Pharmacology for Nurses · Dermatologic Disorder Drugs
Introduction to the Skin and Its Function
On this page 9 sections
In 30 seconds
The skin is the largest organ of the human body, covering roughly 1.5 to 2 square meters in an average adult. It is easy to think of it as a passive wrapper, but the skin is a highly active, layered organ that protects, senses, regulates, and defends. For pharmacology, the skin matters twice over: it is a target for drugs (ointments, creams, patches, and injectables used to treat skin disease) and a route for drugs (a large fraction of topically applied medication must cross the skin to act, and some drugs are designed to pass through it into the bloodstream). This topic builds the anatomy-and-function foundation you need before studying acne drugs, psoriatic drugs, and topical anti-infectives for burns in the rest of this chapter.
The skin is organized into three main layers — the Epidermis The thin, outer, bloodless layer of skin; its surface is the stratum corneum Full entry → (outer), the Dermis The thick middle layer with blood vessels, collagen, nerves, and glands Full entry → (middle), and the Hypodermis The deepest layer of fat and connective tissue (deep) — plus the appendages rooted within them: hair follicles, sebaceous (oil) glands, and sweat glands. Every drug discussed in this chapter interacts with one or more of these structures, so knowing what each layer does is not busywork; it is the difference between memorizing drug names and actually understanding why they work.
Why this matters
- Topical drug delivery depends on the barrier: The same cream behaves differently on intact skin, hydrated skin, and broken skin. Understanding absorption explains why a nurse must assess skin integrity before applying a topical drug.
- Skin assessment is a nursing superpower: The skin reflects oxygenation (cyanosis, pallor), liver function (jaundice), hydration (turgor), and systemic illness. Many adverse drug reactions — rashes, photosensitivity, and rare severe reactions — first appear on the skin, and the nurse is usually the first to see them.
- Infection and breakdown prevention: Pressure injuries, wound infection, and burn complications are all skin-barrier failures. Preventing them is a core nursing responsibility in every setting, from hospitals to home care.
- Patient teaching: People use dozens of over-the-counter skin products. A nurse who can explain why the Stratum corneum The outermost "bricks and mortar" layer of dead keratin-filled cells and lipids Full entry → limits absorption — and why washing a medication off too soon reduces its effect — turns good therapy into effective therapy.
The college version
Core Concepts
The three layers: epidermis, dermis, hypodermis
The epidermis is the thin, avascular outer layer that you can see and touch. Its outermost portion, the stratum corneum, is made of flat, dead, keratin-filled cells (corneocytes) embedded in a lipid matrix — commonly described as a "bricks and mortar" wall. Below it, living Keratinocytes The main cell type of the epidermis, producing keratin Full entry → divide and slowly migrate outward, replacing the surface cells. The epidermis also contains Melanocytes Pigment-producing cells in the epidermis Full entry → (pigment-producing cells), Langerhans cells (immune sentinels), and touch receptors. Because the epidermis has no blood vessels, it receives oxygen and nutrients by diffusion from the dermis below.
The dermis is the thick, vascular middle layer that gives skin its strength and elasticity. It contains collagen and elastin fibers, blood vessels, nerves, hair follicles, sebaceous glands, and sweat glands. Most topical drugs that penetrate the epidermis end up being picked up by dermal capillaries — which is how a skin-applied drug can reach the systemic circulation.
The hypodermis (subcutaneous layer) is the deepest layer, made mostly of adipose tissue. It insulates, cushions, and stores energy, and it anchors the skin to underlying muscle and bone. Drugs injected into this layer (subcutaneous injections) are absorbed more slowly than into the dermis because of the lower blood flow.
The barrier: what the stratum corneum actually does
The stratum corneum is the rate-limiting barrier for drug absorption through intact skin. Its corneocytes and lipids resist water loss (keeping body fluids in) and block water and microbes from getting in. This is why:
- Intact skin absorbs drugs slowly and in limited amounts — most topical drugs act locally rather than systemically.
- Damaged skin absorbs far more — a burn, abrasion, or eczema flare can turn a "local" drug into a systemic one.
- Occlusion Covering skin (e.g., with a dressing or wrap) so moisture is trapped Full entry → (covering skin with a dressing or wrap) traps moisture, hydrates the stratum corneum, and can substantially increase absorption — sometimes intentionally (occlusive dressings boost potency) and sometimes accidentally (a diaper or bandage over a medicated area).
How drugs cross the skin
Percutaneous (through-the-skin) absorption happens in steps: drug release from the vehicle (cream, ointment, gel), partition into the stratum corneum, diffusion through it, then entry into the viable epidermis and dermal capillaries. Factors that speed or slow this process:
- Lipid solubility: Lipid-soluble drugs cross the lipid-rich stratum corneum far more easily than water-soluble ones.
- Molecular size: Small molecules penetrate better than large ones.
- Skin integrity: Broken, inflamed, or macerated skin absorbs more.
- Hydration and occlusion: Moisture swells corneocytes and increases permeability.
- Site: Skin thickness varies — eyelids and genitals absorb more readily than palms and soles, which have a thick stratum corneum.
- Age and circulation: Infant skin is thinner; skin blood flow changes with age, temperature, and perfusion.
- Contact time and surface area: Longer contact and larger area mean more total absorption.
These factors matter clinically: a topical corticosteroid applied to the thin skin of the face can produce stronger effects (and more risk of local side effects) than the same product on the palms.
The skin as a mirror of health and a target of drug reactions
Skin findings are clinical data. Color changes (pallor, erythema, cyanosis, jaundice), temperature, moisture, turgor, and lesions all carry information. When a person starts a new medication, the nurse watches the skin for expected effects and for adverse reactions, which range from mild photosensitivity (e.g., some acne and psoriatic drugs make skin sun-sensitive) to rare but serious reactions such as severe blistering rashes. The rule in nursing assessment is to describe what you see (location, size, color, shape, texture, distribution) rather than to guess a diagnosis — the prescriber and dermatology team interpret findings.
Skin, person-first
Skin disease is visible, and visible disease carries stigma. People with acne, psoriasis, eczema, or scars are often embarrassed or self-conscious, and their condition affects quality of life far beyond the physical. Nursing language and behavior should be person-first ("a person with psoriasis," not "a psoriatic") and should treat the person's concerns about appearance, adherence, and daily routines as legitimate clinical issues, not trivia.
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Epidermis | Dermis | Epidermis is the avascular outer layer (the barrier); dermis is the vascular middle layer with collagen and glands |
| "Skin absorbs everything" | "Skin is a strong barrier" | Intact stratum corneum limits absorption; significant absorption through intact skin is slow and incomplete — occlusion and damage change the picture |
| Sweating as a major route of drug excretion | Renal and hepatic excretion | Drugs are eliminated mainly by kidneys and liver; sweat removes only trace amounts of most drugs |
| A topical drug's local effect | Its systemic effect | On intact skin most topical drugs act locally; on damaged or occluded skin systemic effects become more likely |
| Describing a skin finding | Diagnosing it | Nurses describe location, size, color, shape, and texture; the prescriber/team interprets and diagnoses |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Your skin is like a three-layer raincoat that covers your whole body. The outside layer is a brick wall made of tiny dead cells that keeps water and germs out — that wall is also why medicine rubbed on the skin soaks in slowly. The middle layer is full of blood vessels, like little roads that carry things around. If you scrape or burn the wall, medicine can get through much faster, which is why hurt skin needs extra care and extra watching.
Worked example
Consider a topical corticosteroid cream prescribed for a person with a localized patch of dermatitis on the forearm, and the same product ordered for a person with a similar patch on the eyelid. The drug class and mechanism are identical, but the outcomes are not: eyelid skin is thin, highly permeable, and frequently occluded by blinking and natural moisture, so absorption there is much greater per unit area. The nurse's teaching — and the prescriber's plan — reflects this: the person using it on the face may be counseled about lighter application and shorter use, while the forearm user may need guidance about reapplying after handwashing. The lesson generalizes: topical dosing is not one-size-fits-all because skin is not one-size-fits-all. In every case, the nurse documents what was applied, where, and the condition of the skin before and after, and verifies the plan against current references, the formulary, and the prescriber's orders.
Safety note: This example describes drug classes and general principles only. Specific products, potencies, application frequencies, and duration-of-use limits vary by patient, product, and institution — always verify against current references, the facility formulary, and the prescriber's orders.
Key takeaways
- Three layers: epidermis (outer, avascular, contains the stratum corneum barrier), dermis (vascular, strength and glands), hypodermis (fat, insulation, cushioning).
- The stratum corneum is the rate-limiting barrier to topical drug absorption — "bricks and mortar" of dead keratinocytes plus lipids.
- Absorption is increased by: lipid-soluble drugs, small molecules, broken/inflamed skin, hydration/occlusion, thin-skin sites, larger area, longer contact.
- Most topical drugs act locally on intact skin; systemic effects become more likely when skin is damaged or occluded.
- Skin assessment = describe, don't diagnose: note color, moisture, temperature, turgor, and lesion characteristics.
- Skin is a window on drug reactions: rashes, photosensitivity, and severe blistering reactions often appear first on skin.
- Person-first language and respect for the psychosocial impact of visible skin disease are professional standards.
Check yourself
5 review questions from the chapter. Try each one, then open the answer.
Name the three layers of the skin and one major function of each.
Show answer
Epidermis — barrier and pigment production; dermis — strength, blood supply, glands, sensation; hypodermis — insulation, cushioning, energy storage.
Why is the stratum corneum called the rate-limiting barrier for topical drugs?
Show answer
Because its dense layers of dead keratinocytes and lipids are the slowest step in absorption — everything a topical drug does depends on crossing it first.
List four factors that increase drug absorption through the skin.
Show answer
Lipid-soluble drug, small molecular size, damaged/inflamed skin, hydration/occlusion, thin-skin sites, larger surface area, longer contact time.
Why might a drug applied to broken skin produce systemic effects when the same drug on intact skin does not?
Show answer
The barrier is lost or thinned, so a much larger fraction of the drug reaches dermal capillaries and the systemic circulation.
What should a nurse document when assessing a skin lesion, and why not label it with a diagnosis?
Show answer
Describe objectively: location, size, color, shape, borders, texture, distribution, and any associated symptoms (itching, pain). Labeling a diagnosis can bias assessment and exceeds nursing assessment scope.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Epidermis
- The thin, outer, bloodless layer of skin; its surface is the stratum corneum
- Stratum corneum
- The outermost "bricks and mortar" layer of dead keratin-filled cells and lipids
- Dermis
- The thick middle layer with blood vessels, collagen, nerves, and glands
- Hypodermis
- The deepest layer of fat and connective tissue
- Keratinocytes
- The main cell type of the epidermis, producing keratin
- Melanocytes
- Pigment-producing cells in the epidermis
- Occlusion
- Covering skin (e.g., with a dressing or wrap) so moisture is trapped
- Percutaneous absorption
- The passage of a drug through the skin into deeper layers and blood
- Transepidermal water loss
- Water that evaporates through the skin barrier
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
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