Hair and Scalp Anatomy and Physiology
What this domain tests
Hair and scalp anatomy questions check whether you can connect structure to service outcomes: why the cuticle affects color uptake, why the follicle controls growth, and why scalp health limits chemical services.
Core rules
- The hair shaft has three layers: cuticle (protective outer scales), cortex (bulk, strength, pigment), and medulla (central core, absent in fine or vellus hair).
- The follicle is a tube in the dermis; the bulb at its base contains the matrix and papilla, which supply blood and nutrients. Sebaceous glands attach to the follicle and secrete sebum.
- Growth cycles: anagen (active growth), catagen (transition), telogen (rest). Shedding after telogen is normal; pulling in anagen can damage the follicle.
- Vellus hair is short, fine, and nonpigmented; terminal hair is longer, coarser, and pigmented. Hormones can change one to the other.
- Scalp skin has epidermis, dermis, and subcutaneous layers; inflammation or breaks are contraindications for chemical services.
Worked example
A client's color fades quickly and feels rough. Reason from structure: the cuticle scales are raised or damaged, so pigment leaves faster and light reflects less evenly. Treat gently, avoid overprocessing, and recommend conditioning rather than simply adding more color.
Traps
Saying hair is nourished at the tip, that the medulla is always present, or that cutting makes hair grow faster are common errors. Also distinguish normal shedding from breakage.