Scientific Concepts
Scientific Concepts
This domain tests the anatomy, physiology, chemistry, and microbiology that underlie every service. Expect questions that connect structure to behavior: why alkaline products swell hair, where melanin sits, how the nail plate grows, and which microbes survive disinfectants.
Hair
A hair follicle has a bulb, root, and shaft. The shaft has three layers: cuticle (overlapping scales), cortex (keratin bundles and melanin), and medulla (a central core that may be absent, especially in fine hair). Growth cycles are anagen (active growth), catagen (transition), and telogen (resting and shedding). Hair is strongest in its natural state; wet hair stretches and breaks more easily. The sebaceous gland attaches to the follicle.
Skin and nails
Skin has epidermis (avascular), dermis (nerves, vessels, glands), and subcutaneous tissue. The nail plate sits on the nail bed, is produced by the matrix, and is sealed by the cuticle. The lunula is visible matrix. The nail plate is dead keratin; the matrix is living tissue.
Chemistry and microbiology
pH measures hydrogen ion concentration: below 7 acidic, 7 neutral, above 7 alkaline. Hair and skin are mildly acidic, about 4.5 to 5.5. Alkaline products raise the cuticle, which helps coloring but increases porosity and dryness. Bacteria are single-celled; viruses need a host; fungi cause ringworm; spores are the toughest. Disinfection destroys most pathogens on surfaces but not spores; sterilization destroys all.
Worked example
A colorist uses a high-pH color on porous, previously lightened hair. The cuticle lifts more than expected, color takes fast, and the ends turn darker. Reasoning: porous hair absorbs more, so processing time and formula strength must be adjusted.
Traps
Do not say the medulla is always present; do not call the nail plate living; do not confuse disinfection with sterilization. Do not assume all scalp hair is in anagen.