Which layer of the hair shaft contains melanin and is responsible for hair color?

Cortex. The cortex is the middle layer of the hair shaft and makes up about 90% of the hair. It contains melanin (the pigment that determines hair color), and is responsible for hair strength, elasticity, and texture. The cuticle is the outer protective layer, and the medulla is the inner core.

During which phase of the hair growth cycle is the hair actively growing?

Anagen. The anagen phase is the active growth phase of the hair cycle, lasting 2-7 years. About 85% of scalp hair is in the anagen phase at any time. Catagen is the transition phase, telogen is the resting phase, and exogen is the shedding phase.

The nail matrix is critical because:

If damaged, the nail will be permanently deformed. The nail matrix is where all nail plate cells are produced. If the matrix is damaged, the nail will be permanently deformed because the cells that form the nail plate originate there. The lunula is the visible portion of the matrix.

Anatomy & Physiology - Hair & Nails — Free Study Guide 2026

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.

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

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:

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

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

Cosmetology License

2.4 Anatomy & Physiology - Hair & Nails