallel and perpendicular to the skin surface, contributing to overall tissue flexibility. Its distribution decreases with age, as elastin synthesis by fibroblasts diminishes after , leading to fragmentation and reduced elasticity over time due to limited turnover and . The of the dermal ECM, an amorphous gel-like medium, is primarily composed of glycosaminoglycans () such as and , along with proteoglycans and glycoproteins, which fill the spaces between elastic and other fibers. , a key nonsulfated , exhibits exceptional hydrophilic properties, capable of binding up to 1,000 times its weight in to maintain dermal hydration and turgor. Proteoglycans, such as and biglycan, further enhance this by forming complexes that regulate retention and molecular interactions within the ECM. Functionally, the facilitates the of nutrients, ions, and metabolites through the avascular dermis by providing a hydrated, low-viscosity environment that supports solute transport and tissue . fibers integrate with the surrounding and other ECM components to confer viscoelastic properties to the dermis, where the of balances hydration-mediated for dynamic movement.

Functions

Structural support

The dermis serves as the primary structural foundation of the skin, conferring mechanical integrity through its dense network of extracellular matrix components, particularly collagen and elastin fibers. This framework enables the skin to withstand everyday physical stresses without compromising its barrier function. Tensile strength is predominantly provided by the collagen network, which forms a robust scaffold of type I and type III fibers that resists tearing and deformation under mechanical load. In the reticular dermis, these densely packed collagen fibrils align and reorganize in response to tension, blunting stress concentrations and preventing crack propagation, as observed in studies of skin's tear resistance mechanisms. This property is essential for maintaining skin cohesion during activities involving stretching or impact. Elasticity arises from elastin fibers, which constitute 2–4% of the dermis's dry mass and form a three-dimensional meshwork that allows for reversible deformation and rapid recoil. Elastin operates at low strains with a of 0.1–1.5 MPa, enabling the skin to stretch during movement—such as joint flexion—and return to its original shape, complementing collagen's higher-modulus resistance at greater loads. The dermis anchors the via the dermal-epidermal junction, a corrugated interface featuring rete ridges and dermal papillae that enhance adhesion through hemidesmosomes and proteins like collagen IV and . This anchorage resists shear forces, particularly in high-friction areas like palms and soles, where deepened ridges increase mechanical interlock and prevent . Similarly, the dermis embeds and supports such as hair follicles and glands, securing them against displacement from external forces. Overall, these mechanical attributes contribute to the skin's barrier against trauma by distributing forces across the tissue, protecting underlying structures from abrasion, puncture, and excessive strain. The extracellular matrix's composition, including and , underpins this resilience without delving into its detailed components.

