Overview
This study guide covers the essential hair and scalp science concepts tested on the Barber License Exam. Topics include the physical structure of hair, its chemical composition and bonds, the hair growth cycle, and common scalp conditions and disorders. Mastering these concepts is critical for both the written exam and safe, professional practice in the barbershop.
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Hair Structure
Key Concepts
The hair strand is divided into two main divisions: the hair root (below the skin surface) and the hair shaft (above the skin surface). The shaft itself is composed of three concentric layers, each with a distinct role.
The Three Layers of the Hair Shaft
| Layer | Position | Function |
|-------|----------|----------|
| Cuticle | Outermost | Overlapping scale-like cells that protect inner layers |
| Cortex | Middle | Contains melanin pigment; makes up the majority of hair's bulk |
| Medulla | Innermost | Soft, loosely connected cells and air spaces; not always present |
Structures of the Hair Root
• Hair follicle – The tube-like structure in the skin (extending into the dermis) that surrounds and supports the hair root
• Hair bulb – The thickened, club-shaped lower portion of the hair root that encases the dermal papilla
• Hair papilla – The small, cone-shaped elevation at the base of the follicle; contains blood vessels that supply nutrients for hair growth
• Arrector pili muscle – A tiny muscle attached to the follicle; contracts to make hair stand erect (goosebumps)
• Sebaceous gland – An oil gland attached to the follicle that secretes sebum, lubricating and protecting hair and skin
Key Terms
• Cuticle – Protective outer layer of scale-like cells
• Cortex – Middle layer; site of pigment and most structural proteins
• Medulla – Innermost, sometimes absent core layer
• Hair follicle – Skin structure housing the hair root
• Hair papilla – Nutrient-supplying base of the follicle
• Arrector pili – Muscle responsible for "goosebumps"
• Sebum – Natural oil secreted by sebaceous glands
⚠️ Watch Out For
• Don't confuse the hair bulb (structural base of the root) with the hair papilla (the vascular elevation inside the bulb). The papilla feeds the bulb; the bulb encases the papilla.
• The medulla is not always present — its absence does not indicate unhealthy hair.
• The cuticle protects the hair but does not contain pigment — pigment is exclusively in the cortex.
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Chemical Composition
Key Concepts
Hair is approximately 97% keratin, a fibrous protein built from amino acids. The structural integrity and shape of hair depend on several types of chemical bonds within and between protein chains in the cortex. Two types of melanin determine natural hair color.
Hair's Primary Protein
• Keratin – The dominant fibrous protein of hair, formed from amino acids
• Sulfur – Found in high concentration in the amino acid cysteine; gives hair much of its strength through disulfide bonds
The Three Major Chemical Bonds
| Bond Type | Strength | What Breaks It | How It's Used |
|-----------|----------|----------------|---------------|
| Hydrogen bonds | Weak (but numerous) | Water and heat | Temporary styling (wet sets, blow-drying); re-forms as hair dries |
| Disulfide bonds | Strong | Permanent wave lotion (chemical reduction) | Perms — broken by waving lotion, re-formed by neutralizer |
| Salt bonds | Moderate | Strong acids or alkaline solutions | Broken by pH extremes |
Hair Color Pigments
• Eumelanin – Dark melanin; responsible for black and brown hair colors
• Pheomelanin – Lighter, diffuse melanin; responsible for red, auburn, and yellow tones
• Both pigments are produced by melanocytes located in the hair follicle
• The ratio of eumelanin to pheomelanin determines a person's natural hair color
Key Terms
• Keratin – Primary structural protein of hair
• Disulfide bonds – Strong bonds broken/re-formed during permanent waving
• Hydrogen bonds – Weak bonds responsible for temporary style changes
• Salt bonds – Ionic bonds broken by pH extremes
• Eumelanin – Dark pigment (black/brown)
• Pheomelanin – Light pigment (red/yellow)
• Melanocytes – Pigment-producing cells in the follicle
⚠️ Watch Out For
• Hydrogen bonds = temporary changes (blow-dry, wet set). Disulfide bonds = permanent changes (perms). This distinction is a frequent exam question.
• Remember the perm sequence: waving lotion breaks disulfide bonds → hair is reshaped → neutralizer re-forms them. Getting the order wrong is a common mistake.
• Salt bonds are broken by pH extremes (both acid and alkaline), not by heat or water — don't confuse them with hydrogen bonds.
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Hair Growth Cycle
Key Concepts
All hair goes through a continuous, three-phase growth cycle. The phases determine how long hair grows, when it transitions, and when it sheds. Understanding this cycle is essential for diagnosing hair loss and setting client expectations.
The Three Phases
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ANAGEN → CATAGEN → TELOGEN → (back to ANAGEN)
(Growth) (Transition) (Resting/Shedding)
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| Phase | Also Called | Duration | What Happens |
|-------|-------------|----------|--------------|
| Anagen | Growth phase | 2–7 years | Hair actively grows; determines maximum hair length |
| Catagen | Transition phase | 2–3 weeks | Follicle shrinks and detaches from dermal papilla |
| Telogen | Resting/Shedding phase | 3–4 months | Hair rests, then is shed; cycle restarts |
Normal Growth Statistics
• Average daily shedding: 50–100 hairs per day (normal range)
• Average monthly growth: approximately ½ inch (1.25 cm) per month
• Growth rates are influenced by age, health, genetics, and nutrition
Key Terms
• Anagen – Active growth phase
• Catagen – Brief transitional/shrinking phase
• Telogen – Resting and shedding phase
• Dermal papilla – Detaches from follicle during catagen
⚠️ Watch Out For
• The anagen phase determines how long hair can grow — longer anagen = longer potential hair length. This is a classic exam question.
• Know the correct order: Anagen → Catagen → Telogen. Mixing up catagen and telogen is a common error.
• Shedding 50–100 hairs/day is normal — don't confuse normal shedding with pathological hair loss.
• The catagen phase is very brief (weeks), while telogen lasts months.
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Scalp Conditions & Disorders
Key Concepts
Barbers must be able to identify scalp conditions to determine whether a service can safely proceed or whether the client must be referred to a physician. Contagious conditions must never be treated in the barbershop.
Dandruff (Pityriasis)
| Type | Characteristics |
|------|----------------|
| Pityriasis capitis simplex | Dry dandruff; small, white, loose flakes |
| Pityriasis steatoides | Oily/waxy dandruff; flakes stick to the scalp and hair shaft |
• General term: Pityriasis – excessive shedding of dead skin cells from the scalp
• Seborrhea – a related condition of excessive sebum (oil) secretion from sebaceous glands; can lead to oily scalp, dandruff, and scalp inflammation
Hair Loss Conditions (Alopecia)
| Condition | Cause | Characteristics |
|-----------|-------|----------------|
| Alopecia areata | Autoimmune | Sudden hair loss in round or irregular patches |
| Androgenic alopecia | Hereditary; DHT | Pattern baldness; follicles shrink over time due to dihydrotestosterone (DHT) |
Contagious Scalp Conditions
• Tinea capitis – Fungal infection of the scalp (ringworm of the scalp)
- Highly contagious
- Must NOT be treated in the barbershop
- Client must be referred to a physician
Key Terms
• Pityriasis – Technical term for dandruff
• Pityriasis capitis simplex – Dry dandruff
• Pityriasis steatoides – Oily/waxy dandruff
• Tinea capitis – Fungal scalp infection (ringworm); contagious
• Alopecia areata – Autoimmune patchy hair loss
• Androgenic alopecia – Hereditary pattern baldness
• DHT (dihydrotestosterone) – Hormone that shrinks follicles in pattern baldness
• Seborrhea – Excessive oil secretion from sebaceous glands
• Sebaceous gland – Oil gland attached to the hair follicle
⚠️ Watch Out For
• Tinea capitis is contagious — you must know to refuse service and refer the client. Treating it in the shop is a serious exam and real-world error.
• Know the difference between the two dandruff types: simplex = dry/flaky, steatoides = oily/sticky.
• Alopecia areata ≠ androgenic alopecia: areata is autoimmune and patchy; androgenic is hereditary and patterned.
• DHT is the specific hormone linked to androgenic alopecia — not testosterone directly, but its derivative.
• Seborrhea (excess oil) is different from pityriasis (excess skin shedding), but the two often occur together.
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Quick Review Checklist
Use this checklist to confirm you're exam-ready:
Hair Structure
• [ ] Name and describe the three layers of the hair shaft (cuticle, cortex, medulla)
• [ ] Identify the two main divisions of a hair strand (root vs. shaft)
• [ ] Explain the role of the hair papilla, hair bulb, and hair follicle
• [ ] Describe the function of the arrector pili muscle and sebaceous gland
Chemical Composition
• [ ] State that hair is ~97% keratin
• [ ] Explain the role of sulfur and cysteine in hair strength
• [ ] Distinguish between hydrogen bonds (temporary/heat & water), disulfide bonds (permanent/chemical), and salt bonds (pH)
• [ ] Describe the perm process in terms of bond breaking and re-forming
• [ ] Differentiate eumelanin (black/brown) from pheomelanin (red/yellow)
Hair Growth Cycle
• [ ] Recite the three phases in order: Anagen → Catagen → Telogen
• [ ] State the duration of each phase
• [ ] Know normal daily shedding (50–100 hairs) and monthly growth (~½ inch)
Scalp Conditions
• [ ] Define pityriasis and distinguish simplex (dry) from steatoides (oily)
• [ ] Identify tinea capitis as a contagious fungal condition requiring physician referral
• [ ] Differentiate alopecia areata (autoimmune, patchy) from androgenic alopecia (hereditary, DHT-related)
• [ ] Explain the role of sebaceous glands and seborrhea in scalp health
• [ ] Know which conditions are contraindicated for barbershop services
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Good luck on your Barber License Exam! Review these concepts regularly, and always connect the science back to safe, professional client care.