Anatomy, Physiology, and Disorders of the Hair and Scalp
Hair and follicle anatomy
The hair shaft has three layers: cuticle (outer protective scales), cortex (bulk; keratin, melanin, strength, elasticity), and medulla (central core, often absent in fine hair). The follicle anchors hair; the bulb contains the matrix where cells divide, and the papilla supplies blood and nutrients. Sebaceous glands secrete sebum, which lubricates scalp and hair. The arrector pili muscle causes “goose bumps.”
Growth cycle and scalp disorders
Hair cycles through anagen (active growth, years), catagen (transition, weeks), and telogen (rest and shedding, months). Losing 50–100 hairs daily is normal. Recognize, do not diagnose: seborrheic dermatitis (greasy flakes, redness), psoriasis (thick plaques), tinea capitis (fungal, contagious, broken hairs), folliculitis (infected follicles), pediculosis (lice), alopecia areata (smooth patches), traction alopecia (from tight styles), and trichorrhexis nodosa (node-like breakage).
Worked example
A client has thinning at the temples and tender bumps after tight braids. The culturist identifies likely traction injury, does not apply a medicated treatment or diagnose, loosens the style, avoids tension on the edges, and refers the client to a physician if pain, pus, or hair loss persists. Reasoning: recognizing a disorder is within scope; treating one is not.
Traps
Do not confuse normal shedding with baldness, assume flaking is always dry scalp, or treat contagious fungal or lice conditions. Tight braids are not “normal pain.”