Anatomy and physiology of hair, skin and nails
Anatomy and physiology of hair, skin and nails
This domain tests structure and function at a level needed to explain service effects: why hair feels porous after lightening, why the nail matrix matters, why skin barrier damage limits treatments. Expect labelled structures, growth cycles and the relationship between blood supply, glands and service suitability.
Core rules
- Hair shaft: cuticle (protective scales), cortex (keratin bundles, pigment, strength), medulla (often absent in fine hair).
- Follicle: bulb, matrix, dermal papilla; growth cycle anagen (growth), catagen (transition), telogen (rest), then shedding.
- Skin: epidermis (barrier), dermis (collagen, elastin, vessels, nerves, glands), subcutaneous layer (fat, insulation).
- Nails: plate, matrix, lunula, cuticle, nail folds, hyponychium; growth from the matrix, not the tip.
- Sebaceous glands produce sebum; eccrine sweat glands cool the body; apocrine glands are scent-related.
- Service relevance: chemical damage to the cortex increases porosity; cuticle loss increases friction and breakage; nail plate is non-living keratin.
Worked example
A client's hair snaps when wet after repeated bleach. The stylist explains that the cuticle has lifted and the cortex has lost keratin mass, so elasticity is reduced. They recommend a protein-rich treatment and no further lightening until a strand test shows acceptable elasticity. Reasoning: wet hair stretches; healthy hair returns, over-processed hair stays stretched or snaps.
Traps
Saying the medulla is always present; calling the nail plate living tissue; confusing catagen with telogen; blaming 'dry hair' when the issue is cortex damage; ignoring that scalp blood supply supports follicle activity.