3.1 Hair and Scalp Analysis & Disorders
Key Takeaways
- The hair shaft comprises three layers: cuticle (outer protective layer of scale-like cells), cortex (middle layer containing 90% of weight, melanin, and elasticity), and medulla (innermost core, often absent in fine hair).
- Hair grows in three distinct phases: Anagen (active growth stage lasting 2-6 years), Catagen (brief transition stage lasting 1-2 weeks), and Telogen (resting stage lasting 3-6 months).
- Hair analysis evaluates four primary characteristics: porosity (ability to absorb moisture), elasticity (ability to stretch and return without breaking), density (number of hairs per square inch), and texture (diameter of individual hair strands).
- Contagious scalp conditions such as tinea (ringworm) and pediculosis capitis (head lice) strictly prohibit salon chemical or styling services until cleared by a physician.
Hair and Scalp Analysis & Disorders
Proper hair and scalp analysis is the foundation of safe and effective cosmetology practice. Understanding hair histology, growth cycles, physical characteristics, and scalp pathologies ensures the cosmetologist selects the appropriate chemical services, treatments, and safety precautions.
Hair Shaft Structure & Follicle Anatomy
A single hair strand is divided into two primary divisions: the hair root (located beneath the skin surface within the hair follicle) and the hair shaft (the non-living, keratinized portion extending above the skin surface).
The Three Layers of the Hair Shaft
| Layer | Description & Function | Key Features |
|---|---|---|
| Cuticle | Outermost layer consisting of transparent, scale-like overlapping cells pointing toward the hair ends. | Protects the inner cortex. Controls porosity and moisture absorption. Acidic solutions seal the cuticle; alkaline solutions open scales. |
| Cortex | Fibrous middle layer formed by elongated protein cells; accounts for ~90% of total hair weight. | Contains natural melanin pigment (eumelanin and pheomelanin), polypeptide chains, and chemical cross-links (hydrogen, salt, disulfide bonds). Gives hair strength and elasticity. |
| Medulla | Innermost core composed of round cells and air spaces. | Often absent in fine or naturally blond hair. Does not participate in chemical hair processing. |
Key Structures of the Hair Root
- Hair Follicle: A tube-like depression or pocket in the skin or scalp that contains the hair root. Follicles extend down into the dermis and are angled so hair flows to one side.
- Hair Bulb: The lowest area of the hair strand—a thickened, club-shaped structure that fits over and protects the dermal papilla.
- Dermal Papilla: A small cone-shaped elevation located at the base of the hair follicle. It contains the blood and nerve supply that provides vital nourishment for hair growth.
- Arrector Pili Muscle: A tiny, involuntary smooth muscle attached to the base of the hair follicle. Cold temperature or fear causes it to contract, pulling the hair upright and producing "goosebumps."
- Sebaceous Glands: Sac-like oil glands connected to the hair follicle that secrete sebum, a natural lipid substance that lubricates the skin and hair shaft.
The Hair Growth Cycle
Hair does not grow continuously; instead, each hair follicle undergoes a repeating pattern of growth, involution, and rest consisting of three distinct phases.
┌────────────────────────────────────────┐
│ ANAGEN PHASE │
│ Active Growth (2-6 Years / ~90% hair) │
└──────────────────┬─────────────────────┘
│
▼
┌────────────────────────────────────────┐
│ CATAGEN PHASE │
│ Transition Stage (1-2 Weeks / <1%) │
└──────────────────┬─────────────────────┘
│
▼
┌────────────────────────────────────────┐
│ TELOGEN PHASE │
│ Resting/Shedding (3-6 Months / 10-15%)│
└────────────────────────────────────────┘
Growth Phase Details
- Anagen Phase (Growth Stage): The period of active hair follicle proliferation. New hair cells are produced in the matrix around the dermal papilla and pushed upward to keratinize. Hair grows at an average rate of 0.5 inches (1.25 cm) per month. Anagen lasts between 2 to 6 years, and approximately 85% to 90% of scalp hair is in this phase at any given time.
- Catagen Phase (Transition Stage): A brief transitional phase marking the end of active hair production. The follicle canal shrinks, the hair bulb detaches from the dermal papilla, and the base of the hair strand forms a hard club hair. Catagen lasts 1 to 2 weeks, accounting for less than 1% of scalp hair.
- Telogen Phase (Resting Stage): The final resting phase of the cycle. The club hair remains in the follicle until it is shed or pushed out by a new growing anagen hair. Telogen lasts 3 to 6 months (approx. 100 days), comprising 10% to 15% of scalp hair. Normal shedding ranges from 50 to 100 hairs per day.
Hair Analysis: Porosity, Elasticity, Density & Texture
Before performing any chemical service (coloring, perming, relaxing), the cosmetologist must systematically evaluate four key physical characteristics.
1. Porosity
Porosity is the hair's ability to absorb moisture. It is determined by the condition of the cuticle layer.
- Low Porosity: Cuticle scales lie flat, tight, and compact. Hair is hydrophobic and resistant to chemical penetration. Requires higher alkalinity or heat to open the cuticle.
- Normal (Average) Porosity: Cuticle scales are slightly raised. Hair absorbs and retains moisture predictably during chemical processing.
- High Porosity: Cuticle scales are raised, damaged, or missing due to over-processing, heat, or environmental damage. Hair absorbs moisture quickly but loses it just as fast. Requires lower pH chemical products to avoid severe damage.
2. Elasticity
Elasticity is the hair's ability to stretch and return to its original length without breaking. It directly reflects the structural integrity of the cortex's disulfide bonds.
- Normal Elasticity: Wet hair with normal elasticity can stretch up to 50% of its original length and spring back without breaking. Dry hair stretches up to 20%.
- Low Elasticity: Hair is brittle, breaks easily under tension, and fails to return to its original length. Chemical services are contraindicated until hair strength is restored with protein and conditioning treatments.
3. Density
Density refers to the number of individual hair strands per square inch (2.5 sq cm) of scalp area. It is categorized as low (thin), medium (average), or high (thick/dense).
- Average scalp density is approximately 2,200 hairs per square inch, totaling roughly 100,000 individual hairs on the head.
- Hair density varies by natural hair color: Blonds average ~140,000 hairs; Brown/Black hair averages ~110,000 hairs; Redheads average ~80,000 hairs.
4. Texture
Texture describes the diameter of an individual hair strand. It is classified into three categories:
- Coarse Hair: Has the largest diameter and strongest cortex. Requires higher chemical concentration and longer processing times.
- Medium Hair: Average strand diameter. Standard baseline for chemical processing.
- Fine Hair: Smallest diameter and fragile cortex. Highly susceptible to chemical over-processing and heat damage.
Scalp Disorders, Infections & Alopecia
Cosmetologists must differentiate non-contagious scalp conditions from contagious infections and hair loss disorders.
Scalp Disorders & Dandruff
- Pityriasis (Dandruff): Excessive shedding of epidermal scalp cells, caused by an overgrowth of the fungus Malassezia.
- Pityriasis Capitis Simplex: Classic dry dandruff characterized by scalp irritation, itching, and small white scales.
- Pityriasis Steatoides: Severe greasy dandruff characterized by an accumulation of waxy, yellowish scales mixed with sebum. Note: Chemical services must be postponed if scalp inflammation, redness, or open sores are present.
Contagious Diseases (STRICT CONTRAINDICATIONS - DO NOT SERVICE)
| Disease | Cause | Clinical Presentation |
|---|---|---|
| Tinea Capitis | Fungal infection (Ringworm) | Red papules or spots at follicle openings; hair breaks off leaving stubble. |
| Tinea Favosa | Fungal infection | Dry, sulfur-yellow, cup-like crusts called scutula with a musty odor. |
| Pediculosis Capitis | Parasitic head lice infestation | Intense scalp itching; visible insects and tiny oval white eggs (nits) glued to hair shafts. |
| Scabies | Contagious itch mite (Sarcoptes scabiei) | Mites burrow under skin causing violent itching, vesicles, and pustules. |
Types of Alopecia (Abnormal Hair Loss)
- Androgenetic Alopecia: Progressive hair thinning caused by androgenic hormones (dihydrotestosterone / DHT) converting terminal hair into fine vellus hair. Follows pattern baldness in men and diffuse thinning in women.
- Alopecia Areata: Autoimmune disorder causing round, smooth, bald patches on the scalp or body.
- Telogen Effluvium: Rapid premature shedding of hairs in the telogen phase, triggered by severe physiological or emotional stress, fever, childbirth, or shock.
- Cicatricial (Scarring) Alopecia: Permanent hair loss resulting from inflammation and scarring that destroys the hair follicle structure.
Which layer of the hair shaft contains the melanin pigments that give hair its natural color and accounts for approximately 90 percent of the hair's total weight?
During which phase of the hair growth cycle does the hair follicle actively produce new hair cells, lasting anywhere from two to six years?
A client presents with severe scalp itching and yellowish, waxy crusts mixed with greasy scales. Which scalp disorder is indicated, and how should the cosmetologist proceed?