Sensory and vascular roles

The dermis plays a crucial role in sensory through its extensive innervation by somatosensory . Free nerve endings, primarily associated with Aδ and C fibers, are distributed throughout the dermis and detect , changes, and crude touch stimuli. These unmyelinated or thinly myelinated endings respond to mechanical , variations, and noxious stimuli, transmitting signals to the for protective reflexes and awareness. Encapsulated mechanoreceptors further enhance tactile discrimination within specific dermal layers. Meissner corpuscles, located in the papillary dermis beneath the epidermal ridges of glabrous skin such as the fingers, palms, and soles, serve as rapidly adapting receptors for low-frequency and light touch, enabling fine discrimination of textures and object manipulation. In contrast, Pacinian corpuscles reside deeper in the reticular dermis and , functioning as rapidly adapting sensors for high-frequency (around 200-300 Hz) and deep pressure, with their onion-like filtering rapid mechanical deformations to detect subtle movements like those from machinery or impacts. The vascular network of the dermis ensures vital nutrient and oxygen delivery to the overlying avascular while supporting dermal . In the papillary dermis, arterioles (10-100 μm in diameter) give rise to capillary loops that ascend into the dermal papillae and drain into postcapillary venules (10-200 μm), forming a superficial horizontal at the epidermal-dermal junction. This arrangement allows for efficient of oxygen and nutrients across the thin epidermal barrier (0.06-0.6 mm thick), with densities ranging from 16-65 per mm² to meet metabolic demands without excessive vascularization. Deeper in the reticular dermis, a more robust horizontal of larger arterioles and venules supplies the bulkier , follicles, and glands, facilitating waste removal and maintaining tissue viability over the dermis's 1-4 mm thickness. Beyond basic , the dermal vasculature contributes to through specialized structures. Arteriovenous anastomoses, direct connections between arterioles and venules bypassing the bed, are concentrated in acral regions like the hands and feet; their dilation, mediated by reduced sympathetic tone from the , increases cutaneous blood flow up to 8 L/min, promoting radiative and convective heat loss that accounts for about 60% of total body heat dissipation. The dermis also supports eccrine sweat glands embedded within its layers, which, upon activation, secrete hypotonic fluid for evaporative cooling (contributing ~22% of heat loss), with vascular plexuses providing the necessary hydration and nutrients to sustain glandular function during prolonged . Lymphatic vessels in the dermis maintain and immune surveillance by draining interstitial fluid and facilitating cellular transport. Initial lymphatic capillaries, blind-ended and highly permeable, originate in the papillary dermis and collect excess interstitial fluid (~3 L/day) that escapes the vascular system, propelling it unidirectionally via intrinsic contractions and extrinsic compression toward collecting vessels in the reticular dermis. These lymphatics also transport immune cells, such as dendritic cells and lymphocytes, from peripheral tissues to draining lymph nodes, enabling and adaptive immune responses while preventing accumulation.

Development and maintenance

Embryonic development

The dermis arises primarily from mesodermal tissues during early embryogenesis, with contributions from the forming the dermis in the limbs and ventral regions, paraxial mesoderm contributing to the dorsal and trunk dermis, and cells supplying the craniofacial dermis. These mesenchymal precursors undergo epithelial-to-mesenchymal transition and migrate to underlie the developing , establishing the foundational layer. Histological distinction of the dermis emerges as early as the sixth week of embryonic development, coinciding with the initial migration of s into the subepidermal space. By the eighth week, fibroblast proliferation intensifies, accompanied by the onset of (ECM) deposition, including early and synthesis that provides initial structural support. This timeline aligns with the broader phase, where the dermis transitions from a loose mesenchymal aggregate to a more organized tissue. Differentiation into papillary and reticular layers begins in the embryonic period, with the papillary dermis forming first from the subjacent through localized condensation and fine network assembly. The reticular dermis develops subsequently, driven by progressive accumulation of thicker bundles produced by maturing s, establishing the denser framework observed later in fetal stages. Epidermal-dermal interactions are crucial for dermal patterning, mediated by inductive signals from the overlying that promote mesenchymal and ECM organization. Key pathways include Wnt signaling, which orchestrates reciprocal communication to specify dermal cell fates, and BMP signaling, which regulates differentiation and deposition in response to epidermal cues. These molecular exchanges ensure coordinated development, preventing disorganized tissue formation.

Postnatal changes and repair

After birth, the dermis undergoes adaptive changes influenced by hormonal fluctuations. Estrogen plays a key role in maintaining dermal hydration by stimulating hyaluronic acid synthesis, which enhances water retention and supports skin elasticity. In contrast, androgens contribute to increased dermal thickness, particularly evident in gender-specific differences that emerge post-puberty, where higher androgen levels promote collagen deposition and overall dermal density. These hormonal effects help transition the dermis from its embryonic state to a mature structure capable of responding to environmental stresses. With advancing age, the dermal experiences progressive degradation, leading to structural weakening. Collagen production declines by approximately 1% annually after the mid-20s, resulting in net loss and fragmentation of , which reduces firmness and contributes to formation. fibers also degrade over time due to enzymatic breakdown and oxidative damage, diminishing the dermis's recoil properties and exacerbating sagging. These changes are driven by downregulated transforming growth factor-β signaling and elevated matrix metalloproteinases, altering the dermal microenvironment to impair mechanical integrity. Dermal repair, particularly through , occurs in overlapping phases that restore tissue integrity. The inflammatory phase, lasting several days, involves immune cell influx—primarily neutrophils and macrophages—for debris clearance and defense, mediated by platelet-derived growth factors and cytokines. This transitions to the proliferative phase over weeks, where fibroblasts synthesize components like and glycosaminoglycans, while forms new vessels to support . Myofibroblasts, differentiated from fibroblasts, drive wound contraction through actin-mediated traction on the matrix. In the remodeling phase, spanning months, collagen cross-links strengthen the scar, though tensile strength reaches only about 80% of uninjured dermis. Excessive activity, however, can lead to , characterized by overproduction of disorganized and persistent contraction. Hormonal modulation influences these processes, with enhancing overall healing efficiency by promoting and reducing .

Clinical significance

Common disorders

The dermis, the supportive layer beneath the epidermis, is implicated in various genetic disorders that compromise its structural integrity. Ehlers-Danlos syndrome (EDS) encompasses a group of heritable disorders primarily arising from defects in synthesis or structure, leading to dermal fragility, hyperextensible skin, and impaired . These abnormalities weaken the of the dermis, resulting in easy bruising, atrophic scarring, and increased susceptibility to trauma. represents another genetic condition characterized by elastin deficiency or disruptions in assembly within the dermis, manifesting as loose, sagging, and inelastic skin that hangs in folds. This elastin shortfall reduces the dermis's recoil properties, often leading to premature aging-like appearance and potential internal organ involvement. Inflammatory disorders frequently target the dermis through immune dysregulation, altering its barrier and inflammatory responses. Atopic dermatitis, a chronic immune-mediated condition, disrupts the dermal-epidermal barrier via T-cell driven , causing dermal , pruritus, and lichenification in chronic cases. This leads to impaired dermal hydration and increased allergen penetration, perpetuating a cycle of . , another immune-mediated dermatosis, involves dermal infiltration by neutrophils, T lymphocytes, and macrophages, resulting in papillary dermal and spongiform pustules that extend into the dermis. These changes manifest as erythematous plaques with scaling, driven by release such as IL-17 and IL-23 from dermal immune cells. Infectious processes can invade the dermis, leading to acute or chronic pathology. Cellulitis is an acute bacterial infection, typically by or species, that spreads through the deep dermis and , causing , warmth, and swelling due to bacterial proliferation and host inflammatory response. , caused by , induces perineural granulomatous inflammation in the dermis, damaging small dermal nerves and leading to , hypopigmented patches, and eventual dermal . This nerve involvement in the dermis contributes to trophic ulcers and deformities over time. Globally, inflammatory dermal disorders like affect 10-20% of children and up to 3% of adults, highlighting their significant burden. Genetic conditions such as EDS and are rarer, with incidences around 1 in 5,000 and 1 in 1,000,000, respectively, underscoring the spectrum from common to exceptional dermal pathologies.

Aging and pathology

As individuals age, the dermis undergoes progressive structural alterations that compromise its integrity. Collagen content diminishes by approximately 1% annually after the mid-20s, leading to reduced dermal thickness and elasticity. fibers fragment and degrade, resulting in diminished and sagging. Additionally, glycosaminoglycans (GAGs) decrease, impairing retention and contributing to dryness. Functional declines in the aging dermis further exacerbate these changes. is impaired due to slower and reduced vascularization, prolonging recovery times. Sensory diminishes as endings in the dermis decrease, leading to reduced tactile sensitivity. Vascular fragility increases, making dermal blood vessels more prone to rupture and bruising. Photoaging, driven by chronic ultraviolet (UV) exposure, accelerates dermal pathology through upregulation of matrix metalloproteinases (MMPs), which degrade the (ECM). This UV-induced ECM breakdown not only intensifies wrinkling and laxity but also heightens the risk of skin cancers, such as , by promoting mutagenic inflammation. Gender-specific differences emerge post-menopause, when decline accelerates dermal thinning in women, with reaching up to 2% per year and overall thickness reducing by about 1.13% annually.

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