Scientific Concepts
This domain tests the basic science that explains why services work: the anatomy and physiology of hair, skin, and nails; applied chemistry; and safe electricity. Expect questions that connect a structure to a service outcome, not isolated definitions.
Structures to know
- Hair has three main layers: cuticle (protective outer scales), cortex (bulk; pigment and bonds), and medulla (central core, sometimes absent). The follicle is living; the visible shaft is keratinized and not living.
- Growth cycles: anagen (growth), catagen (transition), telogen (rest). Hair-loss patterns matter when choosing treatments.
- Skin: epidermis (barrier), dermis (nerves, vessels, glands), subcutaneous (fat). The acid mantle is slightly acidic.
- Nail: plate, bed, matrix (growth area), lunula, eponychium, hyponychium.
Chemistry and electricity
pH runs from 0 to 14; below 7 is acidic, 7 is neutral, above 7 is alkaline. Each whole pH unit is a tenfold change in hydrogen ion concentration. Hair and skin prefer about pH 4.5 to 5.5. Chemical services use reduction (perms) and oxidation (color, neutralizer). Electricity requires intact cords, dry hands, and GFCI protection; water and electricity are a dangerous pair.
Worked example
A client's hair is pH 5 and a shampoo is pH 9. How much more alkaline is the shampoo? Four pH units equals 10^4, or 10,000 times. Reasoning: the scale is logarithmic, not linear; the alkaline shampoo swells the cuticle, so follow with an acidic conditioner to help close it.
Traps
Confusing cortex with medulla; calling pH 7 acidic; treating hair as living tissue; assuming all natural products are pH-safe; using electrical tools near water.