Anatomy, Physiology, and Chemistry
Anatomy, physiology, and chemistry questions connect body systems to salon services and explain why products behave as they do. Expect bones and muscles of the face and neck, nerves, circulation, pH, solutions, and chemical bonds.
Core rules
- The skeletal system supports and protects; the muscular system produces movement; the nervous system carries impulses. The fifth cranial nerve (trigeminal) supplies sensation to the face; the seventh (facial) controls facial expression.
- The integumentary system includes skin, hair, and nails. Circulation delivers oxygen and nutrients and removes waste.
- pH is logarithmic: each whole number is a tenfold change. Solutions, suspensions, and emulsions differ in how particles are dispersed. Water is the common solvent in salon chemistry; surfactants have a water-loving head and an oil-loving tail.
- Oxidation loses electrons; reduction gains them. Hair lighteners oxidize pigment; permanent-wave neutralizers rebuild disulfide bonds.
Worked example
A product has pH 4 and another has pH 10. The difference is six pH units, so the second is 10^6, or one million times, less acidic and more alkaline than the first. That reasoning explains why a high-pH product can swell the cuticle and why an acidic conditioner helps restore it.
Traps
Reading pH as a linear scale; mixing up oxidation and reduction; confusing the fifth and seventh cranial nerves; and assuming natural products cannot cause reactions.