Anatomy, Physiology and Cosmetic Science
Anatomy, Physiology and Cosmetic Science tests the structures and processes relevant to hair, skin and nails, plus formulation basics: pH, emulsions, surfactants, preservatives and active ingredients.
Core rules
- Skin: epidermis (stratum corneum, keratinocytes), dermis (collagen, elastin, blood vessels, nerves) and hypodermis. The barrier sits mainly in the stratum corneum.
- Hair: cuticle, cortex, medulla; disulphide bonds give strength and shape. Alkaline products swell the cuticle; acidic products help it lie flatter.
- Nails: plate, matrix, bed and surrounding folds; the matrix produces keratin.
- Cosmetic science: surfactants clean by lowering surface tension; emulsions mix oil and water with an emulsifier; preservatives prevent microbial growth. pH matters for compatibility and skin comfort.
Worked example
A conditioner contains a cationic surfactant and citric acid at pH 4. Reasoning: after alkaline shampoo, the cuticle is slightly raised. The acidic formula helps the cuticle compact; the cationic surfactant adsorbs to the negatively charged hair surface, reducing friction and improving combability. It is not repairing broken bonds.
Traps
Calling the stratum corneum living tissue, confusing the dermis with the hypodermis, saying conditioner permanently repairs hair, and ignoring that preservatives are necessary in water-containing products. Also do not claim cosmetics alter skin physiology beyond temporary hydration.