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🌿 SKIN STRUCTURE, DISORDERS & DISEASES – (Study Guide)
🧍♀️ Overview of the Skin
The largest organ of the body by weight & length.
Average adult skin covers ≈ 3,000 sq in and weighs 6–9 lbs.
Protects muscles, bones, nerves, blood vessels, and internal organs.
Thinnest: under eyes & eyelids | Thickest: palms & soles.
Healthy skin = slightly moist, soft, flexible, clear, glowing, even tone.
Surface: slightly acidic (pH ≈ 5.5) & has quick immune responses.
Appendages: hair, nails, sweat & oil glands.
Callus : thickened skin caused by repeated pressure—protects underlying tissue; never remove completely.
Dermatology : medical study of skin structure, function, diseases, treatment.
Dermatologist : physician who treats skin conditions.
Nail technicians CANNOT diagnose, prescribe, or treat diseases.
🩸 LAYERS OF THE SKIN
1️⃣ Epidermis (Outermost layer)
Thinnest layer; no blood vessels; made of keratinized cells.
Five sub-layers:
| Layer | Description |
|---|---|
| Stratum Corneum | Horny outer layer; protects from UV rays, pollution, bacteria; cells shed & renew every 25–28 days. |
| Stratum Lucidum | Clear layer allowing light through; only on palms & soles; forms fingerprints. |
| Stratum Granulosum | Grainy layer; cells die & replace those shed above. |
| Stratum Spinosum | Spiny layer; contains Langerhans immune cells to defend against infection. |
| Stratum Germinativum | Basal layer; produces new cells via mitosis; contains melanocytes → melanin. |
Skin Color & Melanin
Color depends on melanin, a hereditary trait.
Pheomelanin = red-yellow (light skin) | Eumelanin = brown-black (dark skin).
Melanin protects cells from UV damage.
Sunscreen SPF 15–30 reduces burn & premature aging.
2️⃣ Dermis (True Skin / Derma / Corium / Cutis)
Inner, highly sensitive layer (~ 25× thicker than epidermis).
Contains blood & lymph vessels, nerves, glands, and hair follicles.
Two layers:
Papillary Layer (upper 10–20%) → looped capillaries, lymphatics, and tactile corpuscles for touch/pressure.
Reticular Layer (deeper) → supplies oxygen & nutrients; houses sweat & oil glands, hair follicles, arrector pili muscles (goose bumps), nerve endings, collagen, elastin.
3️⃣ Hypodermis (Subcutaneous / Adipose tissue)
Fatty layer beneath dermis.
Gives smoothness & contour; stores fat-soluble vitamins & hormones.
Acts as cushion & energy reserve.
Thickness varies by age, gender, health.
⚡ Nerves of the Skin
Motor fibers: to arrector pili → goose bumps.
Sensory fibers: sense heat, cold, touch, pressure, pain → messages to brain.
Secretory fibers: to sweat & oil glands → regulate perspiration & sebum flow.
💪 Strength & Flexibility
Collagen (≈ 70%) → strength & structure.
Elastin (≈ 15%) → stretch & return to shape.
💧 GLANDS OF THE SKIN
| Gland Type | Location/Function |
|---|---|
| Sudoriferous (Sweat) | Regulate temperature & waste removal. |
| • Apocrine | Linked to hair follicles (underarms, genitals, scalp); activated by puberty, emotion, stress; produce odor. |
| • Eccrine | All over body; active after birth; help cool body. |
| Sebaceous (Oil) | Connected to hair follicles; secrete sebum to lubricate skin & hair. |
| • Imbalance | Blocked follicle → papule or pustule (acne); refer client to dermatologist. |
🩸 Skin Nutrition & Functions
Blood supplies oxygen & nutrients (only from inside the body).
Six Primary Functions
Protection – barrier from injury, bacteria, chemicals, water loss.
Sensation – nerve endings detect stimuli & send signals to brain.
Heat Regulation – maintain ≈ 98.6 °F (37 °C) via sweating & blood flow.
Excretion – sweat removes salts & wastes.
Secretion – sebum keeps skin soft, hair shiny.
Absorption – only small molecules can enter via pores/follicles; most cosmetics stay surface-level.
🥗 Maintaining Healthy Skin
Nutrition
Converts proteins, carbs, fats → energy.
Provides vitamins, minerals, enzymes, water, essential fatty acids.
Vitamins
| Type | Examples | Functions | Sources |
|---|---|---|---|
| Oil-soluble | A, D, E, K | Stored in fat tissue | Various foods |
| Water-soluble | B, C | Used quickly, excreted | Fruits & veggies |
A: cell repair, elasticity; found in liver, carrots, kale.
C: collagen formation, healing, anti-aging; found in citrus, peppers, kiwi.
D: calcium absorption, bone health; from sun & fatty fish.
E: UV protection, elasticity, wound healing; almonds, avocado.
K: blood clotting, bone strength; leafy greens, green tea.
Water
Body ≈ 60% water; essential for metabolism, digestion, and temperature control.
Dehydration → fatigue, poor focus, dry/cracked skin.
Excess water → hyponatremia (low blood sodium).
Drink clean water for healthy cells & toxin elimination.
☀️ Sun & Aging Effects
80–85 % of skin aging due to sun exposure.
UV = invisible energy, not light.
| Type | Nickname | Effect |
|---|---|---|
| UVA | Aging rays | Break down collagen, cause wrinkles |
| UVB | Burning rays | Cause sunburn, DNA damage, skin cancer |
Pollution, smoking, alcohol, poor diet → accelerate aging.
🩹 SKIN DISORDERS & DISEASES
Symptoms:
Subjective (what you feel): itching, burning, pain.
Objective (what you see): rash, blister.
Lesions
A mark on skin showing injury or change in tissue.
Primary Lesions: color change or raised (bulla, cyst, macule, nodule, papule, pustule, tumor, vesicle, wheal).
Secondary Lesions: crust, excoriation, fissure, keloid, scale, scar, ulcer.
🩺 Primary Skin Lesions
Primary lesions are changes in the skin that are the first visible signs of a skin disorder or disease. They can appear as spots, bumps, blisters, or swellings.
1. Macule (MAK-yool)
Description:
Flat spot or discoloration on the skin.
Usually brown, tan, or red.
Not raised or sunken.
Examples:
Freckle
Age spot
Key Point:
No change in skin texture—only in color.
2. Papule (PAP-yool)
Description:
Small, raised, solid bump on the skin.
Does not contain pus.
Examples:
Pimple (without pus)
Elevated mole
Key Point:
A papule can develop into a pustule if pus forms.
3. Pustule (PUS-tyool)
Description:
Inflamed, raised bump that contains pus.
Usually red around the base.
Examples:
Acne pustule
Whitehead
Key Point:
Indicates infection or inflammation.
4. Vesicle (VES-ih-kul)
Description:
Small blister containing clear fluid.
Examples:
Poison ivy blisters
Herpes simplex (cold sore)
Key Point:
Less than 1 cm in diameter.
5. Bulla (BULL-ah)
Description:
Large blister containing watery fluid.
Similar to a vesicle but larger.
Examples:
Contact dermatitis
Second-degree burn
Bullous impetigo
Key Point:
Requires medical referral.
6. Cyst or Tubercle (SIST / TOO-ber-kuhl)
Description:
Closed, thick-walled sac under the skin containing fluid, pus, or semi-solid material.
Examples:
Sebaceous cyst
Severe acne nodule
Key Point:
Requires medical referral; can cause scarring.
7. Wheal (WHEEL)
Description:
Itchy, swollen lesion that lasts only a few hours.
Often caused by an allergic reaction.
Examples:
Mosquito bite
Hives
Key Point:
If it lasts more than 3 days, seek medical advice.
Inflammations
Dermatitis: general inflammation (vesicles or papules).
Eczema: itchy & painful; non-contagious.
Cellulitis: swollen, red, hot area; not spread person-to-person.
Psoriasis: red patches with white scales; fast cell turnover.
🧬 Skin Cancer
Caused by excessive sun exposure.
Types: Basal Cell Carcinoma → Squamous Cell Carcinoma → Malignant Melanoma.
ABCDE Checklist (American Cancer Society)
| Letter | Meaning |
|---|---|
| A | Asymmetry – halves don’t match |
| B | Border – edges ragged or notched |
| C | Color – uneven shades |
| D | Diameter – larger than ¼ inch |
| E | Evolution – changes in size, shape, color |
🦠 Infectious Skin Disorders
| Disorder | Cause | Symptoms | Contagious? |
|---|---|---|---|
| Herpes Simplex | Virus | Blister clusters around mouth/nose/genitals | Yes |
| Verruca (Wart) | Virus | Raised growths on skin | Yes |
| Tinea Manus | Fungus | Ring-shaped blisters on hand | Yes |
| Tinea Pedis (Athlete’s Foot) | Fungus | Itchy, peeling skin between toes | Yes |
🧤 Prevention for Nail Technicians
Dermatitis = skin inflammation.
Contact Dermatitis from irritants or allergens (monomers, gels, wraps).
Irritant type: from harsh substances.
Allergic type: from repeated exposure to chemicals.
Causes: over-wet beads, under-cured gel enhancements, dirty tools.
Protection: wash hands, disinfect tools/surfaces, wear nitrile gloves.
✅ STUDY TIPS
Review all skin layers and functions daily.
Memorize vitamin roles & sources.
Know UVA vs UVB effects.
Understand common skin disorders & their symptoms.
Never diagnose clients — refer to dermatologist when needed.