Skin Anatomy

The skin is not merely a protective covering—it is a complex, multifunctional organ essential for survival, homeostasis, and clinical diagnosis. For medical students and healthcare professionals, a solid understanding of skin anatomy is critical, as many systemic diseases manifest first through cutaneous changes.

Overview of the Skin Layers

The skin is the largest and heaviest single organ of the human body, accounting for approximately 16% of total body weight. It covers an estimated surface area of 1.2 to 2.3 m², depending on body size and age.

Anatomically, the skin is composed of three distinct layers:

1. Epidermis
2. Dermis
3. Subcutaneous tissue (Hypodermis)

Each skin layer has specialized structures and functions that contribute to protection, sensation, thermoregulation, and metabolism.

1. Epidermis

The epidermis is the most superficial layer of the skin. It is a thin, avascular, keratinized stratified squamous epithelium, meaning it contains no blood vessels and relies entirely on the underlying dermis for nutrition.

Structural Layers of the Epidermis

The epidermis consists of two main functional components:

▪ Stratum Corneum (Outer Layer)

• Composed of dead, flattened, keratinized cells
• Acts as a protective barrier against mechanical injury, pathogens, and water loss

▪ Malpighian Layer (Inner Cellular Layer)

This layer includes:

• Stratum basale
• Stratum spinosum

Key functions:

• Keratin production (by keratinocytes)
• Melanin synthesis (by melanocytes)

Cell migration from the basal layer to the stratum corneum takes approximately one month, a clinically relevant fact when considering wound healing, psoriasis, and drug effects on skin turnover.

2. Dermis

Beneath the epidermis lies the dermis, a thick, vascularized connective tissue layer that provides strength, elasticity, and nourishment to the epidermis.

Composition of the Dermis

The dermis is composed of:

• Dense collagen fibers (tensile strength)
• Elastic fibers (skin elasticity)
• Ground substance

Structures Found in the Dermis

• Sebaceous glands
• Sweat glands (eccrine and apocrine)
• Hair follicles
• Blood vessels
• Lymphatics
• Most cutaneous nerve endings

Because of its rich innervation, the dermis is responsible for pain, temperature, pressure, and touch sensation.

Dermal Structures and Their Functions

Structure	Location in Dermis	Function	Clinical Significance
Sebaceous glands	Upper dermis	Sebum secretion	Acne vulgaris
Sweat glands (Eccrine)	Deep dermis	Thermoregulation	Heat intolerance disorders
Sweat glands (Apocrine)	Deep dermis	Scent secretion	Hidradenitis suppurativa
Hair follicles	Entire dermis	Hair production	Alopecia, folliculitis
Cutaneous nerves	Throughout dermis	Sensory perception	Neuropathic pain

3. Subcutaneous Tissue (Hypodermis)

Inferior to the dermis is the subcutaneous tissue, primarily composed of adipose (fat) tissue.

Functions of the Subcutaneous Layer

• Thermal insulation
• Energy storage
• Shock absorption
• Anchoring the skin to underlying structures

This layer also serves as an important site for subcutaneous injections and plays a role in drug absorption.

Skin Layers	Location	Main Components	Vascular Supply	Primary Functions	Clinical Relevance
Epidermis	Outermost layer	Keratinocytes, melanocytes, Langerhans cells	Avascular	Barrier protection, keratinization, pigmentation	Site of psoriasis, eczema, superficial burns
Dermis	Beneath epidermis	Collagen, elastic fibers, glands, hair follicles, nerves	Highly vascular	Strength, elasticity, sensation, thermoregulation	Involved in scarring, aging, inflammatory diseases
Subcutaneous Tissue (Hypodermis)	Deepest layer	Adipose tissue, connective tissue	Vascular	Insulation, energy storage, cushioning	Injection site, lipodystrophy, metabolic relevance

Skin Color and Pigmentation

Normal skin color is not determined by a single factor. It results from the interaction of pigments, blood flow, and tissue optics.

Major Determinants of Skin Color

1. Melanin

• A brownish pigment produced by melanocytes
• Genetically determined
• Increased by ultraviolet (UV) exposure
• Primary determinant of racial and individual skin color differences

2. Hemoglobin

• Oxyhemoglobin: bright red, found in arteries and capillaries → causes skin redness
• Deoxyhemoglobin: darker, bluish, found in veins
• Light scattering through skin layers makes veins appear bluer than they actually are

3. Carotene

• Yellow pigment
• Stored in subcutaneous fat
• Prominent in palms and soles
• Excess can cause carotenemia (yellowish skin without scleral icterus)

4. Bilirubin

• Yellow-brown pigment
• Derived from heme breakdown
• Elevated levels cause jaundice, a critical clinical sign of liver or hematologic disease.

Pigment	Color	Source	Primary Location	Clinical Relevance
Melanin	Brown to black	Melanocytes	Epidermis	Albinism, vitiligo, melanoma
Oxyhemoglobin	Bright red	Oxygenated blood	Capillaries	Erythema, inflammation
Deoxyhemoglobin	Bluish	Venous blood	Veins	Cyanosis
Carotene	Yellow	Diet-derived	Subcutaneous fat	Carotenemia
Bilirubin	Yellow-brown	Heme breakdown	Blood and tissues	Jaundice

Clinical Relevance of Skin Anatomy

Understanding skin anatomy is essential for:

• Diagnosing dermatologic and systemic diseases
• Interpreting skin color changes (cyanosis, pallor, jaundice)
• Performing procedures (biopsies, injections, suturing)
• Understanding wound healing and scarring
• Assessing burns and pressure injuries

Ignoring anatomical depth and structure leads to poor clinical judgment—something no healthcare professional can afford.

Skin Layers and Burn Depth Correlation

Burn Degree	Skin Layers Involved	Typical Features	Healing Pattern
First-degree	Epidermis only	Erythema, pain	Heals without scarring
Second-degree	Epidermis + dermis	Blisters, severe pain	Possible scarring
Third-degree	All skin layers	Painless, pale or charred	Requires grafting

References & More

1. Yousef H, Alhajj M, Fakoya AO, et al. Anatomy, Skin (Integument), Epidermis. [Updated 2024 Jun 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: Pubmed
2. Yousef H, Alhajj M, Fakoya AO, Sharma S. Anatomy, Skin (Integument), Epidermis. 2024 Jun 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 29262154. Pubmed
3. Bickley, L. S., Szilagyi, P. G., Hoffman, R. M., & Soriano, R. P. (2021). Bates’ guide to physical examination and history taking, 12e.