Fundamentals of Nursing · Skin Integrity
Structures and Function of the Skin
On this page 9 sections
In 30 seconds
The skin is the largest organ of the human body. It keeps water in and microbes out, senses the world, regulates body temperature, manufactures vitamin D, and helps the immune system raise an alarm. Because nurses see and touch the skin on every patient, every shift, it is the one organ system that is always part of the physical assessment — and often the first place disease or injury shows up.
Understanding the skin starts with its layers. From outside in: the Epidermis Outermost layer; tough, waterproof barrier of mostly dead keratin-filled cells Full entry → (thin, protective outer layer), the Dermis Middle layer with blood vessels, nerves, glands, hair follicles Full entry → (thicker middle layer with blood vessels, nerves, glands, and hair roots), and the hypodermis, or subcutaneous layer (fat and connective tissue that insulates and cushions). Attached to these are the skin's "accessories" — hair, nails, and two families of glands.
For nursing, the payoff is practical. Every assessment question — Is this redness normal or early pressure damage? Is this wound deep or shallow? Why does this patient's skin break down so easily? — is really a question about which layer is involved and what that layer needs to stay healthy. This topic builds the foundation for the rest of Chapter 24: Skin Integrity, Wound Classification, and Wound Healing.
Why this matters
The skin is the body's first line of defense, and when it breaks down, everything else is at risk. An intact barrier keeps bacteria, viruses, and fungi out; a break is an open door for infection. The skin also regulates fluid loss — widespread damage (as in major burns) causes dangerous dehydration and temperature instability, which is why burn patients need intensive monitoring (an advanced topic in later courses).
Skin is also a window into the rest of the body: jaundice shows in the skin and sclera before lab values confirm it; dehydration shows in skin Turgor How quickly skin returns to place when pinched Full entry →; poor circulation shows in color and temperature; early pressure injury shows as persistent redness. Medications are absorbed through the skin (transdermal patches), and many skin changes are treatment side effects. Finally, skin assessment is central to preventing pressure injuries — one of the most common, costly, and preventable harms in health care. You cannot prevent what you cannot see.
The college version
Core Concepts
The epidermis: the barrier
The epidermis is the outermost layer — what you see and touch. It has no blood vessels of its own; it is fed by diffusion from the dermis below. Its deepest cells constantly divide, and as new cells are pushed upward they fill with a tough protein called Keratin Tough protein that fills skin, hair, and nail cells Full entry →, flatten, and die. By the surface they are flat, dead, keratin-filled plates forming a waterproof, wear-resistant shield that is constantly shed and replaced.
Two other epidermal residents matter in nursing:
- Melanocytes produce Melanin Pigment from melanocytes that colors skin and absorbs UV Full entry →, the pigment that colors skin and absorbs UV radiation (tanning is a protective response, not a sign of health). Skin-color differences are clinically important: redness (Erythema Redness from increased blood flow Full entry →), pallor, and jaundice look different on different skin tones, so nurses assess color change against the person's baseline — checking mucous membranes, nail beds, and sclera, and asking the patient about their normal color.
- Immune sentinel cells (Langerhans cells) recognize invading microbes and trigger the immune response — the skin is part of the immune system, not just a wrapper.
The dermis: the workhorse
Beneath the epidermis lies the dermis — thicker connective tissue (collagen and elastin) that gives skin strength and stretch. It holds the real machinery:
- Blood vessels that feed the epidermis, regulate heat loss (dilating to release heat, constricting to conserve it), and bring immune cells to injuries.
- Nerve endings that detect touch, pressure, pain, and temperature — the skin as a sense organ.
- Hair follicles, each with a tiny muscle (arrector pili) that causes "goosebumps."
- Glands: sebaceous (oil) glands secrete Sebum Oil from sebaceous glands that conditions and waterproofs skin and hair Full entry →, which waterproofs and conditions skin and hair; sudoriferous (sweat) glands — eccrine glands (most of the body; cool by evaporation) and apocrine glands (armpits/groin; active after puberty).
