Hair Care and Styling: Structure, Services, and Chemical Safety
This domain tests hair structure, growth, scalp health, and the safe execution of cutting, styling, and chemical services. Questions often combine anatomy with a client scenario: what service is contraindicated, what test is required, or which product pH is appropriate.
Hair structure and growth
- The hair fiber has three layers: cuticle (protective scales), cortex (strength, pigment, bonds), and medulla (central core, often absent in fine hair).
- Bonds: disulfide (strongest, changed by relaxers and perms), hydrogen (changed by water and heat), salt, and peptide. Wet hair stretches more and breaks more easily.
- Growth cycles: anagen (active), catagen (transition), telogen (resting and shedding). Average scalp hair grows about ½ inch per month.
Service rules
- Shampoo with a surfactant suited to scalp condition; hot water and high-pH shampoos roughen the cuticle.
- Chemical services require a patch test for color and a strand test for relaxers, perms, and lighteners. Never relax or perm hair with scalp abrasions, recent henna or metallic salts, or contradictory history.
- Thermal tools: use heat protectant, keep irons moving, and respect the manufacturer's temperature range.
Worked example
A client with box-color history and visible breakage requests a double-process blonde. Do a patch test and strand test; if the strand test shows breakage or an unpredictable color result, do not proceed. Reasoning: unknown metallic dyes and overlapping lightener can cause a chemical burn or melt the hair; the strand test predicts the outcome on that client's hair.
Traps
- Believing the cuticle is living tissue.
- Doing a relaxer and perm on the same day.
- Skipping a strand test because the formula always works.
- Using high heat on wet hair without protectant.