Overview
Trichology is the scientific branch of dermatology focused on the study of hair, its diseases, and proper care. For the Texas Cosmetology State Board Exam, you must understand the structural layers of the hair, the chemical bonds within the hair shaft, the phases of the hair growth cycle, and how to identify common scalp conditions and disorders. Knowing when to treat a client versus when to refer to a physician is critical both for the exam and for professional practice.
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Hair Structure
The Hair Shaft: Three Layers
The hair shaft is composed of three concentric layers, each with a distinct function:
| Layer | Location | Function |
|-------|----------|----------|
| Cuticle | Outermost | Protective scale-like layer; guards the inner layers |
| Cortex | Middle | Provides strength, elasticity, and contains melanin (color) |
| Medulla | Innermost core | Soft, sometimes hollow; least understood layer |
> Memory Tip: Think C–C–M (outside to inside): Cuticle → Cortex → Medulla
Key Hair Structures
• Hair follicle – The tube-like pocket in the skin from which the hair grows and receives nourishment
• Dermal papilla – Located at the base of the follicle; contains blood vessels and nerves that supply nutrients and trigger new hair cell production
• Arrector pili muscle – Small involuntary muscle attached to the follicle; contracts when cold or frightened, causing the hair to stand erect and producing "goosebumps"
• Sebaceous glands – Oil glands attached to the follicle that secrete sebum, the scalp's natural oil
Chemical Bonds in the Hair
Understanding which bonds are broken by which processes is a frequent exam topic:
| Bond Type | Strength | Broken By | Re-formed By |
|-----------|----------|-----------|--------------|
| Hydrogen bonds | Weak (temporary) | Water or heat | Drying or cooling |
| Disulfide bonds | Strong (permanent) | Alkaline chemicals (e.g., perm solutions) | Neutralizer |
| Salt bonds | Moderate | Changes in pH | Returning to normal pH |
#### Key Terms – Hair Structure
• Trichology – The scientific study of hair, its diseases, and care; a branch of dermatology
• Melanin – Pigment granules in the cortex that determine natural hair color
• Keratin – The protein that makes up the primary structure of the hair shaft
• Sebum – Natural oil secreted by sebaceous glands to lubricate the hair and scalp
#### Watch Out For ⚠️
• Do not confuse hydrogen bonds (broken by water/heat) with disulfide bonds (broken by chemicals). Exam questions frequently test this distinction.
• The cortex contains melanin — not the cuticle or medulla.
• The dermal papilla nourishes the follicle — do not confuse it with the arrector pili muscle.
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Hair Growth Cycle
The Three Phases
```
ANAGEN → CATAGEN → TELOGEN
(Growth) (Transition) (Rest/Shed)
```
| Phase | Name | Duration | What Happens |
|-------|------|----------|--------------|
| Anagen | Growth phase | 2–7 years | Active hair production; ~90% of hairs in this phase |
| Catagen | Transition phase | ~2–3 weeks | Follicle shrinks; growth stops; hair detaches from papilla |
| Telogen | Resting/Shedding phase | ~3–4 months | Hair rests, then sheds; 50–100 hairs/day is normal |
Key Facts to Memorize
• 90% of scalp hairs are in anagen at any given time
• 50–100 hairs per day shed is considered normal during telogen
• The anagen phase determines potential hair length — longer anagen = longer hair
• After telogen, the follicle re-enters anagen and a new hair begins growing
#### Key Terms – Hair Growth
• Anagen – Active growth phase
• Catagen – Brief transitional phase; follicle shrinks
• Telogen – Resting and shedding phase
#### Watch Out For ⚠️
• Shedding more than 100 hairs/day may indicate a disorder — but shedding up to 100 hairs/day is normal.
• Know the correct order: Anagen → Catagen → Telogen (not the reverse).
• The anagen phase lasts years, while catagen lasts only weeks.
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Scalp Conditions & Disorders
Dandruff (Pityriasis)
Dandruff is the most common scalp disorder cosmetologists encounter. The technical term is pityriasis.
| Type | Characteristics |
|------|----------------|
| Pityriasis capitis simplex | Dry dandruff – small, white, loose flakes; not attached to scalp |
| Pityriasis steatoides | Oily dandruff – waxy, yellow, greasy scales that stick to the scalp |
Common Scalp Conditions
| Condition | Cause | Key Characteristics | Cosmetologist's Role |
|-----------|-------|---------------------|----------------------|
| Seborrhea | Overactive sebaceous glands | Excess oil (sebum) production; oily scalp | Can perform scalp treatments |
| Tinea capitis | Fungal infection | Circular, scaly patches; hair loss; highly contagious | Refer to physician — do NOT service |
| Pediculosis capitis | Head lice (parasitic) | Infestation; highly contagious; severe itching | Refer to physician — do NOT service |
The Golden Rule: When to Refer
> ⚠️ A cosmetologist must NEVER attempt to treat any contagious, infectious, inflamed, or open scalp condition. Always refer to a physician.