When a wound reaches the dermis, it hurts (nerves), bleeds (vessels), and scars differently than a scrape that only grazes the epidermis — the basis of wound depth classification in Wound Classification.
The hypodermis: cushion and fuel
The deepest layer is mostly fat cells plus connective tissue. It insulates against cold, cushions underlying structures, stores energy, and anchors skin to deeper structures. Two nursing reasons this matters: subcutaneous tissue is where subcutaneous injections are given (needle depth and angle are designed to deposit medication here, not in dermis or muscle), and loss of subcutaneous fat (older adults, malnutrition, chronic illness) leaves bony prominences with less padding — one reason pressure injuries develop more easily.
Hair and nails
Hair grows from dermal follicles and is mostly dead keratin by the time it emerges; the arrector pili muscle makes it stand up ("goosebumps"). Nails are hardened keratin plates protecting fingertips and toes. Their color, thickness, and growth reflect circulation, nutrition, and oxygenation — nail-bed pallor or duskiness are assessment findings nurses look for.
Four headline functions
- Protection — physical barrier against microbes, chemicals, UV, and mechanical injury, backed by immune cells.
- Thermoregulation The body's temperature control Full entry → — sweat evaporation cools; vessel dilation/constriction moves heat; subcutaneous fat insulates.
- Sensation — nerve endings report touch, pressure, pain, and temperature, telling the body to pull off a hot stove or shift off a sore spot.
- Synthesis and regulation — UV-exposed skin manufactures vitamin D (needed for calcium absorption and bone health) and limits water loss so the body does not dehydrate through its surface. Skin also absorbs (transdermal medications) and excretes small amounts of waste in sweat.
Skin across the lifespan
Skin is not static. Infants have thinner, less pigmented skin — they lose heat and fluids faster and sunburn easily. Older adults have thinner epidermis and dermis, less oil and sweat (dry, fragile skin), less subcutaneous fat, slower cell turnover, and reduced sensation — all increasing vulnerability to injury, pressure damage, and delayed healing. Knowing what is normal for the age group prevents both over-alarming and under-recognizing.
Common Confusions
| Do Not Confuse | With | Difference |
|---|---|---|
| Epidermis | Dermis | Epidermis: thin outer barrier, no blood vessels. Dermis: deeper layer with vessels, nerves, glands |
| Subcutaneous fat loss (aging) | "Aging you can't prevent" | Normal aging, but its consequences (pressure injury, fragile skin) are preventable |
| Redness that blanches | Redness that doesn't | Blanching = reversible irritation; non-blanching = deeper damage (key pressure-injury sign) |
| No visible redness = healthy skin | No visible redness = no problem | On darker skin, redness is harder to see — check warmth, texture, baseline, and ask about discomfort |
| Skin color change | A sign that looks the same for everyone | Color changes present differently across skin tones; check mucous membranes, nail beds, sclera |
| Sweat glands | Sebaceous glands | Sweat glands cool the body; sebaceous glands make conditioning oil |
| The skin as a "wrapper" | The skin as an organ | It regulates temperature, makes vitamin D, senses, absorbs, and defends |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Your skin is like a three-layer suit of armor you wear your whole life. The outside layer is the armor's shiny coat — it takes the scrapes and blocks the rain. The middle layer is the padding and wiring — blood tubes and feeling-wires. The bottom layer is the warm, fluffy lining that keeps you cozy. When the armor gets a scratch, repair crews fix it — and nurses are the people who check that the armor is in good shape and help it heal.
Worked example
A nurse assesses Mrs. Okafor, 78, admitted after a fall, and uses layer knowledge to interpret three findings:
- A red patch over her sacrum. The nurse checks whether the redness blanches (turns pale when pressed and refills). Blanching redness suggests the epidermis is irritated but blood flow works; non-blanching redness suggests deeper (dermal) damage — an early pressure-injury warning. Layer knowledge tells her the redness reflects dilated dermal vessels, and any wound here will be deeper and slower to heal than a surface scrape.
- Dry, flaky legs with fine wrinkles. Thin, dry older-adult skin: less oil, less collagen, less padding. She plans gentle cleansing, moisturizing per facility policy, and handling that avoids friction — the barrier is fragile.
