Clinical meaning
The integumentary system is the body's largest organ, accounting for approximately 16% of total body weight, and serves as the primary interface between the internal body and the external environment. A comprehensive dermatological assessment is a fundamental nursing skill that enables early identification of skin disorders, systemic disease manifestations, malignancies, pressure injuries, wound healing complications, and medication adverse effects. Understanding skin anatomy, lesion morphology, and systematic assessment techniques is essential for accurate documentation, appropriate intervention, and effective communication with the healthcare team. The skin consists of three primary layers. The epidermis is the outermost avascular layer composed of stratified squamous keratinized epithelium. Its primary functions include barrier protection against pathogens, chemicals, UV radiation, and mechanical injury, as well as prevention of transepidermal water loss (TEWL). The epidermis is organized into five strata (from deepest to most superficial): stratum basale (germinativum -- single layer of stem cells and melanocytes; active mitotic layer that regenerates the epidermis every 28-45 days), stratum spinosum (multiple layers of keratinocytes connected by desmosomes; contains Langerhans cells that serve as antigen-presenting immune sentinels), stratum granulosum (keratohyalin granules and lamellar bodies that form the lipid barrier), stratum lucidum (only in thick skin of palms and soles), and stratum corneum (15-20 layers of dead, flattened, keratin-filled cells called corneocytes embedded in a lipid matrix -- the primary physical barrier). Melanocytes in the stratum basale produce melanin (eumelanin and pheomelanin) that protects against UV-induced DNA damage; melanin content varies across populations and determines skin color. The dermis is the thick, vascularized connective tissue layer beneath the epidermis that provides structural support, elasticity, and nourishment. It contains collagen fibers (type I and III -- provide tensile strength), elastic fibers (provide elasticity and recoil), ground substance (glycosaminoglycans, proteoglycans -- provide hydration and cushioning), blood vessels (arterioles, capillaries, venules organized in superficial and deep plexuses -- regulate thermoregulation, wound healing, and inflammation), lymphatic vessels (immune surveillance and fluid drainage), nerve fibers and sensory receptors (free nerve endings for pain and temperature, Meissner corpuscles for light touch, Pacinian corpuscles for deep pressure and vibration, Ruffini endings for sustained pressure), hair follicles, sebaceous glands (produce sebum for skin lubrication), and eccrine and apocrine sweat glands (thermoregulation and excretion). The hypodermis (subcutaneous tissue) is the deepest layer composed of adipose tissue and loose connective tissue that provides insulation, energy storage, shock absorption, and anchoring of the skin to underlying structures. Primary skin lesions are those that arise de novo (not from modification of another lesion): macule (flat, circumscribed color change <1 cm -- freckle, petechiae), patch (flat color change >1 cm -- vitiligo, cafe-au-lait spot), papule (elevated, solid, <1 cm -- wart, insect bite), plaque (elevated, flat-topped, >1 cm -- psoriasis), nodule (solid, palpable, extends into dermis, 1-2 cm -- lipoma, erythema nodosum), tumor (solid, >2 cm -- large lipoma, dermatofibrosarcoma), vesicle (fluid-filled, <1 cm -- herpes simplex, contact dermatitis), bulla (fluid-filled, >1 cm -- bullous pemphigoid, burn blister), pustule (pus-filled -- acne, folliculitis), wheal (transient, edematous, irregular -- urticaria/hives from histamine release), and cyst (sac-containing fluid or semisolid material -- epidermal inclusion cyst, ganglion). Secondary skin lesions result from modification of primary lesions: scale (flaking keratin -- psoriasis, seborrheic dermatitis), crust (dried exudate -- impetigo), erosion (superficial loss of epidermis -- ruptured vesicle), ulcer (full-thickness loss extending through epidermis into dermis or deeper -- pressure injury, venous ulcer, arterial ulcer), fissure (linear crack extending into dermis -- athlete's foot, eczema), excoriation (superficial abrasion from scratching), lichenification (thickened skin with accentuated skin markings from chronic rubbing/scratching -- chronic eczema), atrophy (thinning of skin -- chronic corticosteroid use), scar (fibrous tissue replacing normal tissue after injury), and keloid (hypertrophic scar extending beyond the original wound margins -- more common in individuals of African, Asian, and Hispanic descent). Wound and pressure injury assessment is a critical nursing responsibility. The Braden Scale is the most widely used validated tool for pressure injury risk assessment, consisting of six subscales: sensory perception (ability to respond to pressure-related discomfort), moisture (degree of skin exposure to moisture), activity (degree of physical activity), mobility (ability to change and control body position), nutrition (usual food intake pattern), and friction/shear (degree of sliding against surfaces). Scores range from 6-23; lower scores indicate higher risk (15-18 = mild risk, 13-14 = moderate risk, 10-12 = high risk, 9 or below = very high risk). Pressure injury staging follows the NPUAP/NPIAP system: Stage 1 (intact skin with non-blanchable erythema -- place dorsum of hand on the area to check for warmth; dark-skinned patients may not show visible redness but may show color changes, warmth, or induration), Stage 2 (partial-thickness loss of dermis -- shallow open ulcer with pink wound bed or intact/ruptured serum-filled blister; does NOT include slough or bruising), Stage 3 (full-thickness tissue loss -- subcutaneous fat may be visible; bone, tendon, and muscle are NOT exposed), Stage 4 (full-thickness tissue loss with exposed bone, tendon, cartilage, or muscle), Unstageable (full-thickness loss obscured by slough or eschar -- cannot stage until debrided), and Deep Tissue Pressure Injury (DTPI -- intact or non-intact skin with localized area of persistent non-blanchable deep red, maroon, or purple discoloration; indicates damage to underlying tissue from pressure/shear). The nursing assessment must include systematic documentation using the ABCDE of skin lesion evaluation: Asymmetry, Border irregularity, Color variation, Diameter >6 mm, and Evolving characteristics -- this mnemonic is critical for melanoma screening and patient education about when to seek dermatological evaluation for concerning moles.