2.1 Trichology and Hair Structure

The Oregon Barbering Examination administered by the Oregon Health Licensing Office (HLO) for the Board of Cosmetology is a 100-question, 90-minute theory paper. Anatomy & Physiology is 25 of those items. The largest A&P slice is histology of the hair and scalp — 14 questions covering hair color, diseases and disorders, growth, loss, structure, scalp diseases and disorders, and trichology. HLO draws items from Milady's Standard Professional Barbering, 5th edition (2011), and Pivot Point Barbering Fundamentals, 1st edition (2018), units 102B–109B and 112B. This section is not generic beauty-school filler. It is the map of the protein filament you shampoo, cut, singe, condition, and shave under ORS 690.005(2).

Why trichology is tested in Oregon

Trichology is the scientific study of hair, its diseases, and its care. Oregon tests it because almost every authorized barbering service lands on the same structures. You cannot choose a shampoo for an oily scalp if you cannot name the sebaceous gland. You cannot explain why a razor chatters on a nape if you cannot name the cuticle. You cannot decide when a beard pustule is a stop-and-refer finding if you do not know that every follicle is an opening through the skin. Structure is tool choice and infection control, not decoration on the bulletin.

ORS 690.005(2) defines barbering as cosmetic (not medical) work: shampooing, styling, cutting, singeing, and conditioning the hair; applying hair tonics, dressings, and rinses; massaging the scalp, face, and neck and applying facial and scalp treatments without galvanic or faradic appliances; and shaving, trimming, or cutting the beard or mustache. Every one of those acts assumes you can identify root, shaft, follicle, and shaft layers.

Hair as a keratin appendage

Hair is a slender, threadlike appendage of the skin. It is not a separate organ with its own blood supply along the visible length. Living, dividing cells sit in the hair bulb. After those cells fill with keratin and die, they are pushed upward as the shaft. Standard barbering textbooks state that hair is approximately 90 percent keratin, a hard fibrous protein built from amino acids and cross-linked by disulfide bonds. The remaining fraction is water, lipids, pigment, and trace minerals.

Do not mix two different "90 percent" facts. Hair's chemical bulk is about 90 percent keratin. The structural bulk of a typical strand — about 90 percent of its weight — is the cortex. The cuticle is thin. The medulla may be absent. If an item asks what hair is made of, the answer is keratin. If it asks which layer is most of the strand, the answer is cortex.

Once keratinized, the shaft cannot "heal." Split ends are cut off, not repaired. Conditioners and tonics authorized for Oregon barbers coat and temporarily improve feel; they do not restore a broken cortex.

Hair root versus hair shaft

Divide every strand into two regions:

• The hair root is the portion located below the surface of the epidermis, inside the follicle.
• The hair shaft is the portion that projects above the epidermis — the part you see, comb, clipper, and shave.

The root is not "live hair" in the casual sense. The living factory is the matrix of cells around the dermal papilla. The shaft has no blood supply. That is why Oregon barbers condition and cut the shaft but cannot restore a mechanically destroyed cortex — and why chemical reconstruction is not in barbering scope anyway.

The follicle and its attachments

The hair follicle is a tube-like depression or pocket in the skin or scalp that contains the hair root. Follicles are not perpendicular. They slant. That slant is the grain you read before a razor pass and the direction you comb before a clipper fade.

Structures Oregon candidates must name:

Hair bulb

The lowest, thickened, club-shaped portion of the root. It fits over the dermal papilla like a cup.

Dermal papilla

A small, cone-shaped elevation of dermal connective tissue at the base of the follicle. It carries capillaries and nutrients needed for growth. No papilla, no shaft. Textbook language still calls it the "mother of the hair." Know the function: blood and nerve supply to the bulb.

Arrector pili

A minute involuntary muscle attached to the follicle. Cold or emotion contracts it, lifting the hair (goose bumps) and helping move sebum toward the surface.

Sebaceous gland

An oil gland that empties into the follicle and secretes sebum. Sebum lubricates hair and skin. Overproduction reads as oily scalp; underproduction reads as dry, dull hair. Product choice starts here. Diagnosis of disease does not — barbering is cosmetic.

Follicle wall layers

From the hair outward, name three wall layers:

HLO is not asking you to recite Henle's layer versus Huxley's layer for a barbering certificate. Inner root sheath, outer root sheath, and vitreous membrane are on the structure list.

Shaft layers: cuticle, cortex, medulla

Memorize the pairing the exam loves: porosity is a cuticle property; elasticity is a cortex property. A wet-stretch that returns means the cortex side bonds are still working. A strand that stretches and stays stretched, or snaps, has a compromised cortex. High-porosity cuticles on a nape shave chatter and skip. Low-porosity cuticles shed conditioner and can feel glassy under a clipper.

Infection control at the follicle opening

Every follicle is an ostium — an opening through the epidermis. Bacteria, fungi, and ingrown hairs use that door. Oregon facility rules already require hand washing immediately before and after each client (OAR 817-010-0008) and gloves when routine blood exposure is expected. Structure knowledge tells you why a beard or nape covered with follicular pustules is not a "closer shave" problem. Shaving through folliculitis drives microbes down the follicle. That is a physician referral. You do not lance, squeeze, or disinfect a disease into submission with a razor. Cosmetic practice stops at intact skin.

Oregon shop scenario

A client sits down in a licensed facility in Salem for a skin fade and nape shave before a job interview. The hair feels dry, looks dull, and snags on the comb — high porosity, a cuticle finding. You wet-stretch a strand; it extends and rebounds — elasticity is still acceptable, so clipper and shear tension can be normal. You read the follicle slant on the nape (grain) before lather. At the hairline you see two inflamed follicular pustules. You stop the razor at those openings, finish the cut on intact skin, and refer. Cuticle, cortex, follicle, ostium — that is the 14-question histology block in one service.