- Slow-returning turgor on the hand. She documents it as a possible hydration finding and reports it, connecting skin signs to fluid status.
She documents each finding separately — the observation ("non-blanching redness 3 cm over sacrum") and the interpretation ("possible early pressure injury") — so the team can act on facts.
Key takeaways
- The skin has three layers: epidermis (thin barrier, no blood vessels), dermis (vessels, nerves, glands, hair follicles), hypodermis/subcutaneous (fat: insulation, cushion, energy).
- Keratin makes skin, hair, and nails tough and waterproof.
- The epidermis is fed by diffusion from the dermis — damage to the dermis is what bleeds and hurts.
- Melanin colors skin and absorbs UV; erythema, pallor, and jaundice look different on different skin tones — assess against baseline, including mucous membranes and nail beds.
- Sebaceous glands make sebum (oil); sweat glands (eccrine, apocrine) make sweat — both support the barrier and temperature control.
- Headline functions: protection, thermoregulation, sensation, vitamin D synthesis, water-loss prevention — plus absorption (transdermal meds) and minor excretion.
- Older-adult skin is thinner, drier, less padded, slower to heal — a major reason for pressure-injury risk.
- The subcutaneous layer is the target for subcutaneous injections — anatomy drives technique.
- Educational overview only: structural details (exact cell layers, gland subtypes, turnover times) vary by source; verify specifics against your textbook and current references.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
Why does a superficial scrape on the epidermis heal without bleeding, while a cut reaching the dermis bleeds and hurts more?
Show answer
The epidermis has no blood vessels — it is fed by diffusion — so a scrape confined to it does not bleed and is mostly painless. The dermis contains vessels and nerves, so a cut there bleeds, hurts, scars differently, and takes longer to heal.
Name the three skin layers outside-in and one major job of each.
Show answer
Epidermis — waterproof protective barrier. Dermis — strength, sensation, temperature control via vessels, nerves, glands, hair follicles. Hypodermis — fat that insulates, cushions, and stores energy.
Why is it important to know a patient's baseline skin color before assessing for redness?
Show answer
Redness, pallor, and jaundice present differently on different skin tones. Without a baseline you can miss early pressure injury or misinterpret normal color as a problem. Check mucous membranes, nail beds, and sclera, and ask about baseline.
List four skin functions and one nursing implication for each.
Show answer
Protection (keep the barrier intact → infection prevention); thermoregulation (sweat and vessel changes → monitor heat/cold tolerance); sensation (pain/pressure/temperature → patients who can't feel need scheduled repositioning); vitamin D synthesis and water-loss prevention (UV exposure and hydration matter). Also absorption: apply transdermal patches to clean, intact skin.
A 75-year-old patient has dry, fragile skin and prominent bony areas. What structural changes of aging explain this, and what does it mean for care?
Show answer
Aging thins the epidermis and dermis, reduces oil and sweat, loses subcutaneous fat, and slows cell turnover — leaving skin dry, fragile, and less padded over bone. Care: gentle handling, avoid friction/shear, moisturize per policy, frequent skin inspection, scheduled repositioning.
Where are subcutaneous injections deposited, and why does that location matter for technique?
Show answer
Subcutaneous injections are deposited in the hypodermis, between skin and muscle. Needle depth and angle (and pinch technique) are designed for that layer — too shallow hits the dermis, too deep hits muscle — so technique follows anatomy.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Epidermis
- Outermost layer; tough, waterproof barrier of mostly dead keratin-filled cells
- Dermis
- Middle layer with blood vessels, nerves, glands, hair follicles
- Hypodermis (subcutaneous layer)
- Deepest layer of fat and connective tissue
- Keratin
- Tough protein that fills skin, hair, and nail cells
- Melanin
- Pigment from melanocytes that colors skin and absorbs UV
- Sebum
- Oil from sebaceous glands that conditions and waterproofs skin and hair
- Thermoregulation
- The body's temperature control
- Erythema
- Redness from increased blood flow
- Turgor
- How quickly skin returns to place when pinched
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.