Scientific Concepts and Hair Care
What this domain tests
This section tests hair and scalp structure, growth cycles, hair-loss patterns, shampoo and conditioner chemistry, and safe scalp-care decisions. Expect questions that connect anatomy to product choice and that ask when to refer rather than treat.
Core hair facts
- Cuticle is the outer scale layer; it protects the cortex and responds to pH. Cortex is the bulk of the hair and contains melanin and bonds. Medulla is a central core that may be absent, especially in fine or light hair.
- Disulfide bonds give strength and are broken by relaxers and perms. Hydrogen bonds are broken by water and heat and reform on drying. Salt bonds respond to pH changes.
- Hair is acidic, roughly pH 4.5–5.5; alkaline products swell the cuticle and can increase porosity and color fading.
- Growth cycles: anagen (active, years), catagen (transition), telogen (rest/shed). Average scalp growth is about 0.5 inch per month.
- Hair loss patterns include androgenetic, alopecia areata, traction, and telogen effluvium. Cosmetologists do not diagnose; refer.
- Tinea and pediculosis are contagious scalp conditions. Do not serve a client with suspected lice or ringworm; refer and disinfect tools.
Product logic
Shampoos range from clarifying to moisturizing and sulfate-free. Conditioners use cationic surfactants, fatty alcohols, and silicones to smooth the cuticle; apply midshaft to ends and rinse thoroughly. Medicated shampoos are not a cosmetology prescription.
Worked example
A client with color-treated, dry, fine hair asks for a “deep clean.” Reasoning: a high-detergent clarifying shampoo can strip color and moisture. Choose a low-pH moisturizing shampoo, condition the ends, use cooler water, and avoid rough towel drying. If the scalp is red and flaking, do not treat it as ordinary dandruff-refer.
Traps that cost marks
Confusing cuticle with cortex; saying the medulla is always present; treating “pH balanced” as meaning neutral; recommending medicated shampoo for an undiagnosed scalp disease; serving a client with suspected lice.