Key Takeaways
- The hair shaft has three layers: cuticle (outer protective), cortex (strength and color), medulla (inner core).
- Hair growth cycle has three phases: anagen (growth, 2-7 years), catagen (transition, 2-3 weeks), telogen (rest, 3-4 months).
- The nail matrix is the origin of the nail plate and, if damaged, causes permanent nail deformity.
- The lunula is the visible white crescent at the nail base - part of the matrix.
- Normal hair shedding is 50-100 hairs per day from telogen phase follicles.
Last updated: January 2026
Anatomy & Physiology - Hair & Nails
Understanding hair and nail structure, growth cycles, and disorders is fundamental knowledge for cosmetologists. This section covers the anatomy you need for the NIC exam.
Part 1: Hair Anatomy
Hair Structure Overview
Hair is composed primarily of keratin, the same protein found in skin and nails. Each hair consists of two main parts:
- Hair Follicle: Living structure below the skin surface
- Hair Shaft: Nonliving visible portion above the skin
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The Hair Shaft - Three Layers
| Layer | Location | Composition | Function |
|---|---|---|---|
| Cuticle | Outermost | Overlapping scales (like roof shingles) | Protection, determines shine and texture |
| Cortex | Middle (90% of hair) | Elongated cells, melanin, keratin | Strength, elasticity, color |
| Medulla | Innermost core | Air spaces and cells | Insulation (may be absent in fine hair) |
The Cuticle:
- Transparent, colorless layer
- Scales point away from the scalp (root to tip)
- Healthy cuticle = smooth, shiny hair
- Damaged cuticle = dull, rough, tangled hair
- Chemical services open and affect the cuticle
The Cortex:
- Contains the majority of the hair's structure
- Location of melanin (pigment)
- Responsible for:
- Hair color
- Strength and elasticity
- Texture (straight, wavy, curly)
- Target of permanent color, perms, and relaxers
The Medulla:
- Central core of the hair
- May be continuous, fragmented, or absent
- More common in coarse, thick hair
- Often absent in fine, vellus hair
- Function not fully understood
The Hair Follicle
| Structure | Description | Function |
|---|---|---|
| Hair Bulb | Club-shaped base of follicle | Contains cells for growth |
| Dermal Papilla | Cone-shaped elevation at bulb base | Blood supply and nutrients |
| Arrector Pili | Tiny muscle attached to follicle | Creates "goosebumps" |
| Sebaceous Gland | Oil gland connected to follicle | Lubricates hair and skin |
Hair Growth Cycle
Hair grows in a continuous cycle with three distinct phases:
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Phase 1: Anagen (Growth Phase)
- Duration: 2-7 years (determines maximum hair length)
- Percentage: 85% of scalp hair is in anagen
- Activity: Active cell division at the hair bulb
- Characteristics:
- Hair grows approximately 0.5 inches per month
- Longer anagen = longer potential hair length
- Affected by genetics, age, health, and hormones
Phase 2: Catagen (Transition Phase)
- Duration: 2-3 weeks
- Percentage: 1-2% of scalp hair
- Activity: Growth stops, follicle shrinks
- Characteristics:
- Hair detaches from dermal papilla
- Follicle shrinks to about 1/6 of original length
- Signals the end of active growth
Phase 3: Telogen (Resting Phase)
- Duration: 3-4 months
- Percentage: 10-14% of scalp hair
- Activity: Follicle is dormant
- Characteristics:
- Hair remains in follicle but is not growing
- New hair begins to form beneath
- At end of telogen, old hair sheds
Exogen (Shedding)
- Old hair is released from the follicle
- Normal shedding: 50-100 hairs per day
- New anagen hair pushes out old telogen hair
- Excessive shedding may indicate disorder
Hair Disorders
Types of Alopecia (Hair Loss)
| Condition | Cause | Characteristics | Treatment |
|---|---|---|---|
| Androgenic Alopecia | Genetics, hormones (DHT) | Male/female pattern baldness | Minoxidil, finasteride |
| Alopecia Areata | Autoimmune | Patchy, round bald spots | May regrow spontaneously |
