4.2 Hair Growth Cycles, Analysis & Scalp Disorders

4.2 Hair Growth Cycles, Analysis & Scalp Disorders

A comprehensive, systematic analysis of the hair and scalp is mandatory prior to performing any professional salon service. Evaluating hair porosity, elasticity, density, texture, and scalp health ensures that haircutting, coloring, and chemical texturizing services are selected safely. Furthermore, pre-service analysis enables cosmetologists to detect contagious fungal, parasitic, or bacterial conditions that mandate immediate service refusal.

The Three Phases of the Hair Growth Cycle

Hair growth does not occur continuously; rather, each individual hair follicle cycles independently through three repeating biological phases: anagen, catagen, and telogen.

1. Anagen Phase (Active Growth Phase)

During the anagen phase, matrix cells in the hair bulb divide rapidly around the dermal papilla, forming new hair fibers that are pushed upward and keratinized as they mature.

• Duration: Lasts between 2 to 6 years (occasionally up to 7 years in individuals with extended growth cycles).
• Proportion: At any given time, approximately 85% to 90% of all scalp hair is actively growing in the anagen phase.
• Growth Rate: Scalp hair grows at an average rate of 0.5 inches (1.25 cm) per month (approximately 6 inches per year). Growth rate peaks between the ages of 15 and 30.

2. Catagen Phase (Transitional Phase)

The catagen phase signals the end of active hair growth and represents the transitional period between growth and resting.

• Physiology: The hair follicle shrinks, the lower root detaches from the dermal papilla, and the follicle base contracts. The hair bulb shrinks into a rounded "club hair."
• Duration: Lasts 1 to 2 weeks.
• Proportion: Less than 1% of scalp hair is in the catagen phase at any single moment.

3. Telogen Phase (Resting & Shedding Phase)

The telogen phase is the final resting stage of the hair growth cycle.

• Physiology: The fully formed club hair rests in the follicle until it is pushed out by a new anagen hair or falls out during normal brushing, washing, or combing.
• Duration: Lasts approximately 3 to 6 months (average 100 days).
• Proportion: Approximately 10% to 15% of scalp hair is in the telogen phase simultaneously.
• Physiological Shedding Rate: A healthy scalp naturally sheds 50 to 100 hairs per day. Shedding within this range represents normal physiological replacement.

The Four Key Factors of Professional Hair Analysis

Before selecting chemical formulations or cutting tools, the cosmetologist must evaluate four physical properties:

Non-Contagious Scalp and Hair Shaft Disorders

Pityriasis (Dandruff)

Dandruff is characterized by excessive shedding of epidermal scalp cells, caused by an overgrowth of a naturally occurring fungus called Malassezia (a lipophilic yeast).

1. Pityriasis Capitis (Classic Dry Dandruff): Small, white, dry scalp flakes accompanied by mild itching. Treated with over-the-counter anti-dandruff shampoos containing zinc pyrithione, selenium sulfide, or ketoconazole.
2. Pityriasis Steatoides (Greasy/Waxy Dandruff): Severe form characterized by oily, yellowish crusts mixed with sebum on the scalp. If severely inflamed or oozing, refer client to a physician.

Structural Defects of the Hair Shaft

• Trichoptilosis (Split Ends): Vertical splitting of hair fibers at the distal end caused by mechanical stress, heat, or chemical over-processing. The only true remedy is trimming the damaged ends.
• Trichorrhexis Nodosa (Knotted Hair): Swollen nodules along the hair shaft where the cuticle layer has eroded, exposing cortical fibers. Hair breaks easily at these points.
• Monilethrix (Beaded Hair): Genetic condition with alternating constricted and swollen beaded segments along the hair shaft. Hair is extremely brittle.
• Fragilitas Crinium (Brittle Hair): Technical term for brittle hair that splits anywhere along its length.
• Canities: Technical term for gray hair resulting from loss of melanin in the cortex. Congenital canities exists at birth (albinism); acquired canities develops with age or genetics.
• Hypertrichosis (Hirsutism): Abnormal terminal hair growth in body areas that normally grow only fine vellus hair.

Contagious Scalp Disorders & Parasitic Infestations

When a client exhibits symptoms of a contagious fungal infection, parasitic infestation, or bacterial outbreak, the cosmetologist must immediately decline service and advise the client to consult a physician.

Fungal Infections (Tinea)

Tinea is the technical term for ringworm, a contagious fungal infection caused by dermatophyte organisms:

• Tinea Capitis (Scalp Ringworm): Red papules at follicle openings; hair shafts become brittle and break off at scalp level, leaving small black dots and bald patches.
• Tinea Favosa (Favus): Severe fungal infection featuring dry, sulfur-yellow, cup-like crusts on the scalp called scatula. Favus crusts emit a distinctive musty odor and can cause permanent scarring alopecia.

Parasitic Infestations

• Pediculosis Capitis (Head Lice): Contagious infestation of head lice (Pediculus humanus capitis). Symptoms include intense scalp itching and visible oval white/translucent egg sacs called nits glued firmly to the hair shaft within 1/4 inch of the scalp. Unlike dandruff, nits cannot be brushed off.
• Scabies: Highly contagious disease caused by the itch mite (Sarcoptes scabiei), which burrows under skin to lay eggs. Causes intense itching and red vesicles/burrow lines.

Bacterial Infections (Staphylococci)

• Folliculitis: Inflammation of hair follicles presenting as small pus-filled bumps (pustules).
• Furuncle (Boil): Acute, localized staphylococcal infection of a single hair follicle causing severe pain and pus.
• Carbuncle: Large cluster of interconnected furuncles involving multiple hair follicles.

Washington State Decontamination & Sanitation Mandates (WAC 308-20)

Under Washington State law, cosmetologists are legally prohibited from diagnosing medical conditions or treating contagious diseases.

If a contagious disorder is identified during pre-service scalp inspection:

1. Politely Decline Service: Explain calmly in private that a scalp irregularity prevents service completion.
2. Refer to Physician: Recommend medical evaluation by a licensed physician or dermatologist.
3. Decontaminate Tools & Workstation: Isolate all tools, capes, and towels used on the client.
4. Disinfect Non-Porous Tools: Wash non-porous tools with soap and water, then fully immerse in an EPA-registered, hospital-grade disinfectant (bactericidal, virucidal, fungicidal) for the required contact time (10 minutes).
5. Launder Linens: Wash towels and cloth capes in hot water at >140°F (60°C) with detergent and bleach.