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Dermis of skin

The dermis is the middle layer of the skin, located between the epidermis and the subcutaneous tissue (hypodermis). It forms the connective tissue framework that supports and nourishes the epidermis and houses vital structures such as blood vessels, nerves, sweat glands, sebaceous glands, hair follicles, and lymphatics.

Composed primarily of collagen and elastic fibers, the dermis provides strength, elasticity, and thermoregulation. It plays a key role in wound healing, immune defense, and sensory perception. The dermis varies in thickness across the body — thinnest on the eyelids (~0.3 mm) and thickest on the palms and soles (~3 mm).

Synonyms

  • Corium

  • True skin

  • Cutis

Layers and Structure

The dermis is divided into two histological layers with distinct structural and functional characteristics:

  • Papillary Layer:

    • The superficial thin layer directly beneath the epidermis.

    • Composed of loose connective tissue, fine collagen (type I and III), and abundant capillaries.

    • Contains dermal papillae, which interdigitate with epidermal ridges to strengthen the dermo-epidermal junction.

    • Rich in sensory nerve endings and immune cells.

  • Reticular Layer:

    • The deeper, thicker layer of dense irregular connective tissue.

    • Contains thick bundles of collagen (type I) and elastic fibers, giving the skin tensile strength.

    • Houses hair follicles, sweat glands, sebaceous glands, and blood vessels.

    • Provides structural support and resilience.

Components

  • Fibrous matrix: Collagen, elastin, and reticular fibers

  • Ground substance: Proteoglycans, glycosaminoglycans (mainly hyaluronic acid)

  • Cells: Fibroblasts, macrophages, mast cells, lymphocytes, and dermal dendritic cells

  • Vessels and nerves: Extensive capillary networks, lymphatics, and sensory nerve endings (Meissner’s corpuscles, Ruffini endings, Pacinian corpuscles)

Relations

  • Superficially: Epidermis, connected by the dermo-epidermal junction

  • Deeply: Subcutaneous (hypodermal) tissue containing fat and larger vessels

  • Laterally: Continuous with adjacent dermal regions forming skin folds and creases

Nerve Supply

  • Sensory innervation: Cutaneous branches of spinal nerves (free nerve endings, Merkel cells, Meissner’s and Pacinian corpuscles)

  • Autonomic fibers: Sympathetic fibers regulate sweat glands, blood vessels, and piloerection

Function

  • Mechanical strength: Collagen and elastin provide tensile resistance and elasticity

  • Thermoregulation: Rich vascular network aids heat dissipation and conservation

  • Sensation: Contains receptors for touch, pain, temperature, and pressure

  • Protection: Absorbs mechanical stresses, shields deeper tissues from trauma

  • Immune defense: Houses resident immune cells involved in inflammatory responses

  • Wound healing: Fibroblast proliferation and collagen deposition repair skin integrity

  • Nutrient support: Capillaries nourish the avascular epidermis

Clinical Significance

  • Dermatitis: Inflammation of the dermis (allergic, irritant, or infectious causes)

  • Scarring and fibrosis: Excessive collagen deposition during wound healing

  • Aging: Loss of collagen and elastin leads to wrinkles and reduced elasticity

  • Infections: Cellulitis, abscesses, and bacterial spread within dermal layers

  • Burns: Second-degree (partial-thickness) burns involve dermis; third-degree burns destroy it completely

  • Tumors: Origin site for basal cell carcinoma, melanoma invasion, and soft-tissue neoplasms

  • Imaging role: Dermal thickness and signal help evaluate edema, inflammation, tumors, and trauma

MRI Appearance

  • T1-weighted images:

    • Normal dermis: Intermediate-to-low signal intensity (denser collagen content)

    • Subcutaneous fat: Bright, providing contrast with darker dermis

    • Pathology: Edema or inflammation appears as subtle intermediate-to-bright thickening

  • T2-weighted images:

    • Normal dermis: Intermediate signal intensity, slightly darker than on T1 due to collagen density

    • Edematous or inflamed dermis: Bright hyperintense signal with loss of dermal–fat interface

    • Fibrosis: Low signal from collagen deposition

  • STIR:

    • Normal dermis: Intermediate-to-dark signal

    • Inflammation, cellulitis, or edema: Bright hyperintense signal spreading through dermis and subcutis

    • Sensitive for early soft-tissue infection or inflammatory changes

  • Proton Density Fat-Saturated (PD FS):

    • Normal dermis: Intermediate-to-dark signal with sharp interface from fat

    • Pathology: Bright signal indicates dermal edema, inflammatory infiltration, or neoplastic invasion

  • T1 Fat-Sat Post-Contrast:

    • Normal dermis: Uniform mild enhancement due to vascularity

    • Inflammation: Diffuse or band-like enhancement pattern

    • Infection: Intense enhancement with dermal thickening and blurred margins

    • Neoplasm: Heterogeneous enhancement depending on tumor vascularity

CT Appearance

Non-Contrast CT:

  • Dermis: Intermediate soft-tissue density layer between bright subcutaneous fat and low-density epidermis

  • Normal thickness: ~1–3 mm depending on site

  • Pathology:

    • Dermal thickening in cellulitis or edema

    • Loss of normal skin stratification in inflammation or infiltration

    • Soft-tissue calcifications in scleroderma or chronic inflammation

Post-Contrast CT (standard):

  • Normal dermis: Mild, uniform enhancement due to vascular plexus

  • Inflammation: Diffuse dermal enhancement with subcutaneous fat stranding

  • Infection: Irregular or nodular enhancement in cellulitis, abscess, or neoplastic spread

  • Chronic fibrosis: Poorly enhancing low-density dermal thickening

MRI images

Dermis of skin of skin of foot axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000