Hair and Scalp Anatomy, Disorders, and Diseases
Hair and scalp anatomy, disorders, and diseases
This domain tests the structure of hair and scalp, the hair-growth cycle, and the barber's legal and safety boundary: recognize common conditions, do not diagnose or treat disease, and refer when a service is contraindicated.
Hair structure
- The hair shaft has three layers: the cuticle (protective outer scales), cortex (bulk of the fiber, containing melanin), and medulla (central core, sometimes absent).
- The follicle is a tube in the skin. At its base, the bulb surrounds the papilla, which supplies blood and nerves; matrix cells divide to build the hair.
- Sebaceous glands secrete sebum into the follicle; the arrector pili muscle contracts in cold or emotion and causes goose bumps.
- Melanin determines color: eumelanin gives brown or black, pheomelanin gives red or yellow. Gray hair has reduced melanin, not white pigment.
Growth and hair types
- Anagen is the active growth phase (roughly 2-7 years), catagen is transition (weeks), and telogen is resting and shedding (about 3 months). Shedding 50-100 hairs daily is normal.
- Lanugo is fine fetal hair; vellus is short, fine body hair; terminal hair is longer, coarser, and pigmented.
- Texture, density, porosity, and elasticity guide product choice and chemical service decisions.
Disorders and diseases
- Contagious conditions include tinea capitis (fungal ringworm), pediculosis (lice), scabies, and impetigo. Do not service; refer and disinfect.
- Noncontagious problems include seborrheic dermatitis, psoriasis, alopecia areata, traction alopecia, folliculitis, furuncles, and carbuncles. Inflamed or broken skin is a service contraindication.
- Barbers may recognize and describe what they see but may not diagnose or prescribe.
Worked example
A client has an itchy, scaly patch with broken hairs and asks for a haircut and scalp treatment. Reasoning: broken hairs with scaling suggest a possible fungal infection, which is contagious. The barber should not diagnose, but should decline the service, refer the client to a physician, and disinfect tools and contact surfaces. Cutting first would risk spreading infection.
Traps
- Calling all redness dandruff and proceeding.
- Treating lice or ringworm with a shop product.
- Confusing normal shedding with hair loss disease.
- Forgetting that the cuticle is the layer chemical services alter first.