This includes:
• Tinea capitis (ringworm of the scalp)
• Pediculosis capitis (head lice)
• Open sores or lesions on the scalp
• Any condition that appears infectious or inflamed
#### Key Terms – Scalp Conditions
• Pityriasis – Technical term for dandruff; excessive shedding of dead scalp skin cells
• Tinea capitis – Ringworm of the scalp; fungal infection; highly contagious
• Pediculosis capitis – Head lice infestation; parasitic; highly contagious
• Seborrhea – Overproduction of sebum by the sebaceous glands; leads to oily scalp
#### Watch Out For ⚠️
• Tinea capitis is caused by a fungus, not a worm — despite the name "ringworm."
• Dry dandruff = simplex (simple); Oily dandruff = steatoides (think "steat" = fat/oil).
• Cosmetologists are not licensed to diagnose or treat medical conditions — this is a boundary that appears frequently on the exam.
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Hair Loss & Alopecia
Types of Alopecia
| Type | Description | Cause |
|------|-------------|-------|
| Alopecia areata | Sudden patchy hair loss in round/irregular areas; no scarring | Autoimmune — immune system attacks hair follicles |
| Androgenetic alopecia | Hereditary pattern baldness | DHT (dihydrotestosterone) shrinks follicles over time |
| Traction alopecia | Hair loss from excessive tension/pulling | Tight hairstyles (braids, ponytails, extensions) |
Additional Hair Growth Disorders
| Disorder | Definition |
|----------|-----------|
| Alopecia | General term for any abnormal hair loss (partial or complete) |
| Hypertrichosis | Excessive or abnormal hair growth in areas where hair is not normally present; may be caused by hormonal imbalances or medications |
Key Facts to Memorize
• DHT (dihydrotestosterone) is the hormone responsible for androgenetic alopecia
• Traction alopecia can become permanent if the tension is not corrected early
• Alopecia areata is believed to be an autoimmune condition
• Hypertrichosis is abnormal hair growth — the opposite of alopecia
#### Key Terms – Hair Loss
• Alopecia – Abnormal partial or complete hair loss
• Alopecia areata – Autoimmune; sudden patchy hair loss; no inflammation or scarring
• Androgenetic alopecia – Hereditary pattern baldness; caused by DHT
• Traction alopecia – Hair loss caused by prolonged mechanical tension from tight styling
• Hypertrichosis – Abnormal excessive hair growth; caused by hormonal or medication factors
• DHT (Dihydrotestosterone) – The hormone responsible for shrinking follicles in pattern baldness
#### Watch Out For ⚠️
• Androgenetic alopecia ≠ alopecia areata. Know the difference: one is hereditary/hormonal, the other is autoimmune.
• Traction alopecia is preventable — caused by styling choices, not disease.
• Hypertrichosis is excess hair growth; do not confuse with alopecia (hair loss).
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Quick Review Checklist
Use this checklist to confirm you are exam-ready:
Hair Structure
• [ ] Name the three layers of the hair shaft from outside to inside: Cuticle → Cortex → Medulla
• [ ] Know that melanin is found in the cortex
• [ ] Know that hydrogen bonds are broken by water/heat
• [ ] Know that disulfide bonds are broken by alkaline chemicals (perm solutions)
• [ ] Identify the dermal papilla as the blood-vessel-rich structure that nourishes hair growth
• [ ] Identify the arrector pili muscle as the cause of goosebumps
Hair Growth Cycle
• [ ] Memorize the order: Anagen → Catagen → Telogen
• [ ] Know that ~90% of hairs are in anagen at any time
• [ ] Know that 50–100 hairs/day shed is normal
• [ ] Catagen lasts approximately 2–3 weeks
Scalp Conditions
• [ ] Identify pityriasis as the technical term for dandruff
• [ ] Distinguish dry dandruff (simplex) from oily dandruff (steatoides)
• [ ] Recognize tinea capitis as a fungal infection requiring physician referral
• [ ] Recognize pediculosis capitis as head lice requiring physician referral
• [ ] Know that seborrhea = overactive sebaceous glands = oily scalp
Alopecia & Hair Loss
• [ ] Know alopecia as the general term for hair loss
• [ ] Identify alopecia areata as autoimmune and patchy
• [ ] Identify androgenetic alopecia as hereditary; caused by DHT
• [ ] Identify traction alopecia as caused by tight hairstyles
• [ ] Know hypertrichosis as abnormal excess hair growth
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> Final Exam Tip: The Texas State Board frequently tests professional boundaries. Always remember: Cosmetologists identify, not diagnose. Refer — don't treat — any infectious, contagious, or inflamed condition.