Scientific Concepts and Hair Care
This domain tests how well you connect basic anatomy, chemistry, and hair analysis to safe service decisions. Expect questions on hair structure, growth cycles, pH, product ingredients, and the analysis steps that determine whether a chemical service is appropriate.
Hair structure
- Cuticle: outer protective layer of overlapping scales; damage here increases porosity and reduces shine.
- Cortex: main body; contains melanin and disulfide bonds that give strength and shape.
- Medulla: central core; may be absent, especially in fine hair.
Growth and chemistry
- Anagen is the growth phase (roughly 2–7 years), catagen is transition (weeks), and telogen is rest/shed (about 3 months). Most scalp hair is in anagen.
- The pH scale runs 0–14; hair and scalp sit near pH 4.5–5.5. Alkaline products swell and open the cuticle; acidic products tighten it.
- Shampoo surfactants remove oil; conditioners use fatty alcohols and cationic ingredients to smooth the cuticle and reduce static.
Hair analysis
- Porosity: low porosity resists moisture; high porosity absorbs quickly but loses it and is fragile.
- Elasticity: wet hair should stretch and return. If it stays stretched or breaks, avoid aggressive chemicals.
- Density is strands per square inch; texture is strand diameter; growth pattern includes whorls and cowlicks.
Worked example
A client requests a double-process blonde service. You test elasticity: a wet strand stretches and does not recoil. You note high porosity and recent box color. Reasoning: compromised bonds plus overlapping color raise breakage risk. The safe choice is to refuse the full lift, recommend a strand test and a milder deposit or gloss, and book a conditioning plan.
Traps that cost marks
- Confusing density with texture.
- Saying the medulla is always present.
- Reversing pH: alkaline opens the cuticle.
- Treating high porosity as strong hair.