Trichology & Hair Analysis

Trichology & Hair Analysis

Trichology is the scientific study of hair, its diseases, and its overall care (derived from the Greek words trichos, meaning hair, and ology, meaning the study of). A professional cosmetologist must be an expert in trichology to analyze hair health, select compatible chemical treatments (such as hair coloring, perming, or relaxing), and identify scalp conditions that require medical referral.

Full human hair structure is divided into two primary parts:

1. Hair Root: The portion of hair located beneath the surface of the epidermal skin.
2. Hair Shaft: The non-living portion of hair that projects above the skin surface.

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Structures of the Hair Root

Five key structures form the hair root assembly within the dermis:

• Hair Follicle: The 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 grows out at an incline.
• Hair Bulb: The lowest area of the hair strand; a thickened, club-shaped structure that forms the lower part of the hair root and fits over the dermal papilla.
• Dermal Papilla: A small, cone-shaped elevation located at the base of the hair follicle that fits into the hair bulb. It contains the blood and nerve supply that provides nutrients needed for hair growth.
• Arrector Pili Muscle: The minute, involuntary smooth muscle in the base of the hair follicle. Cold temperature or emotional fear contracts this muscle, pulling the hair follicle upright and causing goosebumps.
• Sebaceous Glands: Oil glands connected to hair follicles that secrete sebum, a fatty substance that lubricates the hair shaft and skin.

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Histology of the Hair Shaft

The hair shaft consists of three distinct microscopic layers:

1. Cuticle: The outermost layer of the hair shaft. It consists of a single, overlapping layer of transparent, scale-like cells resembling shingles on a roof. The cuticle protects the inner cortex and creates shine. A healthy, closed cuticle lays flat, preventing excessive moisture loss and resisting chemical penetration.
2. Cortex: The middle, fibrous layer of the hair shaft, making up roughly 90% of the total hair weight. The cortex is composed of elongated polypeptide chains of keratin protein. It houses natural melanin pigment and determines the hair's elasticity, tensile strength, and chemical processing capacity.
3. Medulla: The innermost core of the hair strand, composed of round cells. Often referred to as the pith or core. Fine hair and naturally blonde hair frequently lack a medulla, whereas coarse hair almost always contains one. The medulla plays no active role in salon chemical services.

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Chemical Composition & Side Bonds of Hair

Hair protein is made of long chains of amino acids linked together by peptide bonds to form keratin. The elemental composition of human hair is summarized by the acronym COHNS:

• Carbon (C): 51%
• Oxygen (O): 21%
• Nitrogen (N): 17%
• Hydrogen (H): 6%
• Sulfur (S): 5%

Side Bonds of the Cortex

The cortex's polypeptide chains are cross-linked laterally by three types of side bonds that account for hair's strength and elasticity:

1. Hydrogen Bonds: Physical side bonds broken by water or heat. They are weak individually but numerous, accounting for one-third of the hair's overall strength. Hydrogen bonds reform as the hair cools or dries during wet-setting or heat styling.
2. Salt Bonds: Physical side bonds formed between positive and negative charges of amino acid chains. They are broken by strong acidic or alkaline pH solutions and account for one-third of hair strength.
3. Disulfide Bonds: Strong chemical side bonds formed when sulfur atoms in adjacent cysteine amino acids join together. Disulfide bonds cannot be broken by water or heat; they require chemical reducing agents (such as perming lotions or relaxers) to break. Re-forming disulfide bonds with neutralizers establishes permanent hair restyling.

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The Hair Growth Cycle

Hair follicles undergo cyclical growth, regression, and rest:

• Anagen Phase (Active Growth): The phase of active cell division in the matrix bulb. Hair grows at an average rate of 0.5 inches (1.25 cm) per month. Lasts between 3 to 5 years (up to 7 years on some individuals). Approximately 85-90% of scalp hair is in anagen at any given time.
• Catagen Phase (Transition): The brief regressive phase where the hair bulb detaches from the dermal papilla, forming a club hair. Follicle canal shrinks. Lasts 1 to 2 weeks.
• Telogen Phase (Resting/Shedding): The final resting phase where the fully formed club hair remains in place until shed or pushed out by new anagen growth. Lasts 3 to 6 months. Normal daily shedding ranges from 50 to 100 hairs per day.

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Pre-Service Hair Analysis

Before performing any hair service, the cosmetologist must conduct a hair analysis evaluating five key parameters:

1. Texture: The diameter of an individual hair strand. Categorized as coarse (largest diameter, resistant to chemicals), medium (standard baseline), or fine (smallest diameter, processes quickly).
2. Density: The number of individual hair strands per square inch of scalp. Classified as thin (low), medium, or thick (high density). Average scalp contains approximately 100,000 to 150,000 hairs.
3. Porosity: The ability of hair to absorb moisture, directly related to cuticle scale condition:
   • Low Porosity: Resistant cuticle, requires longer processing or alkaline solutions.
   • Average Porosity: Normal hair, processes predictably.
   • High Porosity: Lifted/damaged cuticle, absorbs liquid rapidly but fades quickly; requires gentle, low-pH solutions.
4. Elasticity: The ability of hair to stretch and return to its original length without breaking. Healthy wet hair stretches up to 50% of its length without breaking; dry hair stretches 20%. Low elasticity indicates damaged cortex side bonds.
5. Growth Patterns: Direction of hair emerging from scalp. Includes whorl (circular growth pattern at crown), cowlick (tuft of hair standing straight up), and hair stream (hair flowing in the same direction).

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Scalp and Hair Disorders

• Alopecia: Abnormal hair loss (Androgenetic alopecia, Alopecia areata, Alopecia universalis).
• Pityriasis: Technical term for dandruff. Pityriasis capitis (classic dry dandruff) vs. Pityriasis steatoides (severe oily, crusty dandruff).
• Tinea: Technical term for ringworm; fungal infection. Tinea capitis causes red papules at scalp follicle openings.
• Pediculosis Capitis: Infestation of the hair and scalp with head lice.
• Scabies: Contagious skin disease caused by the itch mite burrowing under skin.

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Hair Component & Bond Comparison