6.1 Hair and Scalp Structure, Composition & Growth Cycles

6.1 Hair and Scalp Structure, Composition & Growth Cycles

Quick Answer: Living hair is produced in the follicle. The dermal papilla feeds the bulb; if that papilla is destroyed, that follicle cannot grow a new hair. The visible shaft is dead keratin with a cuticle, cortex, and sometimes a medulla. Scalp hair typically grows about 0.5 inch per month in textbook tables — treat that as a training average, not an Oklahoma-measured Board figure.

Oklahoma candidates sit a written theory exam that tests hair and scalp structure as scientific concepts, then expects you to use those facts when you consult, cut, color, and decide whether to proceed. Independent OpenExamPrep study for Oklahoma cosmetology treats trichology as working anatomy, not a vocabulary list.

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Root versus shaft

The hair root is the portion of the hair enclosed in the follicle below the epidermis. The hair shaft is the portion that projects above the skin. Chemical waving, relaxing, coloring, and thermal styling act on the shaft you can see, but growth, nutrition, and whether a follicle will ever produce hair again are decided at the root.

A salon example: a client in Edmond wants to know why a burn scar on the scalp stays bald. If the follicle and papilla were destroyed, no product will “wake up” that site. You can style around it; you cannot grow hair from a dead papilla.

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Follicle, bulb, papilla, arrector pili, and sebaceous gland

The follicle is a tube-like depression in the scalp that houses the root. Around it sit the structures NIC-style items love to name:

• Hair bulb — the thickened, club-shaped lower end of the root. Matrix cells in the bulb divide and keratinize to form the hair.
• Dermal papilla (hair papilla) — a cone-shaped elevation of connective tissue that fits into the bulb and carries blood vessels. Nutrients and oxygen arrive here. If the papilla is damaged or destroyed, growth from that follicle is inhibited or permanently lost. That papilla item is a classic written-exam stem: burned, scarred, or surgically removed papilla → no new hair.
• Arrector pili — a small involuntary muscle attached to the follicle. Cold or emotion makes it contract (goosebumps) and can help squeeze sebum toward the surface.
• Sebaceous gland — the oil gland that empties sebum into the follicle. Sebum lubricates the hair and scalp. Overactivity shows as oily scalp; underactivity shows as dry scalp and dry hair. Sebum is not “dirt”; it is the scalp’s lipid film. You manage it with shampoo choice and service frequency, not by stripping it to a squeak on every client.

The follicle also has an inner and outer root sheath. You do not need a histology lecture on exam day, but you do need to know that the living factory is in the bulb/papilla unit, while the shaft you shampoo is already keratinized and biologically dead.

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Cuticle, cortex, medulla

A cross-section of the shaft has up to three layers:

1. Cuticle — the outermost overlapping, scale-like cells pointing toward the distal ends. A compact, intact cuticle looks shiny and resists chemicals. A raised, missing, or cracked cuticle looks dull, tangles, and lets solutions rush into the cortex. Shampoo, pH, and mechanical friction all act first on the cuticle.
2. Cortex — the middle layer and about 90 percent of the hair’s weight. Melanin (eumelanin and pheomelanin) lives here, which is why color and lightener change appearance in the cortex. Tensile strength, elasticity, and the disulfide/hydrogen/salt-bond story of chemical texture services also live here. When a stem asks where melanin or most strength is found, the answer is the cortex, not the cuticle.
3. Medulla — the innermost pith. It may be continuous, fragmented, or absent, especially in fine or naturally very light hair. Missing medulla is not a disease; do not “correct” it.

Keratin is the fibrous protein of hair, skin, and nails. Hair is roughly 90 percent protein. That is why overprocessed hair feels mushy: you have disrupted keratin and bonds in the cortex, not “washed out the vitamins.”

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COHNS elements (conceptual)

Textbook chemistry groups hair’s major elements as COHNS:

• Carbon
• Oxygen
• Hydrogen
• Nitrogen
• Sulfur

Classic training tables put carbon near half of hair’s elemental makeup, with oxygen and nitrogen next, then smaller shares of hydrogen and sulfur. Sulfur matters because disulfide bonds (cystine) are the chemical bonds permanent waves and relaxers target. You are not expected to assay an Oklahoma client’s hair in a lab. You are expected to know which elements show up in the acronym, that hair is a protein, and that sulfur-containing bonds explain why chemical texture services can permanently change shape.

The pie chart in this section uses those typical textbook percentages. They are teaching figures from standard cosmetology chemistry tables, not measurements required or published by the Oklahoma State Board of Cosmetology and Barbering.

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Vellus versus terminal hair

• Vellus hair (sometimes still called lanugo in older fetal context) is short, fine, and usually unpigmented. It often lacks a medulla. You see it on cheeks and in sparse areas of the scalp.
• Terminal hair is longer, coarser, and usually pigmented — scalp, brows, lashes, beard, and the hair you cut and color most days.

Hormones can convert vellus to terminal (or the reverse in miniaturizing androgenetic alopecia). On a consultation, “my hair is getting finer” may be miniaturization, not a shampoo failure. Analysis in Section 6.3 is how you document diameter and density so you do not promise density that biology will not deliver.

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Growth cycles: anagen, catagen, telogen

Each follicle cycles independently, which is why you do not molt like a dog:

After telogen, a new anagen hair can push the club hair out. Normal daily shed is often taught as about 75–100 hairs; a client who brings a photo of a clogged drain is not automatically in crisis, but a sudden clump-shed with a wide part line is a consultation flag (postpartum telogen shift, illness, medication, or traction — covered in 6.2).

Growth rate: many textbooks list scalp hair at about ½ inch (1.25 cm) per month. Use that number when a stem asks for the average rate. Do not treat it as an Oklahoma-measured statistic. Individual rate varies with age, health, season, and location on the head. Eyelashes and body hair have much shorter anagen phases, which is why they never grow to ponytail length.

Exam traps:

• Confusing papilla (blood supply / growth permission) with cuticle (shaft protection).
• Claiming the shaft is alive because it “grows.” Length is added at the bulb; the shaft you hold is dead.
• Calling telogen the growing phase.
• Inventing an Oklahoma Board growth-rate table. Title 175 does not publish a statewide millimeters-per-month standard.

Keep follicle geography mentally mapped: papilla in the bulb, sebum into the follicle, cuticle on the outside of the shaft, cortex where color and strength live. That map is what the written exam and a safe Oklahoma chemical service both require.