| Telogen Effluvium | Stress, illness, childbirth | Diffuse shedding | Treat underlying cause |
| Traction Alopecia | Tight hairstyles | Hair loss at hairline/temples | Change styling practices |
| Anagen Effluvium | Chemotherapy | Rapid, widespread loss | Hair regrows after treatment |
Scalp Disorders
| Condition | Description | Action |
|---|---|---|
| Dandruff (Pityriasis) | Flaky scalp, dry or oily | Can perform service with medicated shampoo |
| Seborrheic Dermatitis | Severe dandruff, oily scales | Refer to dermatologist if severe |
| Psoriasis | Thick silvery scales | Can service if mild; refer if severe |
| Pediculosis (Head Lice) | Parasitic infestation | DO NOT perform service; refer to physician |
| Tinea Capitis | Fungal ringworm | DO NOT perform service; refer to physician |
Hair Shaft Disorders
| Disorder | Description |
|---|---|
| Trichorrhexis Nodosa | Weak points causing breakage |
| Trichoptilosis | Split ends |
| Monilethrix | Beaded hair shaft |
| Canities | Gray/white hair (natural aging) |
| Ringed Hair | Alternating light and dark bands |
Part 2: Nail Anatomy
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Key Nail Structures
| Structure | Description | Function |
|---|---|---|
| Nail Matrix | Origin of nail (under proximal fold) | Produces nail plate cells |
| Lunula | Visible white half-moon | Visible part of matrix |
| Nail Plate | Visible, hardened nail | Protection |
| Nail Bed | Skin beneath nail plate | Supplies nutrients |
| Free Edge | Part extending past fingertip | Functional edge |
| Hyponychium | Skin under free edge | Protects nail bed |
| Eponychium | Living skin at nail base | Protects matrix |
| Cuticle | Dead tissue attached to plate | Seals eponychium to plate |
| Lateral Nail Folds | Skin on sides of nail | Protection, guidance |
The Nail Matrix - Critical Structure
The nail matrix is the most important structure:
- Origin of all nail plate cells
- Located beneath the proximal nail fold
- The lunula is the visible portion of the matrix
- If the matrix is damaged, the nail will be permanently deformed
- Matrix cells produce keratin that hardens into nail plate
Nail Growth
- Rate: Approximately 0.1mm per day (3mm per month)
- Fingernails: Replace completely in 4-6 months
- Toenails: Replace completely in 12-18 months
- Factors affecting growth: age, health, nutrition, season
Nail Disorders and Diseases
Nail Disorders (Can Usually Service)
| Disorder | Description | Cause |
|---|---|---|
| Leukonychia | White spots | Minor trauma to matrix |
| Onychorrhexis | Brittle, splitting nails | Age, chemicals, dryness |
| Beau's Lines | Horizontal ridges | Illness, stress, trauma |
| Hangnails | Torn cuticle/skin | Dryness, nail biting |
| Ridges | Vertical lines | Aging, normal variation |
| Eggshell Nails | Thin, flexible nails | Illness, malnutrition |
Nail Diseases (DO NOT Service)
| Disease | Description | Action |
|---|---|---|
| Onychomycosis | Fungal infection; thick, discolored | Refer to physician |
| Paronychia | Infection around nail fold | Refer to physician |
| Onychia | Inflammation with pus | Refer to physician |
| Pseudomonas (Greenies) | Green/black bacterial infection | Refer to physician |
| Onycholysis | Nail separating from bed | May indicate underlying condition |
| Tinea Pedis (Athlete's Foot) | Fungal skin infection | Refer if active |
When to Refuse Nail Service
Never perform nail services on clients with:
- Signs of infection (redness, swelling, pus, pain)
- Fungal infections (discolored, thick, crumbly nails)
- Open wounds or cuts around the nail
- Visible bacterial infections (green/black discoloration)
- Any condition that appears contagious
Test Your Knowledge
Which layer of the hair shaft contains melanin and is responsible for hair color?
A
B
C
D
Test Your Knowledge
During which phase of the hair growth cycle is the hair actively growing?
A
B
C
D
Test Your Knowledge
The nail matrix is critical because:
A
B
C
D