4.1 Hair Structure, Composition & Growth Cycle

4.1 Hair Structure, Composition & Growth Cycle

Quick Answer: Hair is mostly keratin protein. The visible shaft has cuticle, cortex, and (often) medulla layers; the living root sits in a follicle fed by the papilla. Hair grows in anagen → catagen → telogen cycles. Porosity, texture, elasticity, and density tell you how that hair will cut, style, and respond to products—core Scientific Concepts material on the NIC Barber 1 (No Chemical Services) exam Georgia Barber II candidates take.

Trichology—the study of hair and scalp—is not optional trivia for Barber II. Every haircut, shampoo, and scalp consultation depends on knowing what you are touching and whether it is safe to proceed. Georgia’s public-protection model expects you to recognize normal structure and growth so you can choose techniques wisely and refuse service when the scalp or hair signals a contagious problem (covered in the next section).

The Hair Shaft: Three Layers

The hair shaft is the portion above the skin surface. It is technically non-living keratinized tissue—no blood supply—but its layers still control shine, strength, and how products behave.

• Cuticle — outermost layer of overlapping transparent scales, arranged like shingles on a roof, pointing toward the ends. When scales lie flat, hair looks shiny and feels smooth; when raised, hair feels rough, tangles, and looks dull. Alkaline products tend to lift the cuticle; acid-balanced products help it lie flat again.
• Cortex — middle layer making up about 90% of the hair’s weight. It contains the melanin pigment that gives natural color and the polypeptide chains and side bonds that give hair its strength and shape. Even though Barber II does not perform chemical texture or color services, you still need cortex facts for exam items and for understanding why damaged hair behaves differently under clippers and shears.
• Medulla — innermost core of soft, loosely arranged cells. It may be continuous, interrupted, or absent—especially in fine or very light hair. Presence or absence of a medulla is normal anatomy, not a disorder.

Root Structures Below the Skin

Living growth happens below the surface inside the follicle—a tube-like depression in the skin.

• Hair follicle — the pocket that houses the root; scalp follicles are typically denser and differently angled than facial follicles, which matters for beard design and grain direction when shaving.
• Hair bulb — the thickened, club-shaped lower end of the strand that fits over the papilla.
• Dermal papilla — a cone-shaped elevation at the follicle base with blood vessels and nerves that nourish growing cells. Permanent destruction of the papilla stops growth in that follicle.
• Sebaceous gland — oil gland attached to the follicle that secretes sebum, which lubricates hair and skin. Excess sebum contributes to oily scalp; underproduction contributes to dryness.
• Arrector pili muscle — tiny involuntary muscle attached to the follicle; contraction causes goose bumps and helps push sebum toward the surface.

Composition: Keratin and Bonds (Exam Context)

Hair is roughly 90% protein (keratin). Amino acids link into polypeptide chains. Side bonds between chains include:

• Hydrogen bonds and salt bonds — relatively weak; broken by water or heat and reform as hair dries or cools. These explain wet setting, blow-drying, and thermal styling behavior within Barber II scope.
• Disulfide bonds — stronger sulfur-to-sulfur links. Water and ordinary heat do not break them; chemical waving and relaxing solutions do. Barber II licensees do not perform those chemical texture services in Georgia—that is Master Barber territory—but NIC theory still expects you to know which bond type each process affects.

Hair Properties You Must Assess

Before cutting or shampooing, evaluate these four properties:

1. Porosity — ability to absorb moisture. Low porosity (tight cuticle) resists absorption; high porosity (raised or damaged cuticle) absorbs quickly and can feel rough when you slide fingers from ends toward the scalp against the scale direction.
2. Texture — diameter of the individual strand: fine, medium, or coarse. Texture is not the same as density.
3. Elasticity — ability to stretch and return without breaking. Healthy wet hair can stretch roughly 40–50% of its length; poor elasticity signals damage and breakage risk during combing or tension cutting.
4. Density — number of hairs per square inch. High density needs more sectioning and may require different clipper work than sparse hair on the same head shape.

Wave pattern (straight, wavy, curly, coily) is determined largely by follicle shape and cortex structure. Cutting with or against the growth pattern changes how the finished style sits.

The Growth Cycle: Anagen, Catagen, Telogen

Scalp hair does not grow continuously in one long push. Each follicle cycles independently:

Average scalp growth is roughly ½ inch (1.25 cm) per month, though genetics, health, and age change that. Facial hair cycles differ in timing from scalp hair—useful context when clients ask why beard and scalp growth feel “out of sync.”

Normal daily shed of about 50–100 hairs can be telogen hairs releasing. Sudden excessive shed, patchy loss, or scarring alopecia is not “just a haircut problem”—adapt the service and suggest medical evaluation when appropriate.

Hair Loss Types — Recognition Overview

Barbers do not diagnose medical alopecia, but the exam and shop practice expect recognition language:

• Androgenic (androgenetic) alopecia — most common pattern baldness; male pattern often shows frontotemporal recession and crown thinning.
• Alopecia areata — sudden smooth, round bald patches; autoimmune; non-contagious; style around patches and refer for medical care.
• Telogen effluvium — temporary diffuse shedding after stress, illness, or hormonal change.
• Traction alopecia — loss from chronic tight tension (tight styles, aggressive pulling).
• Alopecia totalis / universalis — broader loss of scalp or body hair (medical referral).

When loss is present, consult on realistic styles, avoid promising medical results, and never claim to “cure” baldness with a cut alone.

Why This Matters for Barber II

Understanding structure and cycle lets you explain porosity-related product choices, cut with growth patterns, set client expectations about shed and regrowth, and document observations that may require referral. Scientific Concepts is about 30% of the NIC Barber 1 theory outline—hair anatomy and growth are high-yield facts inside